Search found 102 matches
- Sat Mar 13, 2021 11:06 am
- Forum: Balancing Redox Reactions
- Topic: Balance reaction using OH- or H+
- Replies: 18
- Views: 759
Re: Balance reaction using OH- or H+
The problem will always make it pretty clear whether the reaction is in acidic or basic solution. If it's acid, you balance the O's with H2O and the H's with H+. If it's basic, you also balance the O's with H2O but then the process becomes a little different. The way I do it is I add double the amou...
- Sat Mar 13, 2021 10:58 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Does temperature affect A?
- Replies: 9
- Views: 559
Re: Does temperature affect A?
A represents the probability that colliding molecules will actually form a transition state and turn into product. Specifically, it describes how many reactants will be in the correct orientation to form a transition state. When T increases, molecules have more KE and will move more, so A should tec...
- Sat Mar 13, 2021 10:54 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: when to add Pt (s)
- Replies: 23
- Views: 928
Re: when to add Pt (s)
Also, as a reminder, a solid does not always mean that it is conductive. For example, I(s) is not conductive, so you would have to include Pt(s). I was confused about that textbook problem at first, but that makes a lot of sense. Even though I is a solid, it's a nonmetal, and cathodes must be condu...
- Fri Mar 12, 2021 3:48 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate Laws for Slow Step/Overall
- Replies: 14
- Views: 861
Re: Rate Laws for Slow Step/Overall
Intermediates cannot be included in the rate law, so you would have to factor it out. You can do this with the pre-equilibrium approach, which Lavelle went over in class. Usually the 1st step is fast, so it will be at equilibrium by the time you get to the 2nd step, which is the slow step. Because o...
- Fri Mar 12, 2021 3:41 pm
- Forum: General Rate Laws
- Topic: Unique Average Rate
- Replies: 4
- Views: 271
Re: Unique Average Rate
Through the model equation: -(1/a)delta[A]/deltaT = (1/b)delta[B]/deltaT for the reaction aA-->bB and the unique average rate, you can relate the rates of all reactants and products to each other. This allows you to find the rate of consumption of A, and relate it to B, for example. The rates are al...
- Fri Mar 05, 2021 12:41 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Arrhenius eq
- Replies: 6
- Views: 406
Re: Arrhenius eq
If you're given the activation energy with a catalyst, and the activation energy without a catalyst for the same reaction, you could use the Arrhenius equation to find the ratio between the reaction rates. You would do this by rearranging the Arrhenius equation to find the ratio between k(catalyst) ...
- Fri Mar 05, 2021 12:35 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts on Final
- Replies: 7
- Views: 524
Re: Catalysts on Final
We would probably have to know some of the basics of a catalyst, and how to identify if there is one. In an energy graph, you would see the peak of the graph, or activation energy, lower if there is a catalyst. The catalyst increases the rates of both the forward and reverse reactions. But catalysts...
- Fri Mar 05, 2021 12:25 pm
- Forum: First Order Reactions
- Topic: Finding order through graphs
- Replies: 17
- Views: 992
Re: Finding order through graphs
The equations for these graphs are on the equation sheet, so I would use that to decide the order with a graph. If there is a straight line with ln[A] vs t, then it matches with the 1st order equation: ln[A]= -kt + ln[A]0 where slope = -k. If there's a straight line with 1/[A] vs t, then it matches ...
- Fri Mar 05, 2021 12:18 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: pseudo rate law
- Replies: 13
- Views: 1019
Re: pseudo rate law
In a pseudo rate law, you would make the concentrations of all but 1 of the reactants so large that the concentration doesn't really change for those reactants. So in an equation with two reactants, Rate = k [A] [B]. This is a 2nd order reaction, but if you make [A]>>>[B], you can make a pseudo 1st ...
- Fri Mar 05, 2021 12:12 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetic control
- Replies: 14
- Views: 853
Re: Kinetic control
In the diamond/graphite example that Lavelle gave us, he used the standard deltaG of the reaction from diamond --> Graphite to determine its thermodynamic stability. DeltaG for this reaction is negative, so the forward reaction is favored and Diamond is thermodynamically unstable. However, this reac...
- Sat Feb 27, 2021 11:20 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Sapling 7/8 Question 17 [ENDORSED]
- Replies: 4
- Views: 402
Re: Sapling 7/8 Question 17 [ENDORSED]
Just to clarify, if the given values are under standard conditions (1 atm / 1 bar, 1M) you don't have to make unit conversions to calculate Q or K? I suppose this is because the Nernst equation uses Ecell standard values, which are all measured at standard conditions, so the given values and the Ece...
- Sat Feb 27, 2021 11:09 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Concentration Cell [ENDORSED]
- Replies: 6
- Views: 367
Re: Concentration Cell [ENDORSED]
Anode: Ag (s) --> Ag+(aq) (0.1 M) + 1e Cathode: Ag+ (0.1 M) + 1e --> Ag (s) Lavelle has these two reactions to describe the concentration cell example from lecture. Can someone walk me through how we develop these with the information given? Thanks! In a concentration cell, oxidation will occur on ...
- Sat Feb 27, 2021 10:59 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: When to use Different Nernst Equations
- Replies: 11
- Views: 833
Re: When to use Different Nernst Equations
If you're at 25 degrees C, you would be fine using: E = E* - 0.05916 Volts/n(log Q) since this equation assumes standard conditions. If you're not at 25 C, you would have to use the basic equation: Ecell=Ecell naught-((R*T)/(n*F))*lnQ. If you want to be 100% sure you're not messing this question up,...
- Sat Feb 27, 2021 10:50 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: dilutions and Ecell
- Replies: 16
- Views: 3153
Re: dilutions and Ecell
i always get a bit confused with this but can someone briefly explain what exactly dilution is please? i guess more specifically, what it means to dilute something/what is happening when something is being diluted Usually when you dilute a solution, you add water to it, which decreases the concentr...
- Sat Feb 27, 2021 10:33 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Gibbs Free Energy Equation and n
- Replies: 13
- Views: 575
Re: Gibbs Free Energy Equation and n
The n you use is the number of moles of e- transferred in the redox reaction after you balance everything. You could also use the number of moles of e- in either of the balanced half reactions.
- Sat Feb 20, 2021 1:57 pm
- Forum: Balancing Redox Reactions
- Topic: Pt in Cell Diagram
- Replies: 14
- Views: 873
Re: Pt in Cell Diagram
You would use Pt if the species of the redox reaction aren't in solid form. This is because you need a solid metal to act as an electrode in a redox reaction, and Pt is commonly used for this job since it isn't reactive.
- Sat Feb 20, 2021 1:55 pm
- Forum: Balancing Redox Reactions
- Topic: Cathode and Anode
- Replies: 24
- Views: 1537
Re: Cathode and Anode
When E(cell) is not = 0, the cell can do work. Since E(cell) = E(cathode) - E(anode), if E(cell) is > 0, that means E(cathode) > E(anode) and the cell will do work. I assume that E(cell) can also be < 0 and do work, and in this case E(anode) > E(cathode)?
- Sat Feb 20, 2021 1:51 pm
- Forum: Balancing Redox Reactions
- Topic: Change in potential as i -> 0
- Replies: 12
- Views: 571
Re: Change in potential as i -> 0
i represents the current of e-, so when i --> 0, very little current flows. This will give you the electromotive force (emf) of the cell, which is the cell's maximum potential difference between electrodes.
- Sat Feb 20, 2021 1:46 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 9
- Views: 619
Re: Oxidation Numbers
To figure out the oxidation numbers in a compound, you would probably have to memorize the oxidation number rules, then figure out the remaining elements in the compound based on that. So pure elements are 0, group 1 metals are +1, group 2 metals are +2, H is +1, group 7 is -1 with some exceptions, ...
- Sat Feb 20, 2021 1:40 pm
- Forum: Balancing Redox Reactions
- Topic: Salt Bridges
- Replies: 21
- Views: 775
Re: Salt Bridges
Without the salt bridge, there would be too many e- on the cathode side, giving the cathode beaker a net negative charge which prevents further e- transfer. The salt bridge allows anions (like Cl-) to transfer to the anode side. As the cathode side gets more e- and becomes more negative, the anions ...
- Sat Feb 13, 2021 12:44 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Standard Gibbs Free Energy
- Replies: 8
- Views: 465
Re: Standard Gibbs Free Energy
Standard Gibbs free energy is related to K by the equation deltaG standard = -R * T * lnK. This equation is helpful since, if you know deltaG standard, you could figure out what K is which would give you an idea of the concentrations of the species in the reaction at equilibrium. DeltaG would also t...
- Sat Feb 13, 2021 12:30 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: deltaS equations
- Replies: 8
- Views: 318
Re: deltaS equations
You would use deltaS = q/T when temperature is constant. We would probably use this for phase changes, so use deltaH of vaporization and boiling point to find deltaS of vaporization. Use deltaS = nR*ln(V2/V1) when there is a change in volume for an isothermal reversible expansion, and deltaS total =...
- Sat Feb 13, 2021 12:22 pm
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Determining Different States
- Replies: 4
- Views: 242
Re: Determining Different States
In that example, the atoms A and B could be in two different states, either on the left or right of the flask. In order to calculate W, you would do 2^2 = 4. This correlates to the number of microstates in the system, or the different ways that the atoms can be arranged. You could have A and B on th...
- Sat Feb 13, 2021 12:16 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Larger molar entropy leads to a higher ordered arrangement?
- Replies: 3
- Views: 169
Re: Larger molar entropy leads to a higher ordered arrangement?
I think another way to think about it is that deltaS is directly related to q with deltaS=q/T. You would need a greater q to vaporize a highly ordered molecule, so there would be a greater deltaS value. So the higher the deltaS, the more energy you need to make a phase change, and the more ordered t...
- Sat Feb 13, 2021 11:54 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isothermal Reactions
- Replies: 26
- Views: 1171
Re: Isothermal Reactions
Yes, isothermal expansions are always reversible. This is because a reversible expansion happens so slowly that external heat has enough time to enter the system and restore the internal energy that's being used up as work in the expansion.
- Thu Feb 04, 2021 2:12 pm
- Forum: Calculating Work of Expansion
- Topic: Work on surrounding
- Replies: 12
- Views: 410
Re: Work on surrounding
Dr. Lavelle mentioned that aq, l, and s species in the reaction don't contribute to any change in PdeltaV. This is because the volume of these states of matter doesn't change much in reactions. So you would not consider the solid in this reaction when you're determining work.
- Thu Feb 04, 2021 2:06 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: W
- Replies: 14
- Views: 510
Re: W
Yup, N refers to the number of molecules in the system. Since carbon monoxide is just CO, there are 2 atom positions per molecule, or there are only 2 possible states per molecule. To find the overall W, you would do 2^4 since this system has 4 CO molecules.
- Thu Feb 04, 2021 11:15 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Sapling Week 3 and 4 Question 18
- Replies: 5
- Views: 158
Re: Sapling Week 3 and 4 Question 18
Here is what I had for my question: A 0.773 mol sample of CO2(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 15.7 K. Calculate the amount of heat q required to bring about this temperature change, and find the cor...
- Thu Feb 04, 2021 10:44 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Sapling Weeks 3 and 4 HW Question 12
- Replies: 3
- Views: 93
Re: Sapling Weeks 3 and 4 HW Question 12
For a calorimeter problem like this, I suppose you could say that the heat given off by the rxn (since it's exothermic) = -heat absorbed by the calorimeter. So the calorimeter absorbs the heat given off by the combustion rxn, and you can use this relationship to set up q=c*deltaT to find the c of th...
- Thu Feb 04, 2021 10:35 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calorimeters
- Replies: 15
- Views: 537
Re: Calorimeters
So we would probably have to know the general design and reason to use each type of calorimeter? The styrofoam cup calorimeter is used for constant P calorimetry. Since it's just an open cup with a thermometer in it, it's open to the pressure of its surroundings, which is constant. The bomb calorime...
- Thu Jan 28, 2021 4:31 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating the pH of Industrial, Environmental, and Biological Examples [ENDORSED]
- Replies: 3
- Views: 252
Re: Calculating the pH of Industrial, Environmental, and Biological Examples [ENDORSED]
If you wanted to find the pH of carbonic acid, I'm pretty sure you would only need to take the 1st deprotonation into account since the second deprotonation would make an insignificant amount of H3O+. I think the only polyprotic acid that we need to take the 2nd deprotonation into account is sulfuri...
- Thu Jan 28, 2021 4:23 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Combustion of nitrogen for enthalpy of combustion reactions
- Replies: 2
- Views: 2321
Re: Combustion of nitrogen for enthalpy of combustion reactions
The combustion of N2 would make NO, so the reaction would be N2 + O2 --> 2NO. If you wanted to make NO2, you would have to do 2NO + O2 --> 2NO2. And when Nitrogen is in a molecule that's being combusted, it turns into N2 gas.
- Thu Jan 28, 2021 4:17 pm
- Forum: Phase Changes & Related Calculations
- Topic: H and q
- Replies: 47
- Views: 1534
Re: H and q
q represents the amount of heat released or absorbed in a system in J. Delta H represents the amount of heat released or absorbed AT CONSTANT PRESSURE. So you can think of it like q sub p = deltaH.
- Thu Jan 28, 2021 4:09 pm
- Forum: Phase Changes & Related Calculations
- Topic: standard form
- Replies: 14
- Views: 695
Re: standard form
So it would be helpful to memorize the standard forms of N2, O2, H2, F2, and Cl2 being gases. Br2 is a liquid, I2 is a solid, C is solid graphite, and Hg is a liquid. The enthalpies of formation for the standard state is 0 because the molecules are already at their most stable form, so they won't be...
- Thu Jan 28, 2021 4:06 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Question About State Properties and Hess's Law
- Replies: 4
- Views: 128
Re: Question About State Properties and Hess's Law
State properties are additive, so if you add up all of the enthalpies for each individual step, you will get the correct enthalpy change for the overall reaction. You can't take the enthalpy of one step and the enthalpy of the last step and use that to find deltaH because the steps don't really refl...
- Thu Jan 21, 2021 3:59 pm
- Forum: Phase Changes & Related Calculations
- Topic: bonds and energy
- Replies: 13
- Views: 638
Re: bonds and energy
Breaking bonds requires energy since you have to overcome the potential energy that holds the atoms together, making it endothermic. Making bonds releases energy since the kinetic energy of the atoms that were previously moving around is released once they are bonded together.
- Thu Jan 21, 2021 3:52 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes of Water Graph
- Replies: 7
- Views: 334
Re: Phase Changes of Water Graph
The slope from solid to the freezing point is steeper than the slope from the freezing to boiling point because it takes more energy to change water from a liquid to gas than from a solid to liquid.
- Thu Jan 21, 2021 3:44 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Endothermic vs Exothermic Stabilities
- Replies: 8
- Views: 3608
Re: Endothermic vs Exothermic Stabilities
You're right because lower energy is favored in reactions. So in an endothermic reaction, the products are less stable than the reactants because the products have more energy than the reactants. So the reaction would naturally want to go in the reverse direction, towards less energy. On the other h...
- Thu Jan 21, 2021 3:37 pm
- Forum: Phase Changes & Related Calculations
- Topic: Lecture #7 Question
- Replies: 7
- Views: 161
Re: Lecture #7 Question
Looking at the phase diagram, it takes a lot more energy to go from a liquid at 25 C to a vapor at 100 C than from a liquid at 25 C to a liquid at 100 C. This additional heat from the vaporization phase change will be released when the vapor comes into contact with skin. So the vapor will release a ...
- Thu Jan 21, 2021 3:32 pm
- Forum: Phase Changes & Related Calculations
- Topic: enthalpy vs temperature
- Replies: 8
- Views: 1460
Re: enthalpy vs temperature
Temperature describes the average kinetic energy of the molecules WITHIN the system, or how much energy the molecules in the system contains. Temperature is measured in K or Celsius. Enthalpy is the amount of heat RELEASED or ABSORBED by the system at constant pressure. And heat describes the TRANSF...
- Sat Jan 16, 2021 11:36 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Memorizing relationship of Q and K
- Replies: 9
- Views: 416
Re: Memorizing relationship of Q and K
I agree that I would think about what it means quantitatively if Q < K or vice versa. If Q > K, that means the numerator of Q is greater than the denominator, so there are too many products. In order to offset this difference, the products would react and turn into reactants. This would increase the...
- Sat Jan 16, 2021 11:33 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: K in endo and exo when temp. decreases
- Replies: 11
- Views: 497
Re: K in endo and exo when temp. decreases
I was also a little confused about this on Sapling. From what I understand, if temperature is decreased in an exothermic reaction, more products would be formed since heat is a product. This will increase the value of K, resulting in Q < K. Similarly, if temperature is decreased in an endothermic re...
- Sat Jan 16, 2021 11:28 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Gas
- Replies: 16
- Views: 574
Re: Gas
Although bar is technically the correct unit to use for pressure in equilibrium equations, we use bar and atm interchangeably in this class. Dr. Lavelle said that we will usually use atm, but a problem might give you bar instead.
- Sat Jan 16, 2021 11:26 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Autoprotolysis
- Replies: 5
- Views: 330
Re: Autoprotolysis
Just to reiterate, the autoprotolysis equation was given to us so that we could quantitatively understand the equations for Kw and pKw that we use so often. The relationship of [H3O+] [OH-] = 10^-14 is important to calculate pH, pOH, and concentrations of the H+ and OH- ions. Also, when water is inv...
- Sat Jan 16, 2021 11:16 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Predominant Species
- Replies: 3
- Views: 231
Re: Predominant Species
I suppose the predominant species is the one that will make the pH value closer to the pKa value. For example, if the pH of an acid is higher than the pKa, it will make the deprotonated A- in order to lower the pH. The H+ that the A- species gave away would lower the pH, making it closer to the pKa ...
- Sun Jan 10, 2021 11:30 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Conceptual Understanding of Decrease in Volume
- Replies: 3
- Views: 109
Re: Conceptual Understanding of Decrease in Volume
When volume is decreased, the value of Q for the reaction changes. This is because Q = [P] / [R] and concentration = n/V. Since n doesn't change and V does, the concentrations of the gases change when volume is decreased. So Q would be different from K, resulting in a shift depending on whether it's...
- Sun Jan 10, 2021 11:25 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Definition of an Inert Gas
- Replies: 15
- Views: 892
Re: Definition of an Inert Gas
An inert gas doesn't react with any other compounds, so when you add it into a container, it won't cause a change in concentration for anything involved in the reaction. I suppose that in real life adding an inert gas in a closed container would slightly decrease the volume, since the particles take...
- Sun Jan 10, 2021 11:22 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Water
- Replies: 28
- Views: 917
Re: Water
Water is only included when it is a gas that's involved in the reaction. When it's a pure solid or liquid, its concentration doesn't change, so you wouldn't have to include it in the equilibrium constant equation. When water acts as a solvent, there is so much of it compared to the species involved ...
- Sun Jan 10, 2021 11:19 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Fall 2010, Question #6C (Equilibrium shifts right or left?)
- Replies: 4
- Views: 494
Re: Fall 2010, Question #6C (Equilibrium shifts right or left?)
I suppose that these types of questions ask more about the long term behavior of the equilibrium. So, initially, there are more products when NO2 is added. Over time, this additional product is used up to produce more reactants in order to return to the equilibrium constant value. So the equilibrium...
- Sun Jan 10, 2021 11:15 am
- Forum: Ideal Gases
- Topic: Ideal Gas Assumptions
- Replies: 4
- Views: 233
Re: Ideal Gas Assumptions
So, just to clarify, ideal gases have 3 assumptions. 1) They have completely elastic collisions so the particles don't lose energy in a closed space. 2) The molecules are treated as points in space which don't have volume, so the molecules themselves don't take up any volume. 3) Molecules don't chan...
- Thu Dec 17, 2020 12:11 pm
- Forum: Air Pollution & Acid Rain
- Topic: Acid Rain
- Replies: 24
- Views: 3814
Re: Acid Rain
CO2, SO2, and NO2 are all pollutants that react with water to form slightly acidic solutions. CO2 produces carbonic acid, which has a slightly higher pH than the sulfurous acid and nitric acid that's formed by SO2 and NO2. So these acidic solutions act as acid rain in the real world.
- Sat Dec 12, 2020 1:43 pm
- Forum: Properties & Structures of Inorganic & Organic Bases
- Topic: 6B.5
- Replies: 8
- Views: 1429
Re: 6B.5
Since these are all strong, you can assume they will be completely dissociated. So 0.0146M of HNO3 would make 0.0146M H+. It's important to remember that 0.0092M of Ba(OH)2 would make 2 * 0.0092M of OH- since 1 molecule creates 2 OH-.
- Sat Dec 12, 2020 1:39 pm
- Forum: Amphoteric Compounds
- Topic: How to know if a molecule is amphoteric
- Replies: 9
- Views: 1927
Re: How to know if a molecule is amphoteric
In one of the lectures, Dr. Lavelle showed us that the metalloid oxides are also common amphoteric molecules. Other than that, it's helpful to look at the compound and see if it can donate and accept an H+. The compound is usually negatively charged, so it can donate an H+ and receive it again.
- Sat Dec 12, 2020 1:27 pm
- Forum: Bronsted Acids & Bases
- Topic: Bronsted vs Lewis Acids and Bases
- Replies: 8
- Views: 547
Re: Bronsted vs Lewis Acids and Bases
All Bronsted acids/bases are Lewis acids/bases, but not the other way around. So, in the case of Cl- + SO2 --> SO2Cl, H+ isn't involved at all, so there can't be any Bronsted acids or bases. The Cl- does donate a lone pair to the SO2 to create SO2Cl, so the Cl- is a lewis base and the SO2 is a lewis...
- Sat Dec 12, 2020 1:19 pm
- Forum: Conjugate Acids & Bases
- Topic: Amphoteric
- Replies: 11
- Views: 514
Re: Amphoteric
Amphoteric compounds can act as either acids or bases depending on what they're exposed to. Polyprotic acids are common examples of this, since they can gain or lose an H+ depending on the situation. H2O is also a common example since it can gain H+ to become H3O+, or lose an H+ to become OH-.
- Sat Dec 12, 2020 1:12 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Acidic, basic, or neutral?
- Replies: 10
- Views: 1576
Re: Acidic, basic, or neutral?
The solution is acidic because NH4Cl has a strong acid and weak base. The Cl- is from a strong base, so it won't change the pH. However, the NH4+ isn't from a strong acid or base, so it will react with water. It will donate its H+ to water to form H3O+, making the solution acidic, because NH4+ + H2O...
- Fri Dec 04, 2020 2:43 pm
- Forum: Properties & Structures of Inorganic & Organic Bases
- Topic: Is trichloroacetic acid stronger than acetic acid?
- Replies: 5
- Views: 707
Re: Is trichloroacetic acid stronger than acetic acid?
Yes, because the Cl's in trichloroacetic acid pulls more on the electrons in the anion than the H's in acetic acid. The resonance in trichloroacetic acid also makes it relatively strong.
- Fri Dec 04, 2020 2:40 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: How do you know if something is a salt solution?
- Replies: 6
- Views: 686
Re: How do you know if something is a salt solution?
Since a salt is a compound with a cation and anion that dissociates in water, just treat this problem like a normal problem to find pH. You would use the basic equation of Salt+Water--->Acid+Base to figure out what the acid is, then use that information to find pH with the pH equation.
- Fri Dec 04, 2020 2:34 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: pKa and Ka
- Replies: 10
- Views: 577
Re: pKa and Ka
Ka is the concentration of products ([H+] and [A-]) over reactants ([AH]) and pKa is the negative log of the answer to that. A strong acid dissociates almost completely, so the numerator in that equation would be very high compared to the denominator, giving you a high Ka and a low pKa. This is why ...
- Fri Dec 04, 2020 2:28 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Acid Bond Strength
- Replies: 5
- Views: 266
Re: Acid Bond Strength
Bond strength is probably the easiest thing to consider as long as the bonds being broken involve different species. If not, you have to look at the stability of the anion, which involves whether it has resonance structures or if it has more electron pulling power (IE) than the anion in the other ac...
- Fri Dec 04, 2020 2:20 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Stronger acid?
- Replies: 13
- Views: 1163
Re: Stronger acid?
HClO2 would be the stronger acid because it has more O atoms than HClO. Since the same O-H bond is being broken for both acids, you would have to look at how strong the electron pulling power of each anion is. Since ClO2 has more O, it would pull on the electron density of the compound stronger, res...
- Fri Nov 27, 2020 4:04 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: coordination number
- Replies: 13
- Views: 577
Re: coordination number
The coordination number is the number of bonds. So, if there is a double bond in a coordination compound, that would count as a coordination number of 2.
- Fri Nov 27, 2020 4:03 pm
- Forum: Naming
- Topic: NH4[PtCl3(NH3)]
- Replies: 6
- Views: 832
Re: NH4[PtCl3(NH3)]
Since the ammonium is bonded to the coordination complex, the compound must be an anion. If the coordination compound is an anion, then the TM has an -ate name.
- Fri Nov 27, 2020 3:58 pm
- Forum: Naming
- Topic: chelating ligand
- Replies: 7
- Views: 432
Re: chelating ligand
Chelates need to have single bonds and lone pairs in their structures to be able to surround a TM in a ring shape. You can see that the four acetates in this structure are bonded to the N atoms with single bonds, and the N atoms have lone pairs. This single C-N bond will allow the molecule to rotate...
- Fri Nov 27, 2020 3:51 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Coordination number
- Replies: 9
- Views: 356
Re: Coordination number
The coordination number is the actual number of bonds, so you would count a double bond as having a coordination number of 2. The number of ligands would only tell you what is being bonded to the TM, so the number of bonds is what really determines coordination number.
- Fri Nov 27, 2020 3:48 pm
- Forum: Hybridization
- Topic: e density
- Replies: 30
- Views: 1030
Re: e density
Regions of electron density count as both the bonding and non-bonding parts of a compound. The bonding parts, which are covalent bonds, are counted as one region of e- density regardless of being single, double, or triple bonded. The non-bonding parts, which are the lone e- pairs, are also considere...
- Fri Nov 27, 2020 3:45 pm
- Forum: Hybridization
- Topic: Question about Hybridized Orbitals
- Replies: 5
- Views: 254
Re: Question about Hybridized Orbitals
The energy difference between an sp orbital and p orbital is less than the energy difference between an s and p orbital. This is because an sp orbital's energy is the average of the s and p orbitals, so its higher energy than s, but lower than p. The lower energy difference is another reason why C i...
- Sat Nov 21, 2020 12:17 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizability vs Polarizing Power in anions/cations & bonding
- Replies: 10
- Views: 508
Re: Polarizability vs Polarizing Power in anions/cations & bonding
Polarizability is how easy it is to distort the electrons in an ion. A large anion like Te2- would be highly polarizable because it has many shells of electrons, making the outer electrons easy to distort due to shielding. A small, highly charged cation like B3+ is very polarizing because its high c...
- Sat Nov 21, 2020 12:13 pm
- Forum: Coordinate Covalent Bonds
- Topic: General Question on Coordinate Covalent Bonds
- Replies: 8
- Views: 590
Re: General Question on Coordinate Covalent Bonds
A coordinate covalent bond happens when a lewis acid donates both electrons from a lone pair to a lewis base, which needs two electrons to fill its octet. So, in the case of BF3 and NH3, you know there is a coordinate covalent bond because the B only has 6 electrons, so it needs the lone pair from N...
- Sat Nov 21, 2020 12:08 pm
- Forum: Octet Exceptions
- Topic: Octet Rule Exceptions
- Replies: 20
- Views: 1296
Re: Octet Rule Exceptions
The first four elements, H, He, Li, and Be only need two electrons to fill their orbital since they bond to try to fill the 1s orbital. The elements in group 13 only need 6 electrons, and elements in period 3 and lower on the periodic table can have more than eight electrons in their outer shell due...
- Sat Nov 21, 2020 12:04 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: What exactly is a dipole? [ENDORSED]
- Replies: 16
- Views: 1132
Re: What exactly is a dipole? [ENDORSED]
Dipoles are the result of uneven electron sharing in a covalently bonded compound. In water, for example, the O is more electronegative than the H's, so the O pulls more electrons towards it and creates a negative dipole moment. When two nonpolar molecules come close to each other, the electrons of ...
- Sat Nov 21, 2020 12:00 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: High Vapor Pressure, Solubility, Boiling Point
- Replies: 5
- Views: 335
Re: High Vapor Pressure, Solubility, Boiling Point
If a compound has a high vapor pressure, it also has low solubility and low boiling point. This is because vapor pressure measures how much gas is created from a liquid, and if a compound has low IMF, then it would release a large amount of gas and create high vapor pressure. This low IMF would also...
- Sat Nov 14, 2020 10:00 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: n, l, mi
- Replies: 8
- Views: 519
Re: n, l, mi
n corresponds to the energy level or shell. l is angular momentum and it describes the shape of the orbital, whether it's s, p, d, or f. m is the spin of the electron and indicates the orbital's orientation.
- Sat Nov 14, 2020 9:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: H3O+
- Replies: 12
- Views: 26107
Re: H3O+
H3O+ is tetrahedral because it has 8 total valence electrons, so there must be a bond between each of the 3 H atoms and the O, leaving a lone pair on the O.
- Sat Nov 14, 2020 9:42 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: H-F H-F Hydrogen Bonding vs Dipole-Dipole
- Replies: 11
- Views: 1390
Re: H-F H-F Hydrogen Bonding vs Dipole-Dipole
The bond between the H and the F would be both a dipole-dipole bond and a hydrogen bond, since hydrogen bonds are basically stronger versions of regular dipole-dipole bonds. So, I would think that this attraction should be -20kj/mol, rather than -2kj/mol.
- Sat Nov 14, 2020 9:38 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Textbook #3F1
- Replies: 4
- Views: 266
Re: Textbook #3F1
Although the electronegativity difference between S and O in SO2 isn't very large, the bent shape of the molecule itself causes a negative dipole moment around the two O atoms, and a positive dipole moment around the S atom.
- Sat Nov 14, 2020 9:35 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Hydrogen bonding why it works?
- Replies: 4
- Views: 257
Re: Hydrogen bonding why it works?
Although it's called hydrogen "bonding," it isn't an actual bond. Hydrogen bonding is an intermolecular force between the H in one molecule and an N, O, or F in another molecule. Actual bonds are intramolecular forces like ionic and covalent bonds between atoms in a molecule.
- Thu Nov 05, 2020 5:22 pm
- Forum: Resonance Structures
- Topic: Limitations of Lewis Structures
- Replies: 6
- Views: 894
Re: Limitations of Lewis Structures
Lewis structures are limited in that it appears they portray elements in compounds as containing single or double bonds, or there are two electrons assigned to a specific element, and there are different ways to draw resonant structures. In reality, the bonds between atoms meld together to become an...
- Thu Nov 05, 2020 5:17 pm
- Forum: Resonance Structures
- Topic: Expanded Octet Examples
- Replies: 5
- Views: 1464
Re: Expanded Octet Examples
Going off of what Vivian was saying, we only need to know the octet exception for P, S, and Cl. Although S normally has an electron config of [Ne] 3s^23p^4, is has n=3, so there is still room in the empty d orbital to put electrons if the 3p electrons move to the 3d subshell.
- Thu Nov 05, 2020 5:13 pm
- Forum: Lewis Structures
- Topic: favored structure
- Replies: 5
- Views: 125
Re: favored structure
It is B because the favored structure is the one that has atoms closest to a formal charge of 0. You can't get to a formal charge of 0 in this case, so you would want to choose the structure with the most electronegative element as a negative formal charge, which b has since O is negative.
- Thu Nov 05, 2020 5:06 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma vs. Pi
- Replies: 20
- Views: 1176
Re: Sigma vs. Pi
Sigma bonds are stronger because they occur for single bonds or the first bond between atoms, allowing the orbitals to overlap on their ends and giving enough flexibility for the bond to rotate when the molecule rotates. Pi bonds occur on the second or third bond, so their orbitals overlap side to s...
- Thu Nov 05, 2020 5:01 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic Bonding Question
- Replies: 6
- Views: 584
Re: Ionic Bonding Question
The elements on the right are nonmetals, which are very electronegative due to their closeness to the noble gases. This causes them to gain electrons, becoming anions (negative). The elements on the left are metals, which are less electronegative since they can get closer to noble gas valence electr...
- Thu Oct 29, 2020 4:52 pm
- Forum: *Shrodinger Equation
- Topic: Wave Function
- Replies: 5
- Views: 332
Re: Wave Function
So, looking at the slides from the lecture, the wave function represents the height of the electron's wave at x,y,z. Each way of solving the wave function gives you a different orbital, so solving the wave function one way will give you the s orbital, and solving another way will give you the p orbi...
- Thu Oct 29, 2020 4:46 pm
- Forum: *Shrodinger Equation
- Topic: The Hamiltonian
- Replies: 8
- Views: 382
Re: The Hamiltonian
In the equation H*wave function=E*wave function, the wave function stays the same on both sides of the equal sign, so H and E must be equal to each other. E represents the energy of the electron in an atom, so if you take the double derivative of the wave function, you get the energy of the electron.
- Thu Oct 29, 2020 4:35 pm
- Forum: DeBroglie Equation
- Topic: When to Use De Broglie
- Replies: 16
- Views: 1413
Re: When to Use De Broglie
You only use E=hc/lambda for finding the energy of photons, since this equation doesn't have mass. Something helpful for me to remember is that whenever there is just an E in our equation sheet (not Ek or En), the equation is for photons. To find the energy of an electron or something else with mass...
- Thu Oct 29, 2020 4:32 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: En and E
- Replies: 3
- Views: 121
Re: En and E
En is the energy at an energy level n. This is different from E, which on our equation sheet, represents the energy of a photon. So, E=hv and E=pc on our equation sheet both give the energy of a photon.
- Thu Oct 29, 2020 4:25 pm
- Forum: Properties of Light
- Topic: Do we need to know the ranges of waves on the electromagnetic spectrum?
- Replies: 7
- Views: 234
Re: Do we need to know the ranges of waves on the electromagnetic spectrum?
So, I suppose it would be good to memorize the electromagnetic spectrum for this test? According to the book, the wavelength of radio waves are greater than 10cm, microwaves are between 10cm and 1mm, infrared is between 1mm and 1 micrometer, visible is between 700nm and 420nm with 700 being red and ...
- Sun Oct 25, 2020 11:52 am
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Midterm 1
- Replies: 18
- Views: 575
Re: Midterm 1
Some of the conceptual points we would probably have to know about the Heisenberg equation is that delta x and delta p represent the indeterminacy in momentum and position for an electron, and there is a limit to how certain you can be of either.
- Sun Oct 25, 2020 11:45 am
- Forum: DeBroglie Equation
- Topic: De Broglie Equation v. Speed of Light Equation
- Replies: 14
- Views: 547
Re: De Broglie Equation v. Speed of Light Equation
The de Broglie equation gives you the wavelength and momentum of something with mass. Since photons don't have mass, you would have to use the speed of light equations.
- Sun Oct 25, 2020 11:41 am
- Forum: *Particle in a Box
- Topic: Midterm 1
- Replies: 17
- Views: 1270
Re: Midterm 1
In one of the lectures, Dr. Lavelle said that the particle in a box model basically says that the electron in a Hydrogen atom is bond within the radius of the hydrogen atom. So the electron is "trapped" in this box that is the hydrogen atom.
- Sun Oct 25, 2020 11:36 am
- Forum: *Shrodinger Equation
- Topic: Wave function
- Replies: 8
- Views: 420
Re: Wave function
The psi symbol is the wave function, which represents the probability region and momentum of an electron. I understand that the hamiltonian is the left part of Schrodinger's Equation, but I don't understand what people mean when they say it is the second derivative.
- Sun Oct 25, 2020 11:28 am
- Forum: *Shrodinger Equation
- Topic: Schrodinger on MT
- Replies: 7
- Views: 407
Re: Schrodinger on MT
I'm thinking we will probably also have to know what each part of Schrodinger's Equation represents. So, the part with the fractions represents kinetic energy, the part with V represents potential energy, and these together equal total energy of the system
- Sat Oct 17, 2020 12:40 pm
- Forum: *Shrodinger Equation
- Topic: Schrodinger for exam
- Replies: 20
- Views: 795
Re: Schrodinger for exam
I suppose we should know that solving Schrodinger's equation would give you a range of positions and momentums for a wave. But due to the uncertainty principle, the equation won't give you an exact answer for both position and momentum. The orbital of an electron would definitely matter to find its ...
- Sat Oct 17, 2020 12:32 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Jumping energy levels vs. Removing an electron
- Replies: 3
- Views: 132
Re: Jumping energy levels vs. Removing an electron
Ionization energy is how much energy is required to remove an electron from the outer ring of an element, and since every element has a different number of protons and electrons, this energy differs for each element. Maybe you could plug the ionization energy of an element into one of these equation...
- Sat Oct 17, 2020 12:22 pm
- Forum: *Black Body Radiation
- Topic: Understanding Black Body Radiation
- Replies: 8
- Views: 670
Re: Understanding Black Body Radiation
So, just to make sure I understand correctly, a black body absorbs all frequencies of light and emits radiation based on the incoming wavelength of light, so it can emit any wavelength of light. This emission from the black body is the black body radiation.
- Sat Oct 17, 2020 12:15 pm
- Forum: Properties of Electrons
- Topic: Wave Properties of Electrons
- Replies: 5
- Views: 233
Re: Wave Properties of Electrons
So, looking at the DeBroglie equation, wavelength = h/p, and we know p = mv. Since electrons have such a small mass, the p is relatively small, which makes the wavelength for an electron much larger and more noticeable than a relatively massive object like a baseball. The double slit experiment refl...
- Sat Oct 17, 2020 12:09 pm
- Forum: Properties of Light
- Topic: Balmer and Lyman series
- Replies: 7
- Views: 272
Re: Balmer and Lyman series
So, based on everyone's replies, it seems the Lyman series describes electrons that drop to n=1, and the Balmer series describes electrons that drop to n=2. Electrons from the Lyman series emit UV radiation because it takes more energy to drop all the way down to n=1. So electrons from the Balmer se...
- Sat Oct 10, 2020 11:12 am
- Forum: Limiting Reactant Calculations
- Topic: Limiting reactants in all chemical rxns?
- Replies: 18
- Views: 608
Re: Limiting reactants in all chemical rxns?
If you could somehow match the moles of the reactants perfectly to the stoichiometric coefficients in their reaction, then there would be no limiting reactant. However, this is highly improbable because each molecule and element has its own unique molar mass, which would require an infinite number o...
- Sat Oct 10, 2020 11:08 am
- Forum: Empirical & Molecular Formulas
- Topic: Rounding up for Empirical Formulas?
- Replies: 10
- Views: 798
Re: Rounding up for Empirical Formulas?
I think that Reva's approach would be the best when you are having trouble finding a number to multiply your empirical formula by. It will ensure that you are getting the lowest ratio of whole numbers for your formula. However, you would usually be fine just multiplying your formula by different num...
- Sat Oct 10, 2020 11:02 am
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Molecules, and Formula Units
- Replies: 4
- Views: 178
Re: Molecules, and Formula Units
So, based on this textbook question, the number of atoms would apply to a single element, the number of molecules would apply to a covalently-bonded molecule, and formula units would apply to ionic compounds?