Search found 101 matches
- Wed Mar 11, 2020 2:32 pm
- Forum: Balancing Redox Reactions
- Topic: Half Reactions
- Replies: 15
- Views: 804
Re: Half Reactions
Dr. Lavelle has a great instructional sheet on his website on how to balance redox reactions. It explains all of this is detail. Helped me a lot for test 2
- Wed Mar 11, 2020 2:25 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Derivation of Arrhenius Equation
- Replies: 6
- Views: 479
Re: Derivation of Arrhenius Equation
This is done using two different symbolic temperature values, plugging them into the Arrhenius Equation, and subtracting these equations to solve for the rate constants. Pretty much the same as what we did for the Van't Hoff equation (relating temperature changes to a change in K)
- Wed Mar 11, 2020 2:21 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Difference between catalyst and intermediate
- Replies: 9
- Views: 634
Re: Difference between catalyst and intermediate
Catalysts are consumed then regenerated throughout the course of the reaction. Intermediates are produced during one step and consumed in another step of the reaction. Both will cancel out of the final equation.
- Tue Mar 10, 2020 9:08 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts and Rates
- Replies: 10
- Views: 658
Re: Catalysts and Rates
Catalysts DO speed up reactions. You're right that catalysts lower activation energy by providing an alternate mechanism for the reaction. If you look at the exponential form of the Arrhenius equation, when you decrease activation energy, you are increasing the rate of the reaction exponentially.
- Mon Mar 09, 2020 12:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: gibbs free energy
- Replies: 15
- Views: 801
Re: gibbs free energy
Gibbs free energy is the maximum amount of energy released during a reaction that is available to do work (i.e. that energy can be used for other purposes)
- Sun Mar 08, 2020 11:40 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Calculating ln Q
- Replies: 20
- Views: 1545
Re: Calculating ln Q
The ion in aqueous solution that is growing in concentration is the product (i.e. at the anode). The ion in aqueous that is decreasing in solution (i.e. at the cathode) is the reactant. The pure metal at the anode and cathode is not involved in Q because they are solids. Solids and solvents don't fa...
- Sun Mar 08, 2020 11:37 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Concentration Cell
- Replies: 7
- Views: 490
Re: Concentration Cell
A concentration essentially uses the -(RT/nF)lnQ term of the Nernst Equation to generate (a small amount) of electricity. Since the half reactions at the cathode and anode are the same, the standard cell potential is zero. Therefore, the difference in concentration (i.e. Q) makes the overall cell po...
- Sun Mar 08, 2020 11:31 pm
- Forum: Balancing Redox Reactions
- Topic: Cathode and Anode
- Replies: 24
- Views: 1570
Re: Cathode and Anode
Because if there is still potential difference between the cathode and anode, then the reaction is not at equilibrium, and electrons will continue to flow from the cathode to the anode. This generates electricity.
- Sun Mar 08, 2020 11:25 pm
- Forum: Second Order Reactions
- Topic: Termolecular
- Replies: 43
- Views: 2275
Re: Termolecular
Three reactant molecules are involved to form the products in a single step.
- Sun Mar 08, 2020 11:13 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: A in the Arrhenius Equation
- Replies: 8
- Views: 539
Re: A in the Arrhenius Equation
A is the fraction of molecular collisions that occur at the proper angle for a reaction to occur.
- Thu Mar 05, 2020 8:14 pm
- Forum: General Rate Laws
- Topic: Rate Law
- Replies: 2
- Views: 245
Re: Rate Law
The rate law isn't determined by the overall equation. Certain reactions might proceed in multiple steps. In this case, the rate is determined by the slowest step of the reaction, not the overall equation. HI is second order because the rate determining step is bimolecular with respect to HI (two HI...
- Thu Mar 05, 2020 8:10 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: instantaneous rate
- Replies: 16
- Views: 951
Re: instantaneous rate
Since reaction and product concentrations follow smooth curves that are defined by equations, we can easily use the instantaneous rate of change, which will give us a more accurate result than using an average. It also allows us to turn the differential rate laws into the integrated rate laws.
- Thu Mar 05, 2020 8:09 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Study Advice
- Replies: 73
- Views: 6863
Re: Study Advice
Lyndon's review sessions are always super helpful. Do his packet before attending the session. Other than that, probably do a lot of practice problems from the homeworks and make sure you know how to do everything.
- Thu Mar 05, 2020 8:04 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Week 9 Wednesday lecture
- Replies: 7
- Views: 425
Re: Week 9 Wednesday lecture
CO is not in the rate law because its concentration does not affect the rate of the reaction (i.e. it is zero order). This implies that CO is not involved in the slowest step of this multi-step reaction. It does not mean that CO is not involved in the reaction at all. Just that it's not significant ...
- Thu Mar 05, 2020 7:59 pm
- Forum: Zero Order Reactions
- Topic: order of reactions
- Replies: 4
- Views: 300
Re: order of reactions
Reaction rates are determined empirically by changing one reaction concentration at a time and observing the effect on the reaction rate. If you double the initial concentration of A and the rate does not change, A is zero order. If the rate doubles, A is first order. If the rate quadruples, then A ...
- Mon Feb 24, 2020 12:21 pm
- Forum: Balancing Redox Reactions
- Topic: Reduction?
- Replies: 13
- Views: 632
Re: Reduction?
Calculate the oxidation number of the compounds before and after the reaction. e.g. if MnO4- becomes Mn2+, then the reactant Mn has an oxidation number of 7+ (each oxygen has a charge of -2, and there are 4 of them. The manganese needs to be +7 to bring the overall charge to -1), and the product Mn ...
- Mon Feb 24, 2020 12:14 pm
- Forum: Balancing Redox Reactions
- Topic: Determining direction of flow
- Replies: 15
- Views: 779
Re: Determining direction of flow
Electrons always flow from the reaction that is losing electrons (i.e. oxidation), which occurs at the anode, to the reaction that is gaining electrons (i.e. reduction), which occurs at the cathode.
- Mon Feb 24, 2020 12:07 pm
- Forum: Balancing Redox Reactions
- Topic: OIL RIG
- Replies: 4
- Views: 301
Re: OIL RIG
This is the one I learned for AP chem
the RED CAT LEO says GRR at AN OX
RED CAT: reduction occurs at the cathode
LEO: loss of electrons is oxidation
GRR: gain of electrons is reduction
AN OX: oxidation occurs at the anode
the RED CAT LEO says GRR at AN OX
RED CAT: reduction occurs at the cathode
LEO: loss of electrons is oxidation
GRR: gain of electrons is reduction
AN OX: oxidation occurs at the anode
- Mon Feb 24, 2020 12:01 pm
- Forum: Balancing Redox Reactions
- Topic: Platinum in cell diagram
- Replies: 10
- Views: 737
Re: Platinum in cell diagram
You need a solid metal to conduct the flow of electrons when both compounds of your anode or cathode are in aqueous solution. Platinum is used when it is not involved in the chemistry of the galvanic cell, and therefore will not be oxidized or reduced while acting as a conducting metal.
- Mon Feb 24, 2020 12:00 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing/Reducing Agent
- Replies: 8
- Views: 595
Re: Oxidizing/Reducing Agent
The oxidizing agent is the compound that becomes reduced. The reducing agent is the compound that becomes oxidized. I remember it this way: The reducing agent is the compound that starts off reduced and causes the other compound to become oxidized. The oxidizing agent is the compound that starts off...
- Tue Feb 18, 2020 10:42 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Temperature Dependence of K
- Replies: 3
- Views: 245
Re: Temperature Dependence of K
Just because ΔΗ is constant doesn't mean it's not an important part of the equation. We are able to factor it out because it's not changing, but since its value can be something other than 1, we cannot eliminate it from the equation.
- Tue Feb 18, 2020 10:39 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Signs for Gibbs Free Energy
- Replies: 11
- Views: 689
Re: Signs for Gibbs Free Energy
When ΔG is positive, the reaction is non-spontaneous and requires an input of energy to proceed towards the products. When ΔG is negative, the reaction is spontaneous and releases energy as it proceeds towards the products.
- Tue Feb 18, 2020 10:37 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Free Energy and Work
- Replies: 5
- Views: 402
Re: Free Energy and Work
The released free energy is the maximum amount of energy that can be used as work. In reality, it can't all be perfectly utilized, but we calculate it that way.
- Wed Feb 12, 2020 12:17 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Pizza Rolls 6 (pt.1)
- Replies: 10
- Views: 734
Re: Pizza Rolls 6 (pt.1)
In this problem, delta S and delta U are equal to 0 when referring to the change in entropy/internal energy over the course of the entire process, which the question is asking for. Entropy and internal energy are state functions, meaning we can look at the initial and final states directly without ...
- Wed Feb 12, 2020 12:40 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Pizza Rolls 6 (pt.1)
- Replies: 10
- Views: 734
Re: Pizza Rolls 6 (pt.1)
In this problem, delta S and delta U are equal to 0 when referring to the change in entropy/internal energy over the course of the entire process, which the question is asking for. Entropy and internal energy are state functions, meaning we can look at the initial and final states directly without ...
- Tue Feb 11, 2020 10:28 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Pizza Rolls 10
- Replies: 4
- Views: 387
Re: Pizza Rolls 10
I did it the way you advised and still got 22.85C as my answer for Tf. For your Step 3, shouldn't the right side of the equation be negative (e.g. -265 g*specific heat of water...)? Why do you not use the specific heat of ice on the right side? (Using the specific heat of ice gives me 20.93C for my...
- Sat Feb 08, 2020 10:56 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible and Irreversible
- Replies: 3
- Views: 196
Re: Reversible and Irreversible
Because for infinitesimally small expansion, work must be done and equilibrium must be regained. This repeats over and over and this creates a decreasing curve where as irreversible expansion occurs immediately so work occurs instantly only once and equilibrium is only regained once (this creates a...
- Sat Feb 08, 2020 10:52 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible Reactions
- Replies: 3
- Views: 186
Re: Reversible Reactions
A reversible reaction is where products and reactants are being formed at the same time, and once the forward and reverse reactions occur at the same rate, they reach equilibrium. Not sure this applies in a thermodynamic setting. In my understanding, a reversible expansion is when the external pres...
- Sat Feb 08, 2020 10:17 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: degeneracy relation to thermo
- Replies: 5
- Views: 290
Re: degeneracy relation to thermo
Degeneracy is the number of all possible states of the particles in a system. It is used to calculate entropy.
- Sat Feb 08, 2020 10:15 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: irreversible vs reversible
- Replies: 3
- Views: 108
Re: irreversible vs reversible
In an irreversible expansion, the pressure of a system suddenly changes. In a reversible expansion, the pressure is slowly changed in infinitesimal increments (requires an integral).
- Sat Feb 08, 2020 9:51 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous Reaction
- Replies: 8
- Views: 387
Re: Spontaneous Reaction
When ΔG is negative, the reaction is spontaneous.
- Mon Feb 03, 2020 5:37 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated system
- Replies: 10
- Views: 1329
Re: Isolated system
Wait, but I assumed that heat would still technically be able to escape from a hydroflask to the surroundings. Are there any other examples that would be an isolated system? In reality, a hydroflask is a closed system. In theory, perfectly insulated thermos bottles would be isolated systems because...
- Mon Feb 03, 2020 5:32 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Specific heat capacity
- Replies: 7
- Views: 436
Re: Specific heat capacity
Specific Heat Capacity = Heat Capacity per gram of substance
Molar Heat Capacity = Heat Capacity per mole of substance
Molar Heat Capacity = Heat Capacity per mole of substance
- Mon Feb 03, 2020 5:30 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed Systems
- Replies: 14
- Views: 917
Re: Closed Systems
ΔU = q + w, so to change the energy of a closed system, you would heat it or do work on it.
- Mon Feb 03, 2020 5:25 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: closed vs isolated?
- Replies: 7
- Views: 1282
Re: closed vs isolated?
Closed systems don't allow the exchange of matter, but they do allow the exchange of energy. An isolated system is perfectly insulated, and does not allow the exchange of matter or energy.
- Mon Feb 03, 2020 5:23 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: examples of doing work
- Replies: 2
- Views: 150
Re: examples of doing work
One example would be an expanding gas pushing a piston.
- Sat Jan 25, 2020 11:51 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Phase Changes
- Replies: 4
- Views: 115
Re: Phase Changes
Because at a certain point, the energy input is not being used to raise the temperature, and is instead being used to change the phase of the molecules (i.e. break intermolecular interactions)
- Sat Jan 25, 2020 11:50 pm
- Forum: Phase Changes & Related Calculations
- Topic: State Function
- Replies: 7
- Views: 331
Re: State Function
Enthalpy is a state function because you can use the final and initial values as your only information to calculate the change in enthalpy. The path taken is not required information.
- Sat Jan 25, 2020 9:52 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Percent Ionization
- Replies: 12
- Views: 554
Re: Percent Ionization
You calculate the percent ionization by taking the concentration of H3O+ and dividing it by the initial concentration of the acid.
- Sat Jan 25, 2020 9:50 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Acid and Bases
- Replies: 4
- Views: 190
Re: Acid and Bases
First, set up an ICE table to determine the concentration of H3O+. Then take the negative log of that value to find the pH. Then subtract that value of pH from 14 to find the pOH.
- Sat Jan 25, 2020 9:47 pm
- Forum: Ideal Gases
- Topic: R Constant
- Replies: 26
- Views: 1142
Re: R Constant
The value of R you use depends on the units given to you in the problem and the units which your answer needs to be in. The units of R will cancel out with all of the given terms to give you your final answer's units.
- Sun Jan 19, 2020 5:35 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: ICE table
- Replies: 11
- Views: 352
Re: ICE table
An ICE table should be used when you are given initial concentrations and are asked to find concentrations, pH, or pOH at equilibrium. You should memorize the strong acids and strong bases.
- Sun Jan 19, 2020 5:33 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: pH vs. pOH
- Replies: 13
- Views: 403
Re: pH vs. pOH
You calculate pH and pOH by taking the negative log (-log) of [H3O+] or [OH-]. You typically calculate pH for acids and pOH for bases, but questions will often ask you for pH no matter what. Use pH+pOH=14 to convert from pOH to pH.
- Sun Jan 19, 2020 5:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: conjugate seesaw
- Replies: 4
- Views: 120
Re: conjugate seesaw
Ka x Kb = Kw
Kw is a constant (10^-14)
If Ka is high for a strong acid, Kb must therefore be low because their product is equal to a constant. And vice versa: if Kb is high for a strong base, then Ka must therefore be low.
Kw is a constant (10^-14)
If Ka is high for a strong acid, Kb must therefore be low because their product is equal to a constant. And vice versa: if Kb is high for a strong base, then Ka must therefore be low.
- Sun Jan 19, 2020 5:28 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: % Ionization
- Replies: 3
- Views: 105
Re: % Ionization
@AMahadi, if your Ka or Kb is small (<10^-3), then you are allowed to eliminate all x values in the equilibrium expression which follows the form (n-x). This makes calculating the value of x more simple. If the percent ionization of the acid or base is <5%, then this approximation is valid.
- Sun Jan 19, 2020 5:24 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: kA and kB
- Replies: 1
- Views: 61
Re: kA and kB
Ka x Kb = Kw (10^-14)
pKa + pKb = 14
pKa + pKb = 14
- Sat Jan 11, 2020 8:58 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Using the "ICE" box
- Replies: 8
- Views: 232
Re: Using the "ICE" box
Don't include solids and liquids in equilibrium calculations.
- Sat Jan 11, 2020 8:54 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Using Kc Vs Kp
- Replies: 22
- Views: 974
Re: Using Kc Vs Kp
If you're looking at aqueous equilibrium, use Kc. If looking at gasses, you can either use Kc or Kp. Use the question to determine the proper answer.
- Sat Jan 11, 2020 8:52 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Problem 5i.11- using molarity in place of pressure?
- Replies: 3
- Views: 177
Re: Problem 5i.11- using molarity in place of pressure?
You can either use partial pressure or concentration when calculating equilibrium for gasses.
- Sat Jan 11, 2020 8:51 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5.35
- Replies: 4
- Views: 146
Re: 5.35
Create an ICE table using the initial and final values for A B and C in the table. Then plug these values into the K expression.
- Sat Jan 11, 2020 8:45 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Difference between K and Q
- Replies: 6
- Views: 256
Re: Difference between K and Q
K is the ratio of the concentrations of the products and reactants when the reaction is at equilibrium. Q is the ratio of the concentrations of the products and reactants at any point in the reaction. Comparing K to Q will tell you which way the reaction will proceed.
- Tue Dec 03, 2019 8:13 pm
- Forum: Electronegativity
- Topic: Symbols for partial charge
- Replies: 4
- Views: 4428
Re: Symbols for partial charge
The +/- delta symbols represent partial positive and partial negative. The +-----> arrow points in the direction of the negative end of the dipole, with the "cross" end of the arrow towards the positive end of the dipole.
- Tue Dec 03, 2019 8:09 pm
- Forum: Amphoteric Compounds
- Topic: how to determine
- Replies: 3
- Views: 112
Re: how to determine
No. Take the amphoteric oxides as an example (e.g. Al2O3). If you react Al2O3 with a strong acid, it will act as a base by producing hydroxide ions. If you react Al2O3 with a strong base, it will act as an acid by producing hydronium ions. None of the amphoteric oxides contain hydrogen.
- Tue Dec 03, 2019 7:59 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Explain VSEPR conceptually
- Replies: 12
- Views: 790
Re: Explain VSEPR conceptually
VSEPR predicts the shapes of molecules by using the principle that regions of electron density around a central atom will tend to maximize their distance from one another. This principle leads to the various VSEPR geometries, such as trigonal bipyramidal, tetrahedral, etc. These shapes maximize the ...
- Tue Dec 03, 2019 7:57 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bent vs linear
- Replies: 56
- Views: 4124
Re: Bent vs linear
Bent molecules will have lone pairs on the central atom in addition to the two bound atoms. These lone pairs will distort the shape of the molecule to bent instead of linear.
- Tue Dec 03, 2019 7:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: T-shape
- Replies: 21
- Views: 1666
Re: T-shape
T shaped molecules have 3 bonded atoms and 2 lone pairs. The 5 regions of electron density have trigonal bipyramidal geometry, and the two lone pairs are placed equatorially to maximize distance; this forms a T shaped molecule.
- Tue Dec 03, 2019 7:53 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: pKa vs Ka
- Replies: 6
- Views: 466
Re: pKa vs Ka
For the following acid equilibrium :
HA <----> H+ + A-
Ka = [H+][A-]/[HA]
pKa = -log[Ka]
HA <----> H+ + A-
Ka = [H+][A-]/[HA]
pKa = -log[Ka]
- Tue Dec 03, 2019 7:50 pm
- Forum: Polyprotic Acids & Bases
- Topic: How can you tell
- Replies: 18
- Views: 961
Re: How can you tell
If an acid has more than one hydrogen which it can dissociate, it is polyprotic.
- Mon Dec 02, 2019 10:34 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Pka vs Ka
- Replies: 10
- Views: 576
Re: Pka vs Ka
For the following reaction:
HA ---> H+ + A-
Ka = [H+][A-]/[HA]
pKa = -log(Ka)
For stronger acids, Ka will be high and pKa will be low, and vice versa.
HA ---> H+ + A-
Ka = [H+][A-]/[HA]
pKa = -log(Ka)
For stronger acids, Ka will be high and pKa will be low, and vice versa.
- Mon Dec 02, 2019 10:32 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Inorganic or Organic
- Replies: 6
- Views: 446
Re: Inorganic or Organic
Organic = Carbon. Therefore, organic acids have carbon while inorganic acids do not.
- Mon Dec 02, 2019 10:31 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Difference between weak acids/bases and strong acids/bases
- Replies: 6
- Views: 391
Re: Difference between weak acids/bases and strong acids/bases
Strong acids fully ionize (i.e. dissociate into products), while weak acids only partially dissociate and require equilibrium calculations to determine concentrations etc.
- Mon Dec 02, 2019 10:30 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Strong Acids
- Replies: 3
- Views: 174
Re: Strong Acids
The Ka is equal to the product of the concentrations of the products divided by the product of the concentrations of the reactants. e.g.: HA ---> H+ + A- Ka = [H+][A-]/[HA] Stronger acids more readily dissociate into their products. Therefore, the stronger the acid, the higher the Ka because the con...
- Mon Dec 02, 2019 10:25 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Acids Vs. Bases
- Replies: 11
- Views: 864
Re: Acids Vs. Bases
Acids typically lose H+ while bases typically gain them.
- Mon Dec 02, 2019 10:23 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Strength of Acids - Example from Lecture
- Replies: 6
- Views: 465
Re: Strength of Acids - Example from Lecture
CCl3COOH and CH3COOH have the anions CCl3COO- and CH3COO- respectively. The former anion is more stable than the latter because the 3 chlorines delocalize the negative charge on the oxygen. Oxoacids will be more acidic if the resulting anion is stabilized by electronegative atoms which delocalize th...
- Mon Dec 02, 2019 10:19 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Trichloroacetic acid
- Replies: 2
- Views: 97
Re: Trichloroacetic acid
The resulting anion of trichloroacetic acid is more stable than that of acetic acid because the three chlorines delocalize the negative charge on the oxygen, whereas in acetic acid, the charge is not as delocalized. Oxoacids which have more stable anions will be more acidic.
- Mon Dec 02, 2019 10:15 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Amphoteric compounds
- Replies: 4
- Views: 157
Re: Amphoteric compounds
Amphoteric compounds can have both acidic and basic character. (e.g. H2O can become H3O+ or OH-)
Dr. Lavelle pointed out in class the diagonal band of amphoteric oxides (Be, Al, Ga, Sn, Sb, Pb), quite similar to the band of metalloids. All of these oxides (e.g. Al2O3) are amphoteric.
Dr. Lavelle pointed out in class the diagonal band of amphoteric oxides (Be, Al, Ga, Sn, Sb, Pb), quite similar to the band of metalloids. All of these oxides (e.g. Al2O3) are amphoteric.
- Mon Dec 02, 2019 10:11 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: neutralization
- Replies: 4
- Views: 254
Re: neutralization
Neutralization reactions form water and a salt as their products.
- Mon Dec 02, 2019 10:08 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Lecture
- Replies: 3
- Views: 322
Re: Lecture
Compare the acids HClO and HBrO. Their resulting anions will be ClO- and BrO- respectively. ClO- will be more stable than BrO for the following reason: Chlorine and Bromine are both considered "electron-withdrawing atoms" because of their electronegativity, and they will have the effect of...
- Mon Dec 02, 2019 10:03 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Electronegativity and acid strength
- Replies: 5
- Views: 269
Re: Electronegativity and acid strength
Oxoacids will be more acidic if the anion formed is stabilized by electronegative atoms which delocalize the negative charge. Chlorine is more electronegative than bromine, which means it will more effectively delocalize the negative charge on the oxygen, yielding a more stable anion – this causes i...
- Mon Dec 02, 2019 10:03 am
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Electronegativity and acid strength
- Replies: 2
- Views: 127
Re: Electronegativity and acid strength
Oxoacids will be more acidic if the anion formed is stabilized by electronegative atoms which delocalize the negative charge. Chlorine is more electronegative than bromine, which means it will more effectively delocalize the negative charge on the oxygen, yielding a more stable anion – this causes i...
- Fri Nov 15, 2019 1:09 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Remembering Molecular Geometric Shapes
- Replies: 2
- Views: 152
Re: Remembering Molecular Geometric Shapes
https://lh6.googleusercontent.com/fH1A2_-wM47qFR8X69w6002x-Iw75lx2Lxh6WiY4oTErTr2YyOOluabl5HuJ0usijqiz1QxAQSuuXIDl67mF1AwouYEiNtxQgShsJWJkDqEhFOoSuTIM5ORfbP9O You could memorize, the 5 "parent" shapes (linear, trigonal pyramidal, tetrahedral, trigonal bipyramidal, octahedral), and then in...
- Fri Nov 15, 2019 1:04 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Determining Bond Angle
- Replies: 3
- Views: 256
Re: Determining Bond Angle
Not always. For example, in square planar molecules, the bond angles are still 90 degrees because the axial lone pairs directly oppose each other. Another example would be linear molecules with three equatorial lone pairs: the bond angle is still 180 degrees.
- Fri Nov 15, 2019 1:00 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Geometry vs Electron Geometry
- Replies: 2
- Views: 133
Re: Molecular Geometry vs Electron Geometry
The electron geometry is the arrangement of the regions of electron density (lone pairs + bonding regions) around the central atom. The molecular geometry is the shape of the molecule, which is only determined using the bonding regions. For example, the electron geometry of H2O is tetrahedral becaus...
- Fri Nov 15, 2019 12:55 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: bond angles
- Replies: 9
- Views: 597
Re: bond angles
Lone pairs have greater repulsion strength than bonding regions do. So lone pairs will tend to push bonding regions closer together, making the bond angles "a little less then" their typical value. For example, if you have a tetrahedral with 1 lone pair, the three bonding regions will have...
- Fri Nov 15, 2019 12:54 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Octahedral
- Replies: 5
- Views: 388
Re: Octahedral
All three have the 6 regions of electron density arranged as an octahedral. The difference is in the number of lone pairs and the number of bonding regions. If the molecular shape is an octahedral, then it has 6 bonding regions (i.e. 6 atoms bound to the central atom). If the molecular shape is squa...
- Fri Nov 15, 2019 12:48 am
- Forum: Hybridization
- Topic: Pi and Sigma Bonds
- Replies: 17
- Views: 1233
Re: Pi and Sigma Bonds
Every bond after the first is a pi bond. (i.e. single bond = 1 sigma ; double bond = 1 sigma & 1 pi ; triple bond = 1 sigma & 2 pi)
- Mon Nov 11, 2019 11:17 pm
- Forum: Lewis Structures
- Topic: Drawing Lewis Structures
- Replies: 18
- Views: 650
Re: Drawing Lewis Structures
As others have said, formal charges must add up to the overall charge of the molecule you are drawing. However, when it comes to determining which atom(s) gets the non-zero formal charge(s), use electronegativity. For example, if you draw the lewis structure for the chlorate ion (ClO3-), when decidi...
- Mon Nov 11, 2019 11:12 pm
- Forum: Lewis Structures
- Topic: Lewis structures that are not symmetrical
- Replies: 4
- Views: 572
Re: Lewis structures that are not symmetrical
It depends on the molecule. When you arrange 5 identical atoms around a central atom (e.g. PF5), this molecule will be non-polar because of the shape of the molecule. You can also have a symmetrical molecule that is polar (e.g. CH2Cl2) due to dipole moments etc.. Symmetry is not a reliable way to de...
- Mon Nov 11, 2019 11:02 pm
- Forum: Lewis Structures
- Topic: Center of a Lewis Structure
- Replies: 7
- Views: 508
Re: Center of a Lewis Structure
Yes. Lavelle said in lecture that this is the best way of going about drawing lewis structures for this class.
- Mon Nov 11, 2019 10:56 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: melting points
- Replies: 6
- Views: 287
Re: melting points
Hydrogen bonds are stronger than dipole/dipole or induced dipole/induced dipole interactions. H2O has the ability to hydrogen bond with itself because of the H-O bond, while H2S cannot. This accounts for H2O's higher melting point.
- Mon Nov 11, 2019 10:53 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: Homework 3F.5 Part C
- Replies: 2
- Views: 141
Re: Homework 3F.5 Part C
CHI3 is a much larger molecule than CHF3, because the size of Iodine's electron cloud is much larger than the size of Fluorine's. The larger the molecule (by molar mass and by size), the greater its polarizability and therefore the greater its LDFs (induced dipole/induced dipole)
- Sun Nov 03, 2019 11:50 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Differences between polarizing power and polarizablity
- Replies: 2
- Views: 155
Re: Differences between polarizing power and polarizablity
Cations have polarizing power because their positive charge distorts the electron cloud of the anion. Likewise, anions have polarizability because their electron cloud can be distorted by positively charged cations. The greater the charge on the cation (Al3+ is a good example), the higher its polari...
- Sun Nov 03, 2019 11:46 pm
- Forum: Lewis Structures
- Topic: Drawing lewis structures
- Replies: 5
- Views: 212
Re: Drawing lewis structures
Try and minimize your formal charges whenever you draw a Lewis structure, because this means that you have likely found the most stable structure.
- Sun Nov 03, 2019 11:44 pm
- Forum: Lewis Structures
- Topic: formal charge
- Replies: 6
- Views: 277
Re: formal charge
Formal charges are a useful quick check to see if your Lewis Structure is stable or still needs reworking. I would recommend quickly checking formal charges on most lewis structures you draw for this reason, unless it's ridiculously easy or it's a structure you know already.
- Sun Nov 03, 2019 8:30 pm
- Forum: DeBroglie Equation
- Topic: Dino Nuggets Problem 6a
- Replies: 2
- Views: 333
Re: Dino Nuggets Problem 6a
Actually I figured it out, but I'm going to keep this here in case anyone else is confused. The power of 10 is off by 3 because I forgot to convert grams to kilograms...
- Sun Nov 03, 2019 8:27 pm
- Forum: DeBroglie Equation
- Topic: Dino Nuggets Problem 6a
- Replies: 2
- Views: 333
Dino Nuggets Problem 6a
(Problem: A new element GarBreadium is discovered to have molar mass 3.157 g∙mol-1. The GarBreadium atom travels at an average speed of 1.35x103 m∙s-1 at room temperature. What is the average wavelength of the GarBreadium atom at room temperature?) My answer for this problem comes out to 9.36x10^-14...
- Sun Oct 27, 2019 10:27 pm
- Forum: Lewis Structures
- Topic: Choosing the central atom
- Replies: 16
- Views: 762
Re: Choosing the central atom
The atom with the lowest ionization energy should be the central atom. When a molecule contains carbon, it is usually central in some way. Hydrogen should never be chosen as the central atom.
- Sun Oct 27, 2019 10:23 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal charge purpose
- Replies: 40
- Views: 7091
Re: Formal charge purpose
Formal charges also allow you to compare different possible lewis structures for the same molecule. For example, if the oxygen atoms in one lewis structure have positive formal charges and negative formal charges in another, the second lewis structure is probably preferable (assuming that other fact...
- Sun Oct 27, 2019 10:20 pm
- Forum: Sigma & Pi Bonds
- Topic: Double bond
- Replies: 15
- Views: 557
Re: Double bond
Add double bonds to a lewis structure when you still need to satisfy the octet rule after adding your valence electrons, or if it gives the molecule better formal charges.
- Sun Oct 27, 2019 10:17 pm
- Forum: Lewis Structures
- Topic: Choosing the central atom
- Replies: 16
- Views: 762
Re: Choosing the central atom
The atom with the lowest ionization energy should be the central atom.
- Sun Oct 27, 2019 10:14 pm
- Forum: Ionic & Covalent Bonds
- Topic: What is the difference between an anion and cation?
- Replies: 7
- Views: 843
Re: What is the difference between an anion and cation?
An anion is an ion with a negative charge and a cation is an ion with a positive charge. (The way I remember this is that the "t" in cation looks like a plus sign which makes it positively charged.)
- Sun Oct 20, 2019 9:10 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: magnetic quantum #
- Replies: 3
- Views: 155
Re: magnetic quantum #
Different subscripts for different orbitals (e.g. px, py, pz, dxy, dyz, dxy, etc.) are just different labels for the possible orientations of the orbitals of a certain shape, based on the coordinate system you are using. In other words, for ml = -1, 0, 1, it is arbitrary which one you label as px, p...
- Sun Oct 20, 2019 9:02 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Pauli Exclusion Principle
- Replies: 9
- Views: 902
Re: Pauli Exclusion Principle
No two electrons may have the same 4 quantum numbers. i.e. two electrons in the same orbital must have opposite spins. It is not possible for them to have the same spin.
- Sun Oct 20, 2019 8:59 pm
- Forum: Trends in The Periodic Table
- Topic: Trends in Electron Affinity
- Replies: 3
- Views: 222
Re: Trends in Electron Affinity
Electron affinity tends to increase as atoms get more electronegative, i.e. moving up and to the right on the periodic table.
- Sun Oct 20, 2019 8:54 pm
- Forum: Trends in The Periodic Table
- Topic: Atomic Radius
- Replies: 16
- Views: 910
Re: Atomic Radius
You should only compare atomic radii of atoms in their ground state.
- Sun Oct 20, 2019 8:52 pm
- Forum: Trends in The Periodic Table
- Topic: Atomic radii
- Replies: 9
- Views: 517
Re: Atomic radii
As you move right across a row in the periodic table, the positive charge of the nucleus becomes greater due to the increasing number of protons. This causes the nucleus to have a greater pull on the electrons, thereby decreasing the atomic radius. This is the effect of effective nuclear charge.
- Sat Oct 12, 2019 5:21 pm
- Forum: Empirical & Molecular Formulas
- Topic: post test problem
- Replies: 3
- Views: 450
Re: post test problem
Yes, understanding conservation of mass is key to solving this problem. The amount of Cobalt is unchanged in the reactants and products, so to find the mass of Fluorine used, you need to subtract the mass of Cobalt (339.20 g) from the final mass of the products (996.08), which you can use to solve t...
- Sat Oct 12, 2019 5:17 pm
- Forum: Significant Figures
- Topic: Question About Significant Figures and Rounding
- Replies: 22
- Views: 3199
Re: Question About Significant Figures and Rounding
Don't worry about significant figures until it's time to write your final answer to the problem. While solving the problem, numbers should remain as exact as possible so that your final answer is as accurate as it can be. Then apply significant figure rules to your final answer.
- Sat Oct 12, 2019 5:14 pm
- Forum: Significant Figures
- Topic: Answer being a tad bit off
- Replies: 8
- Views: 546
Re: Answer being a tad bit off
Try to avoid rounding the numbers you use for your calculation, and only round at the end of the problem. Excess rounding while solving a problem leads to significant discrepancies between your answer and the correct answer.
- Sat Oct 12, 2019 5:11 pm
- Forum: Limiting Reactant Calculations
- Topic: Test 1 Calculator
- Replies: 6
- Views: 398
Re: Test 1 Calculator
In addition, many new graphing calculators have systems of equations solvers which significantly cuts down the time required to solve certain problems later on in the course.