Search found 100 matches
- Sat Mar 14, 2020 10:17 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: intermediates
- Replies: 8
- Views: 546
Re: intermediates
In a multi-step reaction, there are intermediates. They are something that forms in an earlier step, but are ultimately used as a reactant in a subsequent step. Thus, they are cancelled out in the net/final equation. They are essential to the mechanism of the reaction, but do not end up in the final...
- Sat Mar 14, 2020 10:16 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 5
- Views: 353
Re: Catalysts
Catalysts are no consumed as they appear as an input, but also an output of a reaction. Thus, the amount of catalyst is not decreased by lowering the activation energy.
- Sat Mar 14, 2020 10:14 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalyst's effect on overall reaction
- Replies: 7
- Views: 448
Re: Catalyst's effect on overall reaction
In order to consider this reaction, you have to know that the slow step is the rate determining step. If you make the other steps faster, it still does not change the fact that the slow step is still at the same (slow) rate. As the slow step is the sole factor you consider when determining overall r...
- Sat Mar 14, 2020 10:12 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 8
- Views: 478
Re: Catalysts
Homogeneous catalysts are the same state as the reactants, while heterogeneous catalysts are in a different state. With heterogeneous catalysts, the reactants sit on the surface of the catalyst.
- Sat Mar 14, 2020 10:09 am
- Forum: *Enzyme Kinetics
- Topic: Heterogeneous catalyst
- Replies: 3
- Views: 424
Re: Heterogeneous catalyst
Absorption is different from adsorption. In adsorption, the reactants sit on the surface of the catalyst. So thus, I'd believe you'd visualize it as liquid reactants in a pool on top of a solid or gas surrounding the surface of the solid.
- Sun Mar 08, 2020 5:43 pm
- Forum: General Rate Laws
- Topic: the variable A
- Replies: 4
- Views: 322
Re: the variable A
A was described in class as the frequency factor or pre-exponential factor (includes # of collisions with correct orientation)
- Sun Mar 08, 2020 5:39 pm
- Forum: General Rate Laws
- Topic: derivations?
- Replies: 5
- Views: 387
Re: derivations?
I don't think he will actually ask us to derive something on the test. Although, knowing how to derive the equations is listed on the outline for the Kinetics section, so I would be familiar enough with them to manipulate the equations.
- Sun Mar 08, 2020 5:35 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: derivations
- Replies: 9
- Views: 577
Re: derivations
On the Kinetics outline Lavelle lists: Know how to derive the differential and integrated rate laws for zero, 1st and 2nd order reactions Use the Arrhenius equation and rate constants measured at different temperatures to determine activation energy. Use the Arrhenius equation and the activation ene...
- Sun Mar 08, 2020 5:32 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: kinetically stable?
- Replies: 10
- Views: 707
Re: kinetically stable?
To be stable, the reaction will have a negative deltaG value, so it is technically spontaneous. Although, there is a very large activation energy which prevents it from proceeding. Thus, it is kinetically trapped in reactant form.
- Sun Mar 08, 2020 5:30 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: instantaneous rate
- Replies: 16
- Views: 938
Re: instantaneous rate
An instantaneous rate provides an infinite amount of time points that you can measure the rate. It is more accurate than taking the average between two points because you are looking at the exact rate in time, rather than an approximation between two points where the rate in between the two points c...
- Sun Mar 01, 2020 4:21 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Values of Standard Electrode Potentials
- Replies: 4
- Views: 356
Re: Values of Standard Electrode Potentials
A negative E values means that the reaction is not spontaneous, while if the E value is positive, then the reaction is spontaneous. You can see this connection through the relation of delta G= -nFE.
- Sun Mar 01, 2020 4:17 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: ∆G and ∆G°
- Replies: 7
- Views: 511
Re: ∆G and ∆G°
∆G° is for standard conditions, which ∆G is for non-standard conditions. Therefore, the principle still remains that a negative deltaG would mean that the reaction is spontaneous.
- Sun Mar 01, 2020 4:13 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Flipping the sign
- Replies: 10
- Views: 605
Re: Flipping the sign
Tabled values are typically given in terms of reduction. In order to calculate the entire redox reaction value, you must flip the sign on the half reaction that is showing oxidation.
- Sun Mar 01, 2020 4:08 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: finding n
- Replies: 6
- Views: 431
Re: finding n
n stands for the number of electrons transferred. You find this value by balancing the two half reactions in a redox situation. Once you balance them, you look at the electron transfer and use that value as n.
- Sun Mar 01, 2020 4:02 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 10
- Views: 482
Re: Salt Bridge
A salt bridge allows ion transfer to occur. This allows the electrons to keep flowing and maintain a neutral charge. When you don't have a salt bridge, there is another form of ion transfer, such as through a porous disk.
- Sun Feb 23, 2020 8:25 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Half reactions
- Replies: 13
- Views: 725
Re: Half reactions
A half reaction shows either the oxidation or reduction of elements, and thus shows the relative transfer of electrons. It is useful because it allows us to balance the electrons in a redox reaction.
- Sun Feb 23, 2020 8:23 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cathode vs Anode
- Replies: 11
- Views: 887
Re: Cathode vs Anode
The cathode is where the reduction reaction takes place in a salt bridge circuit. It is usually designated on the right side of the diagram. Conversely, the anode is where the oxidation occurs and is usually found on the left side of the diagram.
- Sun Feb 23, 2020 8:18 pm
- Forum: Balancing Redox Reactions
- Topic: Half Reactions
- Replies: 12
- Views: 827
Re: Half Reactions
A half reaction is used when trying to balance a redox reaction for our purposes. One of the half reaction shows the oxidation, while the other demonstrates the reduction. This equations allow you to keep track of the electrons being transferred in order to balance the equation properly.
- Sun Feb 23, 2020 8:17 pm
- Forum: Balancing Redox Reactions
- Topic: Steps
- Replies: 7
- Views: 410
Re: Steps
Balancing a redox reaction is a bit different than just comparing normal products and reactants. Here you must keep track of the electrons being transferred. You must balance the two half reactions (one for oxidation, one for reduction) in terms of the electrons as well as the other elements. Thus, ...
- Sun Feb 23, 2020 8:13 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: rust
- Replies: 9
- Views: 715
Re: rust
Rusting itself is a redox reaction, where the iron is oxidized, losing electrons, and oxygen is reduced, gaining electrons. Rust's chemical formula is Fe2O3.
- Sun Feb 16, 2020 9:10 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Differences in (delta)G^o equations
- Replies: 3
- Views: 182
Re: Differences in (delta)G^o equations
lnQ is used when the system is not at equilibrium, while lnK is found at equilibrium. If you think about it, Q = K at equilibrium, so you can see the connection.
- Sun Feb 16, 2020 9:08 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibb's Free Energy
- Replies: 7
- Views: 345
Re: Gibb's Free Energy
Gibbs Free Energy is the amount of thermodynamic potential energy available to do work. The equation for it is usually used to determine the energetics of a system, such as if it is spontaneous (Negative deltaG) or not.
- Sun Feb 16, 2020 9:06 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 5
- Views: 288
Re: Gibbs free energy
The degree symbol is to show that the value was found under standard conditions, while the deltaG without the degree symbol will be total change in Gibbs Free Energy, and not restricted to solely standard conditions.
- Sun Feb 16, 2020 9:04 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Why are exothermic reactions generally spontaneous?
- Replies: 16
- Views: 1150
Re: Why are exothermic reactions generally spontaneous?
Here you must consider the equation for Gibbs Free Energy, which is deltaG = deltaH - TdeltaS. A negative deltaG denotes a spontaneous reaction, while a negative deltaH denotes an exothermic reaction. You can see that in order to make deltaG negative, having a negative deltaH can help, as then the d...
- Sun Feb 16, 2020 8:59 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Midterm Curve
- Replies: 45
- Views: 2164
Re: Midterm Curve
The class is point based, so tests are not curved by themselves. The class as a whole is curved or adjusted. In order to pass the class, you must receive half of the available points.
- Sun Feb 09, 2020 10:16 pm
- Forum: Calculating Work of Expansion
- Topic: Isobaric and Isochoric
- Replies: 5
- Views: 367
Re: Isobaric and Isochoric
I believe knowing these terms would be important background to know regarding various changes to a system through temperature, pressure, etc
Here is a link to a discussion with these terms defined and a few more: viewtopic.php?f=128&t=9661
Here is a link to a discussion with these terms defined and a few more: viewtopic.php?f=128&t=9661
- Sun Feb 09, 2020 6:37 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Spontaneous vs Favorable
- Replies: 8
- Views: 414
Re: Spontaneous vs Favorable
I believe that favorable and spontaneous are used interchangeably. Both mean that a reaction will proceed without an input of energy.
- Sun Feb 09, 2020 6:31 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 4
- Views: 227
Re: Gibbs free energy
Gibbs free energy is the energy in a chemical reaction that can be used to do work. Since enthalpy is the total heat content of a system, you would subtract entropy, which is the unavailable energy that is used for work, with temperature. This gives us the energy that can be used for work. So to cl...
- Sun Feb 09, 2020 6:19 pm
- Forum: Calculating Work of Expansion
- Topic: units
- Replies: 3
- Views: 100
Re: units
1 L*atm is equal to 101.325 J, which allows you to compare various amounts of work.
- Sun Feb 09, 2020 6:06 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Pizza Rolls - State Functions
- Replies: 5
- Views: 277
Re: Pizza Rolls - State Functions
I believe it was "When you're under DePressed, you want to watch TV and get HUGS."
Which comes out at PD TV HUGS (Pressure, density, temperature, volume, enthalpy, internal energy, free energy, and entropy)
Which comes out at PD TV HUGS (Pressure, density, temperature, volume, enthalpy, internal energy, free energy, and entropy)
- Sat Feb 01, 2020 10:17 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Enthalpy vs. Heat
- Replies: 6
- Views: 228
Re: Enthalpy vs. Heat
Heat is defined to be the transfer of energy due to a temperature difference. Enthalpy was defined to be the heat released or absorbed in chemical reactions and physical changes at a constant pressure.
- Sat Feb 01, 2020 10:13 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Work
- Replies: 6
- Views: 200
Re: Work
Work can be positive or negative, depending on how you look at it. If you compress a piston, there is positive work being done on the system, as there was an input of work to move the piston. Conversely, the work done by the system is negative.
- Sat Feb 01, 2020 10:02 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed vs isolated systems
- Replies: 24
- Views: 861
Re: Closed vs isolated systems
The main difference between a closed system and an isolated system revolves around energy. Both closed and isolated systems do not exchange matter (reactants/products) with the surroundings, but closed systems exchange energy with the outside world. Isolated systems do not exchange mass OR energy. T...
- Sat Feb 01, 2020 9:58 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: isolated system
- Replies: 13
- Views: 609
Re: isolated system
If you think about the definition of an isolated system, nothing can interact with the surroundings (reactants, products, or energy). Thus, I like to think of it like a very very good thermos. If you leave hot water in it, an isolated system will keep the water heated through insulating the system a...
- Sat Feb 01, 2020 9:55 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed Systems
- Replies: 8
- Views: 392
Re: Closed Systems
Closed systems are still allowed to exchange energy with the outside world, while isolated systems are not. This is caused by the "isolating" factor of insulation. If you think about a really good thermos or bomb calorimeter, all of the energy should be stored and maintained in the vessel ...
- Sun Jan 26, 2020 11:16 am
- Forum: Phase Changes & Related Calculations
- Topic: State Function
- Replies: 7
- Views: 316
Re: State Function
Enthalpy is a state function because it only relies on the final and initial values to calculate it. If you use the example of altitude gain while rock climbing, the difference between the final and initial values is the same, regardless of what path you take. Conversely, a path function or non-stat...
- Sun Jan 26, 2020 11:12 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess's Law
- Replies: 2
- Views: 123
Re: Hess's Law
In lecture, Lavelle was able to add the reactions because it used an intermediate that allowed the two to be combined. N2 (g) + O2 (g) -> 2 NO (g) where delta H = 180kJ 2 NO (g) + O2 (g) -> 2 NO2 (g) where delta H = -122kJ Thus adding them to form a net equation N2 (g) + 2 O2 (g) -> 2NO2 (g) where d...
- Sun Jan 26, 2020 11:05 am
- Forum: Phase Changes & Related Calculations
- Topic: Steam vs Water
- Replies: 6
- Views: 211
Re: Steam vs Water
Steam produces a more severe burn than water because it has more energy, even though the two may have the same temperature. http://ibalchemy.com/wp-content/uploads/2015/11/Change-of-State-Water-graph.png You can see in this graph that although the temperature of steam and water may be the same, the ...
- Sun Jan 26, 2020 10:59 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: state functions
- Replies: 4
- Views: 132
Re: state functions
A state function is a property that is not dependent on path taken to obtain that state, thus these state properties can be added or subtracted. Some examples given in lecture were E, P, V, T, Density, and Heat Capacity. To further explain this using volume, if you compress a gas in a container usin...
- Sun Jan 26, 2020 10:50 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Using Bond Enthalpies
- Replies: 2
- Views: 86
Re: Using Bond Enthalpies
As mentioned in lecture, the general table of bond enthalpies shows all positive values. In order to determine the correct net reaction enthalpy as seen in method 2, you must convert the appropriate values to negative. (Reactants = positive energy required) --> (Products, energy is released = negati...
- Sun Jan 19, 2020 2:42 pm
- Forum: Ideal Gases
- Topic: Topics on Test 1
- Replies: 37
- Views: 1303
Re: Topics on Test 1
Based off of the syllabus, it appears that it would cover the first two topics/section (chemical equilibrium and acid/base equilibrium). In sum, it is the material covered in lecture up until Wednesday, because in class Friday Lavelle went over example problems.
- Sun Jan 19, 2020 2:38 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Test 1
- Replies: 6
- Views: 317
Re: Test 1
To answer Alison's question, I am reviewing by re-doing the practice modules on the website, answering all of the textbook practice problems, and reading the assigned textbook pages. Usually that gives me enough repetition to be able to find my weak spots in understanding, which I address in office ...
- Sun Jan 19, 2020 2:35 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Endothermic vs. exothermic
- Replies: 5
- Views: 211
Re: Endothermic vs. exothermic
With endothermic reactions, I think of heat as a reactant. Thus, if you apply the logic learned with Le Chatelier's principle, the equilibrium will shift to the right, just as it would if you had added a chemical reactant.
- Sun Jan 19, 2020 2:29 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Change in Amount of P/R?
- Replies: 2
- Views: 74
Re: Change in Amount of P/R?
K stays constant, no matter the amount/concentration of a product or a reactant added within a given reaction. K, rather, simply describes to concentration ratios of the products and reactants when the reaction has reached equilibrium. No matter the relative initial concentrations, a reaction will m...
- Sun Jan 19, 2020 2:25 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Difference between K and Q?
- Replies: 11
- Views: 523
Re: Difference between K and Q?
Q and K are actually calculated using the same formula with products over reactants. The difference between the two lies in when they apply. K ONLY applies to when a reaction has reached equilibrium. On the other hand, Q can represent any time during a reaction. Using Q, you an determine if the reac...
- Sat Jan 11, 2020 11:01 pm
- Forum: Ideal Gases
- Topic: Ideal Gas Law
- Replies: 6
- Views: 176
Re: Ideal Gas Law
To address Daniel's question, the Ideal Gas law only applies to ideal gases. An ideal gas is one where all of the collisions are perfectly elastic. Most common gases interact in this manner most of the time, but under certain conditions (including low temperature/high pressure), gases can begin to a...
- Sat Jan 11, 2020 10:52 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Quadratic Equation
- Replies: 3
- Views: 102
Re: Quadratic Equation
The quadratic equation is used to solve quadratics in the form of ax^2 + bx + c = 0. The a is the coefficient in front of the x^2 term, b is the coefficient of the x term, and c is a constant. The quadratic equation allows you to solve for x in equations where there are x terms raised to the second ...
- Sat Jan 11, 2020 10:46 pm
- Forum: Ideal Gases
- Topic: Q and K
- Replies: 2
- Views: 88
Re: Q and K
K is used to represent of products and reactants in a reaction that has reached equilibrium. Q, on the other hand, is calculated the same way as K, but using non-equilibrium concentrations of the reactants and products. Comparing Q to K allows you to [censored] what direction the reaction is moving ...
- Sat Jan 11, 2020 10:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Different K's
- Replies: 5
- Views: 288
Re: Different K's
I believe the Kc and Kp stand for Kc (concentration) and Kp (pressure) respectively. Thus you can use Kc or Kp for gases, as they can be represented as either, but for aqueous solutions you can only denote them using concentration (Kc)
- Sat Jan 11, 2020 10:36 pm
- Forum: Ideal Gases
- Topic: PV = nRT
- Replies: 16
- Views: 1843
Re: PV = nRT
The ideal gas law equation (PV=nRT) uses Pressure (P), Volume (V), number of moles (n), a universal gas constant (R), and Temperature (T)
- Sat Dec 07, 2019 2:02 pm
- Forum: Hybridization
- Topic: Lone pairs
- Replies: 4
- Views: 328
Re: Lone pairs
Lone pairs do count. If you think about how we define hybridization, it is through the electron geometry found in the VSEPR Theory. In order to find this electron geometry, we must count both the number of bonds and the number of lone pair sites in order to find the total number of areas of electron...
- Sat Dec 07, 2019 1:58 pm
- Forum: SI Units, Unit Conversions
- Topic: Test 2 Constants/Equations ERRORS
- Replies: 2
- Views: 266
Re: Test 2 Constants/Equations ERRORS
I also see mistakes on the formula sheet from my test 2. The first test and the midterm had correct formulas from what I can see from my test 1 that I have. I think it should be fixed for the final?? Hopefully??
- Sat Dec 07, 2019 1:34 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Knowing strong acids and bases
- Replies: 8
- Views: 524
Re: Knowing strong acids and bases
I believe it is helpful to memorize the seven strong acids which are (HBr, HCl, HI, HNO3, HClO4, HClO3, and H2SO4). For strong bases, they are Group 1 hydroxides, alkaline earth metal hydroxides (Ca(OH)2, Sr(OH)2, Ba(OH)2), and Group 1/Group 2 Oxides. This is all summarized in table J.1 of our textb...
- Sat Dec 07, 2019 1:28 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Equations
- Replies: 5
- Views: 149
Re: Equations
I believe that the formula sheet for the final should be the same as the other formula sheets provided for the previous exams. It does include the pH=-log[H+] formula, but does not have Ka on it from what I see.
- Sat Dec 07, 2019 1:26 pm
- Forum: Hybridization
- Topic: 2sp2 vs sp2
- Replies: 3
- Views: 1529
Re: 2sp2 vs sp2
The two is simply signifying the number of the row that the element is found. For example, you could apply this to other rows and put a 1 in front of the s when describing the hybridization of something including a Hydrogen (1s).
- Sun Dec 01, 2019 7:51 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Salt
- Replies: 5
- Views: 359
Re: Salt
If you are referring to salt, as in table salt, the molecular formula is NaCl. As such, it is an ionic compound that is soluble in water. Thus, it does not affect the pH of a solution, and therefore cannot impact how acidic or basic a solution is.
- Sun Dec 01, 2019 7:47 pm
- Forum: Lewis Structures
- Topic: Bent or Angular?
- Replies: 18
- Views: 1091
Re: Bent or Angular?
Bent and angular represent the same shape, so you should be able to use them interchangeably. I believe both are accepted on exams.
- Sun Dec 01, 2019 7:42 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH of Weak Acid and Bases
- Replies: 4
- Views: 330
Re: pH of Weak Acid and Bases
As you would with a strong acid/base, you must take the -log of the concentration of hydronium or hydroxide, but you must multiply the equilibrium constant (Ka) first, which is defined as
Ka= [A-][H+] / [AH]
Ka= [A-][H+] / [AH]
- Sun Dec 01, 2019 7:39 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Difference in Concentrations
- Replies: 3
- Views: 146
Re: Difference in Concentrations
The definition of an acid and base lies in the relative concentrations and characteristics associated with hydronium ion and hydroxide ions. Acids donate protons (H ions), while bases accept these (donate OH-). This can be seen in the basic formula for acid/base reaction: HA (parent acid) + B (paren...
- Sun Dec 01, 2019 7:34 pm
- Forum: Conjugate Acids & Bases
- Topic: Difference
- Replies: 2
- Views: 161
Re: Difference
A conjugate acid is what the parent base “turns into.” Consequently the conjugate base is what the parent acid “turns into.” If you think about it, whatever contains a hydrogen is marked as an acid, as demonstrated in the basic formula given to us in lecture. HA (parent acid) + B (parent base) -> A-...
- Sun Nov 24, 2019 12:14 pm
- Forum: Hybridization
- Topic: Strength of sigma and pi bonds
- Replies: 8
- Views: 657
Re: Strength of sigma and pi bonds
If you think about the various diagrams we were shown of the orbital hybridization, you can see that the sigma bonds’ orbitals overlap much more than the orbitals of the pi bonds as they directly overlay each other. This diagram I found helped me understand: https://qph.fs.quoracdn.net/main-qimg-a35...
- Sun Nov 24, 2019 12:03 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: AXE Format
- Replies: 34
- Views: 1107
Re: AXE Format
I don’t believe you have to write the subscript of one. If you think about the chemical formula of a molecule, like H2O, you only write the subscript on the element that has multiple atoms present (Hydrogen), while you do not write the 1 for the subscript on the oxygen. You can apply this thinking t...
- Fri Nov 22, 2019 6:26 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Lone pairs
- Replies: 13
- Views: 722
Re: Lone pairs
In the VSEPR theory that we use to name molecules, only the electrons associated with the central atom are considered. If you look at the VSEPR formula, which involved A-the central atom, X-number of bonds connected to the central atom, and E- number of lone pairs/a radical on the central atom. Thus...
- Fri Nov 22, 2019 6:11 pm
- Forum: Bond Lengths & Energies
- Topic: Boiling Point vs Melting Point
- Replies: 5
- Views: 619
Re: Boiling Point vs Melting Point
Boiling point and melting point can both act as indicators of the relative strength of intermolecular forces and are closely related. The difference between the two lies in the phase or state of the compound. Thus, a boiling point is the temperature that a liquid turns to gas, and a melting point is...
- Fri Nov 22, 2019 6:05 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Polarity and melting and boiling points
- Replies: 3
- Views: 498
Re: Polarity and melting and boiling points
There isn’t a direct relationship between polarity and melting point or boiling point. The factor that influences the relative height of such points is the strength of intermolecular forces. These intermolecular forces can be ion-ion, ion-dipole, hydrogen bond, dipole-dipole, etc. Dipoles are create...
- Sun Nov 17, 2019 12:28 am
- Forum: Electronegativity
- Topic: Symbols for partial charge
- Replies: 4
- Views: 4387
Re: Symbols for partial charge
The various delta symbols do in fact show a partial charge. If you think about a water molecule, the two hydrogens will have a delta positive and the oxygen will have a delta negative. The arrows point towards the negative atom. So the point of the arrow will go towards the oxygen in the case of wat...
- Sun Nov 17, 2019 12:01 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 5
- Views: 365
Re: Bond Angles
For each of the different molecular geometry shapes (VSEPR), I am memorizing the possible angles. Otherwise, I believe that is important to understand why an angle might be slightly less than expected (such as 107deg instead of expected 109.5deg) by understanding the role that lone pairs play in rep...
- Sat Nov 16, 2019 11:55 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Electronegativity
- Replies: 5
- Views: 293
Re: Electronegativity
I do not believe we need to know exact values for electronegativity. I think that knowing the general periodic trends associated with it are sufficient in that noble gases are not electronegative and electronegativity increases up a column and across a row. Comparing relative electronegativity can b...
- Sat Nov 16, 2019 11:42 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Calculating formal charge
- Replies: 8
- Views: 629
Re: Calculating formal charge
When calculating formal charge, the order that you do it in should not matter. Formal charge is assigned individually to each atom in a molecule by taking the number of valence electrons and subtracting the sum of the number of bonds and the number of lone electrons. Overall, you want the most elect...
- Sat Nov 16, 2019 11:33 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 4
- Views: 302
Re: Bond Angles
What I noted is that you should be able to tell when the bond angles are less than the expected (i.e. less than 109.5 deg in the example you give), but it is also helpful to be able to rank them when comparing various shapes, such as the bond angles on a molecule with one lone pair against a molecul...
- Sun Nov 10, 2019 3:13 pm
- Forum: Bond Lengths & Energies
- Topic: Bond Strength
- Replies: 4
- Views: 251
Re: Bond Strength
I believe that exact values of bond strength are determined experimentally through finding the dissociation energy. For our purposes, we can use a provided table of bond strengths and lengths to determine strength. The more bonds there are between atoms, the stronger the bond. Additionally, the shor...
- Sun Nov 10, 2019 3:07 pm
- Forum: Coordinate Covalent Bonds
- Topic: Coordinate Covalent Bond
- Replies: 8
- Views: 594
Re: Coordinate Covalent Bond
A coordinate covalent bond is special because both electrons in the shared lone pair came from the same atom. In a regular covalent bond, each atom in the bond provide an electron. I believe that the strength of a coordinate covalent bond is equivalent to any other covalent bond and its importance i...
- Sun Nov 10, 2019 2:58 pm
- Forum: Lewis Structures
- Topic: Lewis acids and bases?
- Replies: 7
- Views: 388
Re: Lewis acids and bases?
I would think that we are held responsible for understanding Lewis acids and bases for all of the upcoming assessments. It appears on the syllabus in Focus 3: Chemical bonds. We did not complete all of focus 3 before the midterm, but I assume that the material will be fair game on future tests. I re...
- Sun Nov 10, 2019 2:51 pm
- Forum: Ionic & Covalent Bonds
- Topic: C, N, O, and F
- Replies: 13
- Views: 609
Re: C, N, O, and F
As Carbon, Nitrogen, Oxygen, and Fluorine are all located in period 2 of the periodic table, their valence electrons are found in n=2. Thus, they do not have the extra 3d subshell that would allow them to have an expanded octet an must follow the octet guideline. Furthermore, although we try to mini...
- Sun Nov 10, 2019 2:47 pm
- Forum: Ionic & Covalent Bonds
- Topic: covalent relationship to polarizability
- Replies: 4
- Views: 145
Re: covalent relationship to polarizability
When atoms are highly polarizable or have high polarizing power, they are able to pull the electrons between them closer to the cation. An ionic bond is formed by the attraction between two oppositely charged atoms. As a covalent bond is defined by a sharing of electrons between the two bonded atoms...
- Sat Nov 02, 2019 11:31 pm
- Forum: Electronegativity
- Topic: What is isoelectronic?
- Replies: 13
- Views: 760
Re: What is isoelectronic?
Isoelectronic simply means that the atoms being compared have the same number of electrons. This is often demonstrated by ions, like S- being isoelectronic with Cl.
- Sat Nov 02, 2019 11:24 pm
- Forum: Octet Exceptions
- Topic: Covalent Bond
- Replies: 4
- Views: 217
Re: Covalent Bond
Coordinate covalent bonds appear as normal covalent bonds with two electrons shared between two atoms. What makes coordinate bonds special is that the two electrons that are shared both came from one atom, rather than each atom contributing one electron.
- Sat Nov 02, 2019 11:19 pm
- Forum: Lewis Structures
- Topic: Expanded Octet
- Replies: 3
- Views: 121
Re: Expanded Octet
Atoms with an open d or f orbital can have an expanded octet. Thus, atoms in the n=3 level or greater can have this occur. As for determining if an atom as an expanded octet, it is important to assess its formal charge and adjust the structure accordingly to get the formal charge of all atoms as clo...
- Sat Nov 02, 2019 11:11 pm
- Forum: Lewis Structures
- Topic: Dino Nugs 12b
- Replies: 5
- Views: 277
Re: Dino Nugs 12b
You want the most electronegative atom to take the negative formal charge. In this case, it is Oxygen and you would want the -1 formal charge to be assigned to it.
- Sat Nov 02, 2019 11:04 pm
- Forum: Ionic & Covalent Bonds
- Topic: ionic vs. covalent
- Replies: 7
- Views: 357
Re: ionic vs. covalent
Solely based off of the visual representation of a Lewis Structure, a covalent bond is represented with a line between two atoms, as they are sharing electrons. In an ionic bond, the atoms are not sharing electrons and are not represented with a line between them.
- Sun Oct 27, 2019 8:04 pm
- Forum: Trends in The Periodic Table
- Topic: Ionization energy
- Replies: 12
- Views: 584
Re: Ionization energy
I believe that it is most important to understand the general trends associated with ionization energy. Ionization energy is said to be the energy needed to remove an electron from an atom in the gas phase. Thus, ionization energy decreases down a group and increases across a period.
- Sun Oct 27, 2019 8:01 pm
- Forum: Trends in The Periodic Table
- Topic: Central Atom
- Replies: 13
- Views: 487
Re: Central Atom
Typically the atom with the lowest electronegativity is the central atom. The only exception to the rule is Hydrogen.
- Sun Oct 27, 2019 7:57 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron configurations
- Replies: 3
- Views: 176
Re: Electron configurations
The only time to expand into the descriptive x, y, and z is when it is specified in the question or asked for. Otherwise, I believe it is fine to leave the configuration in its simplified form (no x, y, z). The x, y, and z are not necessarily part of the 4 main quantum numbers.
- Sun Oct 27, 2019 7:54 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: p-orbitals
- Replies: 11
- Views: 396
Re: p-orbitals
I believe that you can leave it as the more simplified version. If you look in the periodic table in the textbook, they list electron configurations for various elements and all of them are left in the simplified form (not displaying the x,y,z)
- Sun Oct 27, 2019 7:51 pm
- Forum: Ionic & Covalent Bonds
- Topic: Resonance
- Replies: 10
- Views: 389
Re: Resonance
Having resonance does not necessarily mean that there are exactly three ways to draw the Lewis structure. Rather, resonance means that the molecule being examined has more a more complex bonding structure. A Lewis structure is a simplification of what a molecule really is, as demonstrated by the dif...
- Sun Oct 20, 2019 11:28 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Multi-electron atoms
- Replies: 7
- Views: 282
Re: Multi-electron atoms
Hydrogen is the only element that has one electron in its ground state. Otherwise, all other elements can be considered multi-electron atoms. Helium could hypothetically be stripped of an electron (even though highly unlikely/extremely difficult because it is highly stable) and become a single-elect...
- Sun Oct 20, 2019 11:20 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg
- Replies: 5
- Views: 235
Re: Heisenberg
To address Quresh’s question: Momentum is found by multiplying mass times velocity (p=mv). It describes the amount of resistance to stopping that an object in motion has. If you think about two balls rolling at the same velocity but with different weights, the heavier one has more momentum and is th...
- Sun Oct 20, 2019 11:12 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Exceptions to Orbital Rules
- Replies: 8
- Views: 1384
Re: Exceptions to Orbital Rules
The exceptions to the expected electron configurations come with Chromium and Copper. Chromium’s electron configuration is [Ar] 3d^5 4s^1. Copper’s is [Ar] 3d^10 4s^1. As for what half filled and full subshells mean, a d subshell can have up to 10 electrons in it, and half-full would be 5 electrons ...
- Sun Oct 20, 2019 11:06 pm
- Forum: Properties of Electrons
- Topic: What's the difference between a shell, a subshell, an energy level, and an orbital?
- Replies: 8
- Views: 571
Re: What's the difference between a shell, a subshell, an energy level, and an orbital?
A shell is defined by n, which can be whole number values (1, 2, 3, etc). The term subshell refers to the l (s, p, d, f) and the shapes that are made by the expected/potential location of the electron. An orbital is a combination/description of all of the quantum numbers (which are n, l, ml, and ms)...
- Sun Oct 20, 2019 10:52 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: What is electron configuration?
- Replies: 3
- Views: 172
Re: What is electron configuration?
An electron configuration is the symbolic representation of where an electron is located within an atom. Each of the levels within electron configuration denotes a certain amount of energy that an electron possesses. An element can be defined by its electron configuration because its is marked by it...
- Sun Oct 13, 2019 10:15 pm
- Forum: Properties of Light
- Topic: De Broglie equation
- Replies: 4
- Views: 131
Re: De Broglie equation
De Broglie's equation is used to find the wavelength.
The equation itself is:
Wavelength = Planck's constant / (mass X velocity)
The units of planck's constant (m^2kg/s) cancel down to meters, as it is divided by mass (kg) and velocity (m/s) respectively.
The equation itself is:
Wavelength = Planck's constant / (mass X velocity)
The units of planck's constant (m^2kg/s) cancel down to meters, as it is divided by mass (kg) and velocity (m/s) respectively.
- Sun Oct 13, 2019 10:04 pm
- Forum: DeBroglie Equation
- Topic: Detectable wavelike properties
- Replies: 1
- Views: 70
Re: Detectable wavelike properties
In lecture, Dr. Lavelle said that a particle with less than 10^-15m does not have detectable wavelike properties. So anything larger than that should qualify.
- Sun Oct 13, 2019 9:48 pm
- Forum: Properties of Light
- Topic: Reading entire chapters before class?
- Replies: 4
- Views: 194
Re: Reading entire chapters before class?
I tend to do most of the reading listed on the syllabus above the problem set before I attempt to do any problems. I only read what he has listed online. For example, he omitted section 1C for the Quantum World. I don't take notes on everything, only main formulas or things that are essential or thi...
- Sun Oct 13, 2019 9:31 pm
- Forum: Photoelectric Effect
- Topic: Photoelectric Effect
- Replies: 3
- Views: 202
Re: Photoelectric Effect
Light has both wave-like and particle-like tendencies. The particle-like behavior is reflected in photons, which I think of as a small package of energy.
- Sun Oct 13, 2019 9:27 pm
- Forum: Properties of Electrons
- Topic: Decrease in Quantum level
- Replies: 3
- Views: 98
Re: Decrease in Quantum level
If you think of the concept that energy is neither created or destroyed, the release of the light reflects a decrease in energy for the atom as a whole. The further the gap between the starting and final energy levels does impact the frequency of the light emitted, thus allowing us to analyze the va...
- Fri Oct 04, 2019 10:35 pm
- Forum: Balancing Chemical Reactions
- Topic: Understanding how to get whole #s [ENDORSED]
- Replies: 18
- Views: 1199
Re: Understanding how to get whole #s [ENDORSED]
If you are simply converting from grams to moles, or vice versa, having decimals is acceptable, as long as they go along with the rules of significant figures. In the case of 2.44, you have three significant figures listed. If you are making an empirical formula, you should not have decimals for the...
- Fri Oct 04, 2019 10:26 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Clarification
- Replies: 7
- Views: 447
Re: Clarification
The moles of solute remain the same, regardless of the dilution. There is a set number of molecules of the solute in a solution. Even if more solvent is added, the number of molecules of solute will not change, as there is no solute being added or removed. There is simply more solvent being added, w...
- Fri Oct 04, 2019 10:20 pm
- Forum: Properties of Light
- Topic: Amplitude
- Replies: 6
- Views: 386
Re: Amplitude
Wavelength and frequency are inversely related, as when they are multiplied, they result in a constant. I believe that amplitude is a separate value with no relation to the other two. For example, a wave might have a set frequency, and thus a set wavelength to compensate. The amplitude could be any ...
- Fri Oct 04, 2019 10:07 pm
- Forum: Empirical & Molecular Formulas
- Topic: Difference between empirical and molecular formulas
- Replies: 6
- Views: 2047
Re: Difference between empirical and molecular formulas
The empirical formula shows only the ratio/proportions of atoms of the elements present in a molecule. Conversely, the molecular formula shows the exact number of atoms of each element that are present in a molecule. The way that I remember the difference is the when you want to look at a specific m...
- Fri Oct 04, 2019 9:56 pm
- Forum: Student Social/Study Group
- Topic: Final Jitters
- Replies: 457
- Views: 336742
Re: Final Jitters
As many of us do, I also struggle with stress/jitters before a large exam. Some of the strategies to cope with it that I have found useful are: 1. Take a break from the material and do something active. I personally like going to the gym or running. It helps me get my mind off of the problems at han...