## Search found 50 matches

Thu Mar 15, 2018 11:12 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Negative Ea
Replies: 3
Views: 237

### Re: Negative Ea

Activation energy cannot be negative because it is the minimum amount of energy that a reaction requires to undergo a specific reaction, making it positive. So if the activation energy were to be negative, then that would mean there is a release of energy.
Thu Mar 15, 2018 11:09 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: delta U
Replies: 2
Views: 291

### Re: delta U

In isothermal processes, ΔU will be 0.
Thu Mar 15, 2018 11:07 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Temperature for an ideal gas
Replies: 2
Views: 265

### Re: Temperature for an ideal gas

I think changing the temperature does cause a change in pressure/volume. Because for a gas, for example, when heated, the particles move more rapidly and this causes them to expand ?
Sat Mar 10, 2018 9:09 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.25
Replies: 1
Views: 290

### Re: 8.25

The problem is asking you to calculate ΔU, the change in the internal energy. It is given that it is a constant-volume calorimeter, so you know that there is no ΔV therefore, w=0. That being said, we know that ΔU=q. Use the equation -q cal =CΔT to solve for C---you should get the value -478.1 J. We ...
Sat Mar 10, 2018 8:58 am
Forum: Experimental Details
Topic: Experimental Techniques
Replies: 3
Views: 581

### Re: Experimental Techniques

To measure the rate of a reaction, you can use the differential rate law which is k[Reactancts] n with n being the amount of moles; the differential rate law is rate as a function of concentration of reactants. On the other hand, you can also use the integrated rate law which is [A] t = -kt + [A] 0 ...
Sat Mar 10, 2018 8:49 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.53
Replies: 3
Views: 332

### Re: 8.53

You use the value of 1.40 g CO because you know the change in temperature caused by this amount of CO, and so you can then set a ratio to get the change in temperature for one mole of CO (28 g CO). That being said, you could take 1.40 g CO/.686°C = 28.0 g CO/ΔT and cross-multiply to solve for ΔT to ...
Sat Mar 03, 2018 10:16 pm
Forum: Second Order Reactions
Topic: Half Lives [ENDORSED]
Replies: 3
Views: 225

### Re: Half Lives[ENDORSED]

Half lives depend on the initial concentration of A. If the initial concentration of A is larger, it will take a longer time for half of it to decay than if the initial concentration was smaller.
Sat Mar 03, 2018 10:07 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q vs. K
Replies: 8
Views: 575

### Re: Q vs. K

Q is the the reaction quotient and K is the equilibrium constant. Both Q and K are calculated the same way (by using pressures or concentrations) but they are applied differently depending on the equation that you are using. Because they are calculated the same, it shouldn't make too much of a diffe...
Sat Mar 03, 2018 9:58 pm
Forum: General Rate Laws
Topic: half-life
Replies: 8
Views: 412

### Re: half-life

Also, going off of finding the half-life, remember that you can also find the "one-third" life or "one-fourth" life, etc.
Sun Feb 25, 2018 7:13 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Dissolving metal in a solution
Replies: 3
Views: 228

### Re: Dissolving metal in a solution

Given the metal and the solution that you are observing, you form a balanced chemical equation using the half-reactions and their E° values. Once you calculate the E° value for the balance chemical equation, you get a value that is either positive or negative. If E° is negative, then ΔG is positive,...
Sun Feb 25, 2018 7:05 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Reducing Agent/ Oxidizing Agent
Replies: 6
Views: 618

### Re: Reducing Agent/ Oxidizing Agent

E° = standard reduction potential
When comparing the values of E°, you can use the rules:
- most easily reduced element/best oxidizing agent = higher E°
- most easily oxidized element/best reducing agent = lower E°
Sun Feb 25, 2018 6:56 pm
Forum: General Rate Laws
Topic: Rate law equations
Replies: 3
Views: 259

### Re: Rate law equations

The two equations are equal to each other; therefore, you can use either one. The equation k[R]^n is just the other reaction rate equation reexpressed after doing experiments to observe d[R]/dt. The equation k[R]^n is in terms of the rate constant, k, the concentration of reactant, [R], and the orde...
Wed Feb 14, 2018 2:10 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: Standard molar entropy vs. residual entropy
Replies: 2
Views: 319

### Re: Standard molar entropy vs. residual entropy

Residual entropy is the measure of how many different arrangements a molecule can have. Molar entropy is a measure of a molecule's chaos. Both of your statements above are true, and they don't oppose one another. You can compare two molecules, and have one molecule have higher residual entropy AND a...
Wed Feb 14, 2018 1:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What does E stand for?
Replies: 3
Views: 313

### Re: What does E stand for?

E is referring to the cell potential. (We are currently learning about this in electrochemistry.)
Wed Feb 14, 2018 1:18 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: homework 8.67
Replies: 3
Views: 262

### Re: homework 8.67

How did you know that the amount of heat released when H2O goes from a gas to a liquid was -44 kj/mol?
Sat Feb 10, 2018 2:48 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Question related to previous midterm
Replies: 1
Views: 188

### Re: Question related to previous midterm

Yes, hydrogen atoms barely have any mass compared to fluorine atoms. Therefore, since the molecules being compared are made up of only carbon, fluorine, and hydrogen, the molecules with the a higher ratio of fluorine to hydrogen would have the greater molar entropies.
Sat Feb 10, 2018 2:43 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.81? Why is Fe2O3 more thermodynamically stable than Fe3O4?
Replies: 1
Views: 296

### Re: 9.81? Why is Fe2O3 more thermodynamically stable than Fe3O4?

If a reaction has a higher chance of occurring more spontaneously, then it would be considered less stable because less stable particles are more likely to react.
Sat Feb 10, 2018 2:40 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equilibrium Constant when calculating gibbs free energy
Replies: 1
Views: 135

### Re: Equilibrium Constant when calculating gibbs free energy

I'm pretty sure it can be calculated using either pressures or concentrations, but I'm not 100% sure. I know that Q can be calculated using both pressures and concentrations, though. So I think the same applies to K.
Sat Feb 03, 2018 5:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Value of G
Replies: 4
Views: 206

### Re: Value of G

Yes, I'm not sure if G can have a lowest value, but if I'm remembering correctly, Lavelle said that measuring G alone is very difficult, therefore we always measure the change in G. If you meant to ask about DeltaG, DeltaG can't have a lowest value, and if it does, then it definitely wouldn't be 0! ...
Sat Feb 03, 2018 5:54 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: ΔS(universe)
Replies: 6
Views: 350

### Re: ΔS(universe)

This is a really helpful explanation! The analogy that Lavelle really helps to provide an example as to why the Second Law of Thermodynamics proves to be true. Compared to the universe, the entropy observed in a system will always be too small to have any notable effect on the universe's entropy, an...
Sat Feb 03, 2018 4:13 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Difference between deltaS(tot), deltaS and deltaS(surr)
Replies: 5
Views: 398

### Re: Difference between deltaS(tot), deltaS and deltaS(surr)

Yes, I agree with what is said above! DeltaS of the system added to the DeltaS of the surroundings are equal to the DeltaS total/universe. Some other points to remember are that if the calculated DeltaS total value is greater than 0, then the reaction being observed is spontaneous, and oppositely, i...
Sun Jan 28, 2018 4:46 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: degeneracy
Replies: 3
Views: 193

### Re: degeneracy

I know Prof. Lavelle stated that degeneracy is the number of ways of achieving a given energy state, and then connects it to the entropy through the Boltzman Equation which is S = klnW. So is that how we find it? If we use entropy to find degeneracy?
Sun Jan 28, 2018 4:40 pm
Forum: Calculating Work of Expansion
Topic: Diagram of Reversible Expansion
Replies: 3
Views: 247

### Re: Diagram of Reversible Expansion

A vacuum is a volume that encloses little or no matter. In other words, it is a region that has a gaseous pressure much lower than that of atmospheric pressure---so that's what it represents in the system with the ideal gas that we were shown in class!
Sun Jan 28, 2018 4:34 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Week 3 Friday Lecture
Replies: 2
Views: 149

### Re: Week 3 Friday Lecture

He said, "The magnitude of deltaS depends on temperature at which heat is transferred. Therefore, deltaH [or q] plays an important/bigger role at a lower temperature." (:
Sat Jan 20, 2018 6:54 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.5 specific heat capacity vs molar heat capacity?
Replies: 1
Views: 157

### Re: 8.5 specific heat capacity vs molar heat capacity?

I believe that they are equal, but q=CdeltaT is the general form of the equation, assuming that you are only reacting 1 gram or 1 mole of something. If the amount of whatever you are reacting is not 1, then the calculations need to be specific to the amount of whatever you are reacting. Therefore, i...
Mon Jan 15, 2018 5:18 pm
Forum: Phase Changes & Related Calculations
Topic: Exercise 8.31
Replies: 3
Views: 202

### Re: Exercise 8.31

It's a given! It's explained in Chapter 8.10 of the textbook! (:
Mon Jan 15, 2018 12:34 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Example 8.3
Replies: 2
Views: 147

### Example 8.3

Example 8.3a) Calculate the heat necessary to increase the temperature of 100. g of water from 20 degrees Celsius to 100 degrees Celsius. In the worked out calculation, the delta T value used is 80. K. Why is the temperature change 80 K instead of 353.1 K? It seems that they just changed the units w...
Fri Jan 12, 2018 12:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of Formation vs Standard Enthalpy of Reaction
Replies: 3
Views: 172

### Re: Standard Enthalpy of Formation vs Standard Enthalpy of Reaction

By definition according to Lavelle, standard enthalpy of a reaction occurs when all reactants and products are in their standard states at 1 ATM. It's also known as reaction enthalpy. Standard enthalpy of formation, on the other hand, is the standard reaction enthalpy for the formation of one mole o...
Fri Jan 12, 2018 12:49 pm
Forum: Administrative Questions and Class Announcements
Topic: Times to post per week
Replies: 5
Views: 392

### Re: Times to post per week

Correct! The cutoff time for each week is Sunday at 11:59pm.
Fri Jan 12, 2018 12:48 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and work not state functions
Replies: 7
Views: 519

### Re: Heat and work not state functions

Heat and work are not state functions. Work can't be a state function because it is proportional to the distance an object is moved, which depends on the path used to go from the initial to the final state. Same with heat. I hope this is helpful!
Sat Dec 09, 2017 11:14 pm
Forum: Trends in The Periodic Table
Topic: Isoelectronic Ionic Radius
Replies: 2
Views: 228

### Re: Isoelectronic Ionic Radius

Each element has the same amount of electrons, but the amount of protons is not changing. Therefore, the elements with more protons have a stronger pull on the electrons making the atomic radius decrease.
Sat Dec 09, 2017 11:09 pm
Forum: Photoelectric Effect
Topic: Test 2, #7a
Replies: 2
Views: 279

### Test 2, #7a

Hi guys! Can someone please guide me through the steps of solving this problem. When asked for help during the review session, it was said that there was an issue with the kinetic energy relative to the energy of the photon. Here's the question: An electron was ejected from the surface of an unknown...
Sun Dec 03, 2017 5:07 pm
Forum: Dipole Moments
Topic: Dipole Moments and Polarity
Replies: 9
Views: 535

### Re: Dipole Moments and Polarity

How do you calculate the electronegativity for the atoms of a specific element?
Sun Dec 03, 2017 4:53 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Notes on 11.37
Replies: 3
Views: 391

### Re: Notes on 11.37

Are there other rules/tips/tricks that are useful for manipulating equilibrium constants?
Tue Nov 28, 2017 6:46 am
Forum: Naming
Topic: Problem 17.29
Replies: 1
Views: 160

### Problem 17.29

Can someone please explain to me why the answer to b) ends with cobalt compared to the answer to c) which ends in cobaltate? I need clarification on when to add the -ate at the end of the metal name.
Mon Nov 27, 2017 12:09 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8017
Views: 1402863

### Re: Post All Chemistry Jokes Here

Did you know that you can cool yourself to -273.15˚C and still be 0k?
Mon Nov 27, 2017 12:05 am
Forum: Biological Examples
Topic: Memorization of compounds
Replies: 5
Views: 533

### Re: Memorization of compounds

I’d memorize them. The more tools you have in your toolbox, the better.
Sun Nov 19, 2017 10:45 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: MOT
Replies: 2
Views: 226

### Re: MOT

Yea, we will be covering it. I believe it's in Chapter 4 if I'm not mistaking.
Sun Nov 19, 2017 10:38 pm
Forum: Lewis Structures
Topic: Best way to start Lewis Structures
Replies: 12
Views: 727

### Re: Best way to start Lewis Structures

I usually like to draw one bond between each of the atoms and then I assign the rest of the valence electrons!
Sun Nov 12, 2017 9:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.1
Replies: 5
Views: 287

### Re: 4.1

Bond angle determines if a molecule has lone pairs because lone pairs have strong repulsive factors that cause it to displace the other atoms, pushing other atoms closer together. This causes the bond angle between the other two atoms to decrease. Therefore, if there is a lone pair for part B, the s...
Sun Nov 12, 2017 9:21 pm
Forum: Octet Exceptions
Topic: Expanded Octet
Replies: 4
Views: 376

### Re: Expanded Octet

All elements in period 3 and further have the ability to have more than 8 valence electrons.
Sun Nov 05, 2017 11:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shell, subshell, and orbital
Replies: 5
Views: 444

### Re: Shell, subshell, and orbital

The minimum numbers for n and l are 0, but the minimum number for ml would depend on the value of l which can range from 0 all the way to infinity, theoretically. But if applying what we know about energy levels, as energy level n gets larger, the electrons in these energy levels become virtually un...
Sun Nov 05, 2017 10:59 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals of subshell
Replies: 3
Views: 203

### Re: Orbitals of subshell

The magnetic quantum number ml determines the number of orbitals and their orientation within a subshell. Its value depends on the orbital angular momentum quantum number l. Given a certain value for l, ml is an interval ranging from the negative value of l to the positive value of l, so it can be z...
Sun Nov 05, 2017 10:49 pm
Forum: SI Units, Unit Conversions
Topic: Si Unit for molar mass
Replies: 3
Views: 1162

### Re: Si Unit for molar mass

I agree with the post above. It's important to always keep the units consistent with the form of the unit in the final answer.
Thu Oct 26, 2017 6:31 pm
Forum: Lewis Structures
Topic: S and P blocks and Lewis structures [ENDORSED]
Replies: 4
Views: 406

### Re: S and P blocks and Lewis structures[ENDORSED]

The octet rule can be used for the some of the s- and p- block elements (with exception for the lighter elements in these blocks), and only applies to some of the elements in the d- block. General exceptions to the octet rule: (1) molecules whose atoms have fewer than 8 electrons (e.g., boron chlori...
Thu Oct 26, 2017 6:16 pm
Forum: Hybridization
Topic: Filling electron shells [ENDORSED]
Replies: 3
Views: 366

### Filling electron shells[ENDORSED]

Why do certain orbitals get filled first even though the other orbitals have a smaller number? (for example, 4s fills before 3d)
Mon Oct 16, 2017 9:44 pm
Forum: Photoelectric Effect
Topic: Sodium Vapor Lamps (1.19 hw) [ENDORSED]
Replies: 6
Views: 9843

### Re: Sodium Vapor Lamps (1.19 hw)[ENDORSED]

Why is it that we use E = h(c/λ) instead of just E = hv?
Mon Oct 16, 2017 5:38 pm
Forum: Properties of Light
Topic: Rydberg's Constant
Replies: 4
Views: 514

### Rydberg's Constant

I am having trouble on Question 1.13 on the homework and I'm thinking that it might be because I have Rydberg's formula or constant wrong. On Lavelle's Atomic Spectra video module it says that the Rydberg's constant is R = 3.29 x 10^15 s^-1, but online it is saying that R = 1.09 x 10^7 m^-1. Which o...
Fri Oct 13, 2017 10:26 am
Forum: Properties of Light
Topic: Converting Units [ENDORSED]
Replies: 11
Views: 764

### Re: Converting Units[ENDORSED]

^ I agree with both people. Lavelle said in lecture that it's okay to leave it in meters, but as stated above, it'll be easier to interpret and use the calculation if it were to be converted.
Sun Oct 08, 2017 11:47 pm
Forum: Administrative Questions and Class Announcements
Topic: Chapter 1 Test this week [ENDORSED]
Replies: 2
Views: 233

### Re: Chapter 1 Test this week[ENDORSED]

The next test isn't until next week (:

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