## Search found 35 matches

Fri Mar 15, 2019 12:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test #1
Replies: 3
Views: 330

### Re: Test #1

[H2] = 0.066 mol/L
[Cl2] = 1.066 mol/L
[HCl] = 1.868 mol/L
[HCl] = 0.934 mol/L
Thu Mar 14, 2019 11:43 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibrium approach
Replies: 3
Views: 123

### Re: Pre-Equilibrium approach

Yes, the first elementary step has to be a fast reaction so it can have a bottleneck effect to where you plug in its equilibrium into your rate for the slow so it can match the proposed reaction rate.
Thu Mar 14, 2019 11:37 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 2
Views: 255

### Re: Nernst Equation

The first equation is written is for any E reaction value at any temperature. The second one is specific to room temperature (25 degrees Celcius).
Mon Mar 04, 2019 4:40 pm
Forum: General Rate Laws
Topic: units of rates and rate constants
Replies: 4
Views: 189

### Re: units of rates and rate constants

for 0 order reaction, k = mol/Ls. For 1st order, k = 1/s. For 2nd order, k = L/(mol s). Overall the units for a reaction should be mol/Ls
Mon Mar 04, 2019 4:38 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation (log vs. ln)
Replies: 5
Views: 2135

### Re: Nernst Equation (log vs. ln)

Dhwani Krishnan 1G wrote:do both yield the same results?

Yes if you make sure ln x= 2.303 log x. Otherwise your answers would both be the same
Mon Mar 04, 2019 4:36 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7A. 1 in the 7th edition
Replies: 4
Views: 137

### Re: 7A. 1 in the 7th edition

it's similar to what Lavelle went over on Friday in lecture to where you treat it like a ratio
Mon Mar 04, 2019 4:30 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst
Replies: 6
Views: 181

### Re: Nernst

it's more common to use log especially when dealing with pH, but otherwise they can be used interchangeably when ln x = 2.303 log x
Wed Feb 20, 2019 12:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 3
Replies: 10
Views: 352

### Re: Test 3

Emily Kennedy 4L wrote:how much of electrochemistry do you think it will include?

Whatever we learned today and learn on Friday, I'm assuming.
The test only covers material from week 6 and 7
Wed Feb 20, 2019 12:19 pm
Forum: Balancing Redox Reactions
Topic: Trends
Replies: 5
Views: 144

### Re: Trends

There are trends for oxidization states. I expect he will tell us them later but some are:
H is usually +1 unless attached to a less electronegative element then it becomes -1
oxidization of a free element is always 0
oxygen is usually -2 unless in peroxide O2 then its -1
Wed Feb 20, 2019 10:49 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: O2
Replies: 5
Views: 182

### Re: O2

O2 is naturally occurring so its O. This is the same for H2 and N2
Wed Feb 20, 2019 10:48 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G a state function?
Replies: 23
Views: 824

### Re: Delta G a state function?

Aidan Ryan 1B wrote:What are things we have learned that are not state functions?

along with work, heat is also not a state function
Wed Feb 20, 2019 10:47 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reverse Reaction
Replies: 8
Views: 257

### Re: Reverse Reaction

if you mean in terms of K then the reverse reaction would be 1/{K} from the K of the forward reaction. If you mean when solving enthalpy, its H times -1
Wed Feb 20, 2019 10:45 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta Srxn
Replies: 4
Views: 563

### Re: Delta Srxn

the m stands for molar or mass depending on what you are given and what you need to find. If you need to find over kJ/mol and you were given mass you would need to convert to moles. The reason why there is an m is mostly because S is extensive.
Wed Feb 20, 2019 10:44 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ignoring x validity
Replies: 6
Views: 456

### Re: ignoring x validity

you only ignore the x generally when x<10^-3. Usually, x will be less than 5%, but if it isn't then you would do quadratic as your answer would be slightly off otherwise.
Wed Feb 20, 2019 10:41 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units of Gibbs Free Energy
Replies: 5
Views: 209

### Re: Units of Gibbs Free Energy

Gibbs free energy is extensive because it depends on the amount like entropy and enthlapy
Tue Feb 12, 2019 1:52 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Acid Base
Replies: 3
Views: 364

### Re: Acid Base

It is correct to take the pKa value and raise it to 10 ^-pKa to get Ka which you can then use for x to solve for [H+] and then take the -log of to get the pH. pKa and pH correlate to the Ka value but are not equal. Ka refers to how much of acid actually dissociates and pKa gives you the acidity of i...
Mon Feb 11, 2019 4:06 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Study Guides
Replies: 15
Views: 515

### Re: Study Guides

I know Sonia said she would post the sheet she made with questions that are similar to what questions are going to be on the midterm from today's review session, but I don't know when she's going to post it. Where on Chemistry Community can this worksheet be found? https://lavelle.chem.ucla.edu/for...
Sun Feb 10, 2019 9:38 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 8
Views: 278

### Re: Delta U

delta u is zero when there is no temperature change
Thu Feb 07, 2019 8:19 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Study Guides
Replies: 15
Views: 515

### Re: Study Guides

MMoreno3K wrote:
ariana_apopei1K wrote:Lyndon is probably going to make one that he'll go over in his review session this monday

Do you know where and what time his review session will be?

I believe it's from 7-10 pm at Franz Hall 1178
Thu Feb 07, 2019 8:18 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Study Guides
Replies: 15
Views: 515

### Re: Study Guides

I know Sonia said she would post the sheet she made with questions that are similar to what questions are going to be on the midterm from today's review session, but I don't know when she's going to post it.
Sun Feb 03, 2019 7:17 pm
Forum: Phase Changes & Related Calculations
Topic: Water vapor vs boiling water burns
Replies: 3
Views: 169

### Re: Water vapor vs boiling water burns

This can be seen on the phase change chart during lecture. So boiling water heats up to a high temperature but it is still in liquid phase. The water vapor has to go through a phase change to turn into a gas gaining more energy/temperature into causing it to burn more than boiling water
Sun Feb 03, 2019 7:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: HW
Replies: 3
Views: 129

### Re: HW

you can start thermochemistry if you want too but we are currently still on thermodynamics. I think you will be alright if you turn in homework from thermochemistry though.
Sun Feb 03, 2019 7:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: finding W
Replies: 6
Views: 218

### Re: finding W

the two equations mean the same thing just written in different ways
Sun Feb 03, 2019 7:12 pm
Forum: Phase Changes & Related Calculations
Topic: Work
Replies: 2
Views: 118

### Re: Work

work is a force being applied over a distance. W=fd
Sun Feb 03, 2019 7:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 7
Views: 296

### Re: Delta U

a positive delta u means in an increase in the internal energy due to an increase in temperature
a negative delta u means in a decrease in the internal energy due to a decrease in temperature
Sat Feb 02, 2019 12:00 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: pressure
Replies: 3
Views: 180

### Re: pressure

You usually the pressure of a system is at 1 atm when you aren't given any pressure in the question
Wed Jan 23, 2019 10:31 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acidity & Basicity Constants
Replies: 3
Views: 97

### Re: Acidity & Basicity Constants

Dr. Lavelle will provide us with a sheet with all the constants you need for every test
Wed Jan 23, 2019 10:29 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: correct x from quadratic equation 12.55 6th edition
Replies: 1
Views: 42

### Re: correct x from quadratic equation 12.55 6th edition

if you are given two positive numbers you have to check which x value does not give you a negative concentration when you plug it back in to find the equilibrium concentrations because you can't have an negative concentration
Wed Jan 23, 2019 10:27 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5% Rule
Replies: 3
Views: 98

### Re: 5% Rule

if the Ka value is below 10^-3 then it is okay to assume that you can get rid of the -x when solving for x because you assume that the change is less than 5%. After solving for x though, just make sure to check that, in fact, it is less than 5% by using the equation x/(acid)initial * 100
Sun Jan 20, 2019 9:25 pm
Forum: Ideal Gases
Topic: pH and pOH
Replies: 18
Views: 868

### Re: pH and pOH

I don't know what the problem says but usually, it will tell you what to solve for in the problem. Given the reaction, you will know what you have to solve for. For instance if it NH3 + H20 -> NH4+ + OH- you would solve for Kb and pOH and if it was HCl + H20 -> Cl- + H30+.
Sun Jan 20, 2019 9:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc (Section 5H.3 7th Edition)
Replies: 2
Views: 81

### Re: K and Kc (Section 5H.3 7th Edition)

We don't need to know that equation but for if you do need to convert from Kc to Kp you would use P=MRT and from Kp to Kc M=P/RT
Wed Jan 16, 2019 9:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKw and Kw
Replies: 1
Views: 64

### Re: pKw and Kw

Kw refers to the concentration while pKw refers to the pH on a scale of 14. pKw comes in handy when you have the pH and you want to find the pOH or vice versa
Sat Jan 12, 2019 4:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solving for x in ICE table
Replies: 2
Views: 97

### Re: Solving for x in ICE table

you multiply (3.16*10^-3) with (0.114-x) getting 2x= (3.6*10^-4)-(3.16*10^-3)x. Then you get the x on one side getting 2.00316=3.6*10^-4
Wed Jan 09, 2019 4:11 pm
Forum: Ideal Gases
Topic: K values
Replies: 3
Views: 132

### Re: K values

The value between 10^-3 and 10^3 does represent a small change either to the left of the right; it's not a very strong change. These values are more important when we get to acids and bases to determine what's a weak or strong acid and base.
Wed Jan 09, 2019 3:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc
Replies: 8
Views: 237

### Re: K and Kc

Jordan Lo 2A wrote:Do we need to memorize the formula in the book for converting between the 2?

The only formula you need anyway to convert between the two is the ideal gas law, PV=nRT which changes to P=concentrationRT. It's handy to know, but I don't think you need to memorize it.