Search found 39 matches

by Maayan Epstein 14B
Sun Mar 17, 2019 10:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Exam Practice Problem
Replies: 3
Views: 43

Re: Final Exam Practice Problem

Thank you for these!
by Maayan Epstein 14B
Sun Mar 17, 2019 10:16 pm
Forum: Administrative Questions and Class Announcements
Topic: LYNDON'S PORK RAMEN REVIEW
Replies: 37
Views: 1463

Re: LYNDON'S PORK RAMEN REVIEW

Thank you for all your help this quarter, Lyndon!
by Maayan Epstein 14B
Sun Mar 17, 2019 10:15 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Week 9 Worksheet (2E,I,K)
Replies: 13
Views: 390

Re: Week 9 Worksheet (2E,I,K)

Thank you for all your help this quarter, Joyce!
by Maayan Epstein 14B
Sat Mar 16, 2019 10:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure Solids and Liquids
Replies: 4
Views: 42

Re: Pure Solids and Liquids

It is similar to how we do pseudo rate constants. We make one reactant so large that it basically doesn't affect the reaction rate, enabling us to just study the other reactant as if it is the only thing that affects the rate. Same thing with liquids and solids. They are in such high excess that the...
by Maayan Epstein 14B
Sat Mar 16, 2019 10:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Stability of reactants and products
Replies: 2
Views: 7

Re: Stability of reactants and products

The equilibrium constant will tell you this. If K is greater than 10^3 then it favors the products, meaning that the products are much mnore stable than the reactants. If K is smaller than 10^-3 then it favors the reverse reaction and the reactants are much more stable than the products. If K is bet...
by Maayan Epstein 14B
Sat Mar 16, 2019 10:11 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst in molecularity
Replies: 1
Views: 7

Catalyst in molecularity

When you report the moleculairty of a step, and that step includes a catalyst, do you include the catalyst in the molecularity or not? Thanks!
by Maayan Epstein 14B
Sat Mar 16, 2019 10:07 pm
Forum: *Enzyme Kinetics
Topic: Collision theory
Replies: 2
Views: 13

Re: Collision theory

The reaction that is least likely to occur has higher molecularity (i.e. third order reactions are less likely to occur than second order which are less likely to occur than first order). This is because two things need to happen for a reaction to occur: the molecules need to collide in the proper o...
by Maayan Epstein 14B
Sat Mar 16, 2019 10:02 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Test 2 Question 5
Replies: 5
Views: 50

Re: Test 2 Question 5

The second method is correct. I am not sure how you solved the first method, but you use the equation ln(k2/K1)= RT(1/T2 -1/T1) to solve for K2. Then you use K2 to find the concentration of H+. The equilibrium concentration of H+ at 10 degrees C for a neutral solution (we know it is neutral because ...
by Maayan Epstein 14B
Sat Mar 16, 2019 9:54 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Positive or Negative Ecell Values
Replies: 4
Views: 14

Re: Positive or Negative Ecell Values

Do you mean Ecell or E (standard) cell? Because E (with the circle on the top symbolizing standard conditions) is different from Ecell.
The Nernst equation shows the relationship between these: Ecell = E(standard) - (R*T)/(n*F) * lnQ

I hope that helps!
by Maayan Epstein 14B
Sat Mar 16, 2019 9:52 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: net rate of reaction
Replies: 1
Views: 5

Re: net rate of reaction

I am not totally sure what you mean by net rate of reaction, but for each elementary step the rate should look the same. For example: Step 1: A + B ----> C Step 2: C -----> D Both should have rate = k[reactants] so for step 1 use rate constant k1: rate = k1[A][B] and for step 2 use rate constant k2:...
by Maayan Epstein 14B
Sat Mar 16, 2019 9:50 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 4
Views: 21

Re: Catalysts

I think that it is better to just know the rule that a catalyst is something that appears in the beginning and end of the reaction (is not consumed, and is not an intermediate).
by Maayan Epstein 14B
Tue Mar 05, 2019 2:05 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Changing concentration to change rate
Replies: 2
Views: 24

Changing concentration to change rate

How does changing the concentration of different species affect the rate of the reaction? If a reactant has a coefficient of 1 and you double its concentration and the rate of reaction doubles then this is a first order reaction. If a reactant has a coefficient of 1 and you double its concentration ...
by Maayan Epstein 14B
Tue Mar 05, 2019 2:03 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Zero, First, and Second Order reactions
Replies: 2
Views: 22

Zero, First, and Second Order reactions

I still a bit confused on what exactly order of reaction means and how this interacts with different species. For example, in the reaction: H2 + I2 ----> 2HI. Why is this a second order reaction? Is it because each reactant has a coefficient of 1 and 1+1 equals 2, or because the product has a coeffi...
by Maayan Epstein 14B
Tue Mar 05, 2019 1:59 pm
Forum: General Rate Laws
Topic: Unique Rate
Replies: 4
Views: 23

Re: Unique Rate

You can calculate the unique rate by dividing the rate of reaction of a specific species by its coefficient. This is the unique rate of reaction, and will be the same rate if you use any of the species in the reaction.
by Maayan Epstein 14B
Tue Mar 05, 2019 1:57 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.7 or finding rates of decomposition
Replies: 2
Views: 26

Re: 15.7 or finding rates of decomposition

If this is 15.7 in the 6th edition, I noticed that on the syllabus Dr. Lavelle did not include this in the practice problems to do.
by Maayan Epstein 14B
Tue Feb 26, 2019 6:20 pm
Forum: Balancing Redox Reactions
Topic: Basic redox reactions
Replies: 3
Views: 26

Basic redox reactions

How do you balance the H+ in a cell when it is basic?
I don't understand how to convert H+ into OH- and balance from there (what order of steps should I take?)

Thank you!
by Maayan Epstein 14B
Tue Feb 26, 2019 3:53 pm
Forum: Balancing Redox Reactions
Topic: redox homework question
Replies: 3
Views: 19

redox homework question

Hi, in homework question 14.1 in the 6th edition, I am supposed to name the elements that undergo either oxidation or reduction. The answer solution does not include oxygen in it, even though it is oxidized. Can someone explain? H+ (aq) +cr2o7^2- (aq) +c2H5OH (aq) --> Cr^3+ (aq) + C2H4OH (aq) + H2O ...
by Maayan Epstein 14B
Mon Feb 25, 2019 8:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing agent/oxidizing agent
Replies: 5
Views: 31

Reducing agent/oxidizing agent

When something is a "reducing agent", does this mean it gets oxidized or reduced? Furthermore, does this mean it is the cathode or the anode?
by Maayan Epstein 14B
Sun Feb 17, 2019 8:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta S of reaction
Replies: 1
Views: 27

delta S of reaction

Why is delta S of reaction different than delta S molar/delta S of formation of a substance? For example, in problem 9.55 (6th edition), we use an appendix to look up the delta S of formation (listed as delta S molar) of a substance, i.e. NH3, and subtract from it the delta S molar of its reactants ...
by Maayan Epstein 14B
Mon Feb 11, 2019 4:27 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Buffers
Replies: 4
Views: 36

Buffers

How do buffers work in acid base reactions? Can someone explain, thank you!
by Maayan Epstein 14B
Sun Feb 10, 2019 6:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent ionization vs percent deprotonation
Replies: 3
Views: 44

Percent ionization vs percent deprotonation

Is there a difference between calculating percent ionization and percent deprotonation? Are they the same thing?

Thanks!
by Maayan Epstein 14B
Wed Feb 06, 2019 1:10 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Thermochemistry // Thermodynamics
Replies: 2
Views: 37

Re: Thermochemistry // Thermodynamics

Thermodynamics is work, heat, and energy (this includes enthalpy and entropy), whereas thermochemistry is about the bonds and the molecular structure. I think of thermochemistry as the microscopic level, whereas thermodynamics is bigger picture.
by Maayan Epstein 14B
Tue Feb 05, 2019 6:32 pm
Forum: Ideal Gases
Topic: Ideal gas constant R
Replies: 9
Views: 84

Re: Ideal gas constant R

Thank you for the responses!
by Maayan Epstein 14B
Mon Feb 04, 2019 5:02 pm
Forum: Ideal Gases
Topic: Ideal gas constant R
Replies: 9
Views: 84

Ideal gas constant R

When do I plug in the ideal gas constant, R, as 0.0825, and when do I plug it in as 8.314?
Not sure when to use which!
by Maayan Epstein 14B
Mon Feb 04, 2019 4:42 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Homework Problem 8.21 in 6th edition: Q=mcat
Replies: 1
Views: 27

Homework Problem 8.21 in 6th edition: Q=mcat

Homework problem 8.23 in the 6th edition textbook states: "A calorimeter was calibrated with an electric heater, which supplied 22.5 kJ of energy as heat to the calorimeter and increased the temperature of the calorimeter and its water bath from 22.45 C to 23.97 C. What is the heat capacity o...
by Maayan Epstein 14B
Fri Feb 01, 2019 12:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpies
Replies: 5
Views: 41

Re: Enthalpies

Enthalpy refers to the change in the internal heat of the system at constant pressure (qp).
by Maayan Epstein 14B
Fri Feb 01, 2019 12:21 pm
Forum: Calculating Work of Expansion
Topic: Reversible Expansion
Replies: 3
Views: 40

Re: Reversible Expansion

Something else to note is that this equation is only used when temperature is constant, because all the other q equations involve a delta T, whereas this one is just T by itself.
by Maayan Epstein 14B
Fri Feb 01, 2019 12:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: CP/V
Replies: 2
Views: 35

Re: CP/V

Cp and Cv are constants. Cp=20.8 and Cv=12.5.
They are used in the q (or delta H) equations, where qp (q at constant pressure) = nCp(delta T), and qv (q at constant volume) = nCv(delta T).
Hope that helps!
by Maayan Epstein 14B
Tue Jan 22, 2019 11:10 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in Pressure, Volume, and Concentration
Replies: 2
Views: 36

Re: Changes in Pressure, Volume, and Concentration

Also something to be aware of is that if there is an increase in pressure but the same number of moles of gas on each side of the equation, then nothing happens to the system. If the question states that the PARTIAL pressure of one of the chemicals in the reaction increases, and not the total pressu...
by Maayan Epstein 14B
Tue Jan 22, 2019 11:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Second deprotonation
Replies: 3
Views: 47

Second deprotonation

Do we need to know second deprotonation for tomorrow's test?
Some of the homework problems for chapter 12 mention it (i.e. 6th edition 12.81)
Thanks!
by Maayan Epstein 14B
Thu Jan 17, 2019 3:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How temperature affects K
Replies: 4
Views: 37

Re: How temperature affects K

Thank you Kim for your response! Super helpful.
Do you know why heat and temperature are not treated in the same way in terms of how they affect equilibrium? It seems like both heat and temperature would affect the rate that the molecules hit each other.
by Maayan Epstein 14B
Thu Jan 17, 2019 3:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How Ka and Kb relate to each other
Replies: 1
Views: 28

How Ka and Kb relate to each other

If Kc of the forward reaction is the inverse of the Kc of the reverse reaction, then does this mean that in an acid-base chemical equilibrium reaction, the conjugate acid would dissociate at the inverse rate that the conjugate base would accept a proton (in the opposite direction)? If my logic is fl...
by Maayan Epstein 14B
Thu Jan 17, 2019 3:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How temperature affects K
Replies: 4
Views: 37

How temperature affects K

Why does changing temperature change the equilibrium constant K, but changing pressure, heat, and concentration does not?
by Maayan Epstein 14B
Thu Jan 17, 2019 3:20 pm
Forum: Student Social/Study Group
Topic: ICE Table
Replies: 5
Views: 36

Re: ICE Table

The reason that you can do an approximation where you "ignore" the x in the denominator, is because if the K value is smaller than 10^-3, then the x when multiplied out by this k value will be very negligible. So, instead of going through the whole process and doing the quadratic formula i...
by Maayan Epstein 14B
Thu Jan 10, 2019 1:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How to use ICE tables
Replies: 5
Views: 70

How to use ICE tables

How do I know what to plug into ice tables? For example, I know that I can plug in molarity to find initial, change, and equilibrium. Will this work for pressure too?
Thanks!
by Maayan Epstein 14B
Thu Jan 10, 2019 1:24 pm
Forum: Ideal Gases
Topic: Identifying gases in equilibrium via pictures
Replies: 2
Views: 21

Re: Identifying gases in equilibrium via pictures

Thank you so much for your response! It makes much more sense now. I guess another way to think about it is that the reactants are the diatomic (stuck together) gas molecules and the products are the single, free floating molecules.
by Maayan Epstein 14B
Thu Jan 10, 2019 12:16 pm
Forum: Ideal Gases
Topic: Identifying gases in equilibrium via pictures
Replies: 2
Views: 21

Identifying gases in equilibrium via pictures

For this week's homework, one of the problems (11.7 in the 6th edition) shows a picture of four flasks with gas molecules in them. The gas is an unknown diatomic molecule, X2. Part a of the questions asks: "Which flask represents the point in time at which the reaction has reached equilibrium?&...

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