Search found 41 matches

by Elizabeth Gallmeister 1A
Mon Mar 11, 2019 12:31 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equilibrium reaction mechanisms
Replies: 1
Views: 55

Re: Pre-equilibrium reaction mechanisms

As we went over in lecture today, we can assume that the fast step preceding the rate-determining step is at an approximate equilibrium, because the product gets bottlenecked by the slow reaction. From there, we can use the K from the pre-equilibrium reaction in order to sub in values into the rate ...
by Elizabeth Gallmeister 1A
Mon Mar 11, 2019 12:25 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.27
Replies: 3
Views: 223

Re: HW 15.27

Going off the earlier answer, once you find k, make sure you plug that into the right equation! Since this is a first order reaction, we know that ln[A]=−kt+ln[A]0. However, had it been a zero order or second order reaction, the equation would have been different.
by Elizabeth Gallmeister 1A
Mon Mar 11, 2019 12:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-determining step
Replies: 1
Views: 38

Re: Rate-determining step

The rate from the rate-determining step must match the overall rate of the reaction. If the coefficients of the rate-determining step are not in line with the powers of the overall rate law for the reaction, then it's not the rate-determining/slow step.
by Elizabeth Gallmeister 1A
Mon Mar 04, 2019 8:47 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Which Rate to Use When Finding K? HW Chapter 15 #19, 6th Edition
Replies: 2
Views: 65

Re: Which Rate to Use When Finding K? HW Chapter 15 #19, 6th Edition

You can use any of the experiments when solving for k; it should be the same value for each because the concentrations of reactants should have the same effect on rate no matter what concentration they are at. Are you sure the k in the manual varied from experiment to experiment?
by Elizabeth Gallmeister 1A
Mon Mar 04, 2019 8:46 pm
Forum: General Rate Laws
Topic: Order of Reaction
Replies: 6
Views: 110

Re: Order of Reaction

And the order could be lower than the amount of reactants, because some reactants may be raised to the zeroth power, whereas others may be raised to higher powers than that.
by Elizabeth Gallmeister 1A
Mon Mar 04, 2019 8:45 pm
Forum: Zero Order Reactions
Topic: 7A 15
Replies: 4
Views: 89

Re: 7A 15

If you look at experiment 1 and 4, the only concentration that changes is for C. Yet, if you compare the initial rate for both experiments, they're the same value (2.0). So, we can see that the change in concentration of C has no bearing on the rate of the reaction, and therefore it is raised to the...
by Elizabeth Gallmeister 1A
Mon Feb 25, 2019 9:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt bridge
Replies: 2
Views: 53

Re: Salt bridge

The ions moving across the salt bridge travel in the opposite direction of the electrons. So, if electrons travel from left (anode) to cathode (right), then the ions will move from cathode to anode.
by Elizabeth Gallmeister 1A
Mon Feb 25, 2019 9:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing agent/oxidizing agent
Replies: 5
Views: 99

Re: Reducing agent/oxidizing agent

Right, the reducing agent is oxidized because it facilitates and allows for the reduction of the other species. One way to think about it is the oxidation produces the electrons transferred to actually reduce the other species.
by Elizabeth Gallmeister 1A
Mon Feb 25, 2019 4:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 7th edition, 6M.1 [ENDORSED]
Replies: 1
Views: 89

7th edition, 6M.1 [ENDORSED]

A student is given a standard Cu|Cu2+ half cell and another half cell containing unknown metal M, forming cell M|M+||Cu2+|Cu. Cell potential is -0.689V. What's the value of E(M2+/M)? For this problem, how can we tell whether Cu is reduced or oxidized? And why does it ask for the value of E for M2+ a...
by Elizabeth Gallmeister 1A
Wed Feb 20, 2019 11:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6th edition, 6L3
Replies: 1
Views: 46

6th edition, 6L3

How can we tell which side is the anode and which is the cathode? It doesn't always follow the convention. Like with part a, it did follow the convention with Ni|Ni2+||Ag+|Ag where Ni was oxidized. But for part b, it didn't follow convention with C|H2|H+||Cl-|Cl2|Pt because H2 was involved in the re...
by Elizabeth Gallmeister 1A
Wed Feb 20, 2019 4:39 pm
Forum: Balancing Redox Reactions
Topic: 7th edition, 6K3 pt d
Replies: 1
Views: 40

7th edition, 6K3 pt d

For the reaction in part (d), Cl2 -> HClO + Cl2, how do we balance this skeletal equation and write the half reactions? I know that CL2 is oxidized, but what is reduced?
by Elizabeth Gallmeister 1A
Wed Feb 20, 2019 4:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: positive E value?
Replies: 1
Views: 38

positive E value?

Today in lecture, Lavelle said that a positive standard reduction potential value means that the reaction/process is spontaneous. How can we make that connection/assumption?
by Elizabeth Gallmeister 1A
Fri Feb 15, 2019 9:29 am
Forum: Calculating Work of Expansion
Topic: S=0
Replies: 12
Views: 420

Re: S=0

deltaS is also zero when the start conditions and end conditions of a process are the same, because entropy is a state function.
by Elizabeth Gallmeister 1A
Tue Feb 12, 2019 9:07 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: How Much of the Outline Do I Need to Know?
Replies: 2
Views: 104

Re: How Much of the Outline Do I Need to Know?

For seventh edition, it's all the problems up to section 4.7.
by Elizabeth Gallmeister 1A
Mon Feb 11, 2019 4:59 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 3/2R and 5/2R
Replies: 2
Views: 64

Re: 3/2R and 5/2R

For this midterm, I think the only time you'll use them is in deltaS = nC ln (T2/T1), depending on if it's constant pressure or volume.
by Elizabeth Gallmeister 1A
Mon Feb 11, 2019 4:56 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: pressure effect on entropy
Replies: 2
Views: 83

pressure effect on entropy

Why does entropy decrease when pressure increases?
by Elizabeth Gallmeister 1A
Wed Feb 06, 2019 8:38 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Equation help!
Replies: 1
Views: 60

Re: Equation help!

If it's not under constant pressure, it's probably an isothermal, reversible process. We use the equation w = -nRT ln(V2/V1) in that case.
by Elizabeth Gallmeister 1A
Wed Feb 06, 2019 8:36 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible vs. Irreversible
Replies: 1
Views: 60

Re: Reversible vs. Irreversible

Yes, irreversible processes have constant pressure whereas reversible processes have very small changes in pressure. For irreversible expansion, temperature is not constant along the pathway. Reversible processes are isothermal because temperature does not change along the pathway. Isothermal, rever...
by Elizabeth Gallmeister 1A
Tue Feb 05, 2019 11:22 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: temperature of a reversible reaction
Replies: 3
Views: 73

Re: temperature of a reversible reaction

And from there, if deltaT is zero, it follows that deltaU = 0 and therefore q = -w.
by Elizabeth Gallmeister 1A
Mon Feb 04, 2019 9:18 am
Forum: Calculating Work of Expansion
Topic: Integral calculations
Replies: 4
Views: 97

Re: Integral calculations

I think we just took the integral of the graph of external pressure and volume in order to derive the equation for work at constant pressure for irreversible expansion. I think as long as you can recognize the conditions at which you use w = -Pex (deltaV), you don't need to take any integrals.
by Elizabeth Gallmeister 1A
Fri Feb 01, 2019 8:32 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: w and q
Replies: 1
Views: 50

w and q

I know that deltaU = w + q, but is there a definitive way to know when each of these values is positive or negative? Like if work is done on the system vs done by the system, etc etc. Thanks!
by Elizabeth Gallmeister 1A
Thu Jan 31, 2019 6:29 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 7th edition, 4.15
Replies: 1
Views: 42

7th edition, 4.15

This question asks about the oxidation of zinc metal with hydrochloric acid to produce hydrogen gas and chloride ions. I found that the 8.5g piece of Zn is .130mol and the HCl is .400mol, but I'm not sure where to go from there. I know we need to find a q value for q = mc(deltaT) in order to find Tf...
by Elizabeth Gallmeister 1A
Wed Jan 30, 2019 7:45 pm
Forum: Calculating Work of Expansion
Topic: 4A.3 7th edition
Replies: 2
Views: 55

Re: 4A.3 7th edition

OH also I think the 7th edition solutions manual is wrong; it says 8 or something?? I'm pretty sure the 6th edition manual is right; it says 29. or maybe 28J.
by Elizabeth Gallmeister 1A
Wed Jan 30, 2019 7:43 pm
Forum: Calculating Work of Expansion
Topic: 4A.3 7th edition
Replies: 2
Views: 55

Re: 4A.3 7th edition

You're going to want to use the formula we learned in class today: w = -Pex (deltaV). Plugging in numbers, we get w = -(-2.00 atm) (1.5 cm)^2 (pi) (20 cm) From that, you get w = 283. atm. cm^3, which you then convert to J by multiplying by (1mL/1cm^3)(1L/1000mL)(101.325J/L.atm) = 29J Since it's comp...
by Elizabeth Gallmeister 1A
Mon Jan 28, 2019 9:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 7th Edit 4B5
Replies: 1
Views: 26

Re: 7th Edit 4B5

We haven't gone over this in class yet, but here's how I solved it. 1. A gain of 5.50 kJ of energy as heat means that q = +5.50 kJ 2. w = -Pex (deltaV) = -750. Torr (1 atm / 760 Torr) (1.846 L - .345 L) (101.325 J/L.atm) = -150. J We know that deltaU = w + q, so plugging in our numbers from steps 1 ...
by Elizabeth Gallmeister 1A
Sun Jan 27, 2019 7:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.9 7th Edition
Replies: 1
Views: 29

Re: 4A.9 7th Edition

You have to plug given values into q = mcΔT and set heat(water) = -heat(copper). For the first equation, heat(water) = 50.7g (4.18J/g°C)(Tf - 22°C) For the second, heat(copper) = 20g (.38J/g°C)(Tf - 100°C) We know that when the copper is placed in water, eventually the copper and water will reach th...
by Elizabeth Gallmeister 1A
Sun Jan 27, 2019 7:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW #8.29 (6th Edition)
Replies: 1
Views: 24

Re: HW #8.29 (6th Edition)

I know that molar heat capacity increases when a molecule becomes more complex, but I'm not entirely sure why.
by Elizabeth Gallmeister 1A
Wed Jan 23, 2019 8:52 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 6th edition, 4A3 pt c
Replies: 2
Views: 73

6th edition, 4A3 pt c

For part c, it asks what the change in internal energy in the system is. Based on the book, I assumed that delta U would be equal to work, which I found was 28. The 6th edition solution manual supports this but the key in the back of the 7th edition book lists the answer as 8J. Does anyone know whic...
by Elizabeth Gallmeister 1A
Wed Jan 23, 2019 8:45 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Knowing When to Approximate
Replies: 4
Views: 112

Re: Knowing When to Approximate

The general rule is that if K < 10^-3, we can approximate. The question of whether it's less than 5% of the original concentration just happens at the end to ensure the approximation was reasonable (which it typically is, when K < 10^-3)
by Elizabeth Gallmeister 1A
Mon Jan 21, 2019 9:12 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: calculating x cubically
Replies: 2
Views: 48

Re: calculating x cubically

I think the outline just referred to the assumption that we can make when K<10^-3 that x is negligible. Without this assumption, it would usually create a cubic equation.
by Elizabeth Gallmeister 1A
Mon Jan 21, 2019 9:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: how to determine if something is an acid or base
Replies: 4
Views: 76

Re: how to determine if something is an acid or base

Another way to figure it out is to see what the problem gives you, or other information that you can get from supplemental tables etc. You're usually given either a pH that implies that it's a base or acid, or there will be a given Ka or Kb which will also show you which it is.
by Elizabeth Gallmeister 1A
Mon Jan 21, 2019 9:08 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: percent ionization
Replies: 2
Views: 210

Re: percent ionization

For both, you use the concentration of conjugate base divided by the concentration of the initial acid, or concentration of conjugate acid divided by concentration of the original base, multiplied by 100. Since most acid base equations are in a one to one ratio, typically using [H3O+] for [A-] or [O...
by Elizabeth Gallmeister 1A
Fri Jan 18, 2019 8:27 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Weak Acids
Replies: 1
Views: 50

Re: Weak Acids

If an acid produces a negligible concentration of H3O+, less than 10^-7 M, then taking the negative log will result in a number greater than 7. However, since the autoprotolysis of water produces 10^-7 M H3O+, we can just consider the solution to be neutral, with pH 7. Even though there is a weak ac...
by Elizabeth Gallmeister 1A
Wed Jan 16, 2019 9:24 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.69 (6th Edition)
Replies: 3
Views: 49

Re: 11.69 (6th Edition)

Changing the concentration of a product or reactant in the gas or aqueous phase only changes the Q value, as the reaction will no longer be at equilibrium. K does not change.
by Elizabeth Gallmeister 1A
Tue Jan 15, 2019 4:14 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 11.33 6th edition
Replies: 2
Views: 68

Re: 11.33 6th edition

In order to calculate the reaction quotient, we need molarities, or concentrations of the products and reactants. We know that concentration is a measure of number of moles divided by volume, so we do just that: put moles over volume to find molarity of each.
by Elizabeth Gallmeister 1A
Tue Jan 15, 2019 4:13 pm
Forum: Ideal Gases
Topic: Water
Replies: 13
Views: 232

Re: Water

In a couple examples, we've seen water as a gas, such as the reaction of CO(g) + H2O(g) <-> CO2(g) + H2(g). In this case, its pressure would be included in our expression for K or Q.
by Elizabeth Gallmeister 1A
Mon Jan 14, 2019 4:12 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Module 4 Post Assessment #14
Replies: 3
Views: 101

Module 4 Post Assessment #14

15. The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will the following changes have on the equilibrium composition. a) Water is added. b) The partial pressure of CO2 is decreased. A. a) Decrease [C6H12O6] and [O2], b) Decrease [O2] B. a) Decrease...
by Elizabeth Gallmeister 1A
Sat Jan 12, 2019 5:54 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 6th edition, 5J11
Replies: 2
Views: 49

6th edition, 5J11

Part (b) concerns the equation X2 <-> 2X, where X is a halogen. Does X being a halogen tip us off as to whether the reaction is exothermic or endothermic? If yes, why?
by Elizabeth Gallmeister 1A
Tue Jan 08, 2019 8:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5H Problem #3 7th Edition
Replies: 2
Views: 57

Re: 5H Problem #3 7th Edition

In order to solve this problem, you have to consider two equations: 2BrCl -> Br2 + Cl2, with K1 = [Br2][Cl2]/[BrCl2]^2 H2 + Cl2 -> 2HCl, with K2 = [HCl]^2/[Cl2][H2] In order to determine K for the original equation, which we know is defined as [Br2][HCl]^2/[BrCl]^2[H2], we can simply multiply K1 * K...
by Elizabeth Gallmeister 1A
Mon Jan 07, 2019 4:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.13 Reaction Quotient [ENDORSED]
Replies: 3
Views: 85

Re: 11.13 Reaction Quotient [ENDORSED]

Also, by comparing Q and K, we can determine certain characteristics about the reaction not at equilibrium. If Q<K, then the reaction is going to tend towards the products in order to reach equilibrium. If Q>K, then the reaction tends towards the reactants. When Q=K, we know the reaction has reached...
by Elizabeth Gallmeister 1A
Mon Jan 07, 2019 4:56 pm
Forum: General Science Questions
Topic: Chem textbook
Replies: 3
Views: 138

Re: Chem textbook

I think it may have just been the online version that comes with the solutions manual. However, I think the syllabus confirmed that we just need the textbook and solutions manual in any form.

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