## Search found 34 matches

Wed Mar 13, 2019 1:48 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Ways to practice pre-equilibrium approach
Replies: 1
Views: 122

### Ways to practice pre-equilibrium approach

There aren’t many (if any) questions in the textbook that require us to use the pre-equilibrium approach to find a reaction mechanism that was discussed in class. Are there any other resources available that we can use to practice this method?
Tue Mar 12, 2019 11:05 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Concept of molar entropy
Replies: 2
Views: 349

### Concept of molar entropy

When one substance has a lower molar entropy than another, what exactly does that mean conceptually? Does it need less heat than the other substance to become more disordered?
Mon Mar 11, 2019 8:57 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation.
Replies: 4
Views: 198

### Re: Arrhenius Equation.

The Arrhenius equation would be used in any circumstance in which you are required to find the rate of a reaction from its activation energy and frequency factor. It can also be used to compare the rate of a reaction at different temperatures with the equation ln(k2/k1)=(Ea/R)*(1/T1-1/T2)
Mon Mar 11, 2019 8:41 pm
Forum: Experimental Details
Topic: Pseudo Reaction
Replies: 1
Views: 372

### Re: Pseudo Reaction

I'm not entirely sure if this answers your question, but a pseudo-first-order reaction is when you saturate the reaction with an excess of all the products but one, effectively making the change in concentrations of the saturated reactants negligible so that the rate is only dependent on the reactan...
Mon Mar 11, 2019 8:39 pm
Forum: First Order Reactions
Topic: 15.31 6th Edition
Replies: 3
Views: 174

### Re: 15.31 6th Edition

ln2/k=t1/2 for first-order reactions, so I'm guessing the the decay of iodine-131 is a first-order reaction. It would follow that you use this equation, not the half-life equation for second-order reactions which is indeed t1/2=1/k[A]0
Fri Mar 08, 2019 12:04 am
Forum: General Rate Laws
Topic: Graph of ln[A] against time
Replies: 4
Views: 178

### Re: Graph of ln[A] against time

This graph is referring to a first-order reaction. The plot of ln[A] vs. time is linear because first-order processes see the concentration of [A] undergo exponential decay; therefore, a graph of ln[A] for a first-order process would theoretically be linear with a slope=-k.
Fri Mar 08, 2019 12:02 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: oxidizing power vs reducing power
Replies: 3
Views: 1545

### Re: oxidizing power vs reducing power

oxidizing power is a species' ability to oxidize another species (this inherently means that the species with the oxidizing power is being reduced). reducing power is a species' ability to reduce something else (meaning that the species is being oxidized). Since reduction potential can be thought of...
Thu Mar 07, 2019 11:59 pm
Forum: First Order Reactions
Topic: Half life- zero order
Replies: 1
Views: 129

### Re: Half life- zero order

If a reaction is zero-order, it means that the rate is unaffected by the concentration of the reactant. Therefore, since rate determines half-life, if the reaction is zero-oder, that reactant has no effect on the half-life value.
Tue Feb 26, 2019 11:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Eo an Intensive Property
Replies: 1
Views: 79

### Eo an Intensive Property

Why is Eo an intensive property?
Tue Feb 26, 2019 11:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: chapter 6O??
Replies: 2
Views: 99

### Re: chapter 6O??

It is not required for the test this week. Everything we have learned in electrochemistry so far before the Nernst equation will be tested, I believe.
Tue Feb 26, 2019 10:27 am
Forum: Balancing Redox Reactions
Topic: Standard Potential
Replies: 2
Views: 120

### Re: Standard Potential

Eo is an intensive property, so you never multiply it by the molar proportions of reactants and products.
Tue Feb 26, 2019 10:23 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode reaction
Replies: 3
Views: 141

### Re: Anode reaction

While both are indeed correct, my TA instructed us to always put it in the reduction form just to create continuity with the Eo values
Tue Feb 26, 2019 10:19 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of Cell Diagram
Replies: 1
Views: 94

### Order of Cell Diagram

Let's say that there is a galvanic cell in which Cl2(g) is reduced to Cl-(aq) on the anodic side. In the cell diagram, does the order of these species matter? Is putting
II Cl2(g) I Cl-(aq)
different from
II Cl-(aq) I Cl2(g) ?
Thu Feb 21, 2019 3:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J.5) 7th edition of the textbook
Replies: 2
Views: 127

### Re: 4J.5) 7th edition of the textbook

All of the values in the Appendix actually depend on the temperature being 298K as this is the standard temperature used in chemistry (my TA called it "the scientific room temperature")
Thu Feb 21, 2019 3:20 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8245
Views: 1440102

### Re: Post All Chemistry Jokes Here

Physical chemists must be rich because they have so many joules!! Hehe
Wed Feb 20, 2019 1:39 pm
Forum: Balancing Redox Reactions
Topic: Trends
Replies: 5
Views: 176

### Re: Trends

I personally would just use the reaction as your way of finding out reducing/oxidizing agents. It can get confusing quite easily if you try to use rules of thumb, especially when the reactions involve d-block metals
Wed Feb 20, 2019 10:30 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J.15
Replies: 2
Views: 157

### Re: 4J.15

To solve this you would have to calculate the change in Gibbs free energy of the formation of the compound (so for PCl5 you would have the reaction P + 5/2(Cl2)-----> PCl5) then if delta G is negative it would be thermodynamically stable relative to its formation elements.
Mon Feb 18, 2019 1:41 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Change in free energy for a reaction at equilibrium
Replies: 3
Views: 118

### Change in free energy for a reaction at equilibrium

I am a little confused by the notes I took during Friday week 6's lecture, and was wondering if anyone could help clarify. I am confused as to whether the change in Gibbs free energy for a reaction at equilibrium is 0 or -RTln(K). And if it is the latter, how can a reaction at equilibrium have a cha...
Mon Feb 18, 2019 1:34 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 7th edition 4I. 9
Replies: 2
Views: 166

### Re: 7th edition 4I. 9

Since entropy is a state function, I believe it doesn't matter how exactly it increases (irreversible or reversible) so the change of enthalpy for the system is going to be the same for both expansions. The difference comes from the change in entropy of the surroundings. For a reversible process, th...
Mon Feb 18, 2019 1:26 pm
Forum: Van't Hoff Equation
Topic: Temperature Dependence of K
Replies: 5
Views: 269

### Re: Temperature Dependence of K

I believe Lavelle basically just described the Van't Hoff equation as concrete evidence for the statement made earlier in the course. Before, we had to just know that temperature changed K, but this equation shows how exactly it does that.
Wed Feb 06, 2019 9:55 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible Processes
Replies: 4
Views: 196

### Re: Reversible Processes

I've talked to a lot of TAs about this, and in general they say that questions on tests will specify whether it is reversible or irreversible. One rule of thumb that may not work all the time but has worked for me is that for ideal gas expansion problems, expansion is reversible if there is a non-co...
Tue Feb 05, 2019 11:53 pm
Forum: Administrative Questions and Class Announcements
Topic: Equation sheet for midterm
Replies: 3
Views: 222

### Equation sheet for midterm

Will the equation sheet we had for Test #1 also be the equation sheet we will have on the midterm?
Mon Jan 28, 2019 8:32 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity
Replies: 5
Views: 202

### Re: Heat Capacity

I think it would depend on the information the question gave you. I'm guessing that if it gave you the amounts of substances in moles they would wan the answer in the form of specific heat capacity (kJ*(degrees C)-1*g-1).
Mon Jan 28, 2019 8:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta U=0 for isothermal compression?
Replies: 1
Views: 93

### Delta U=0 for isothermal compression?

In the 7th edition of the textbook on page 258 (section 4B), it says that delta U = 0 "for the isothermal expansion (or compression) of an ideal gas. How can an ideal gas compress isothermally without any work?
Mon Jan 28, 2019 8:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat Capacity of a Calorimeter, Question 4A.11
Replies: 1
Views: 77

### Heat Capacity of a Calorimeter, Question 4A.11

Question 4A.11 (7th edition) asks for the heat capacity of a calorimeter given the information that 22.5 kJ of energy increases the calorimeters water bath from 22.45 degrees C to 23.97 degrees. since the formula for a calorimeter's heat capacity is C cal =-q*(delta)T, why is the answer a positive v...
Wed Jan 23, 2019 9:37 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Writing equations for weak acids/bases
Replies: 3
Views: 404

### Re: Writing equations for weak acids/bases

I don't think we need to include spectator ions. I believe that the format in which you wrote them would be totally acceptable as long as you get he message across and it's clear what you're talking about!
Wed Jan 23, 2019 9:25 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Question about problem 6D.15(b)
Replies: 2
Views: 86

### Question about problem 6D.15(b)

Question 6D.15(b) in the 7th Edition of Chemical Principles asks to find the pH of a system with 0.055 M AlCl3. I am confused as to how to proceed with this problem, because I do not know how this molecule can create hydronium or oxide ions. Did anyone figure this one out?
Wed Jan 23, 2019 9:21 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ACIDS AND BASES: What to do with very dilute acid
Replies: 2
Views: 109

### ACIDS AND BASES: What to do with very dilute acid

In lecture, Dr. Lavelle said that if the concentration of an acid introduced to a system is less than 10 -9 the pH should be regarded as 7 because the contribution of H30+ ions is so negligible. I'm wondering: when the concentration is between 10 -7 and 10 -9 , should we also neglect it or should we...
Tue Jan 15, 2019 10:12 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Question on Problem 6A.19C in 7th Edition
Replies: 3
Views: 94

### Re: Question on Problem 6A.19C in 7th Edition

I'm glad I am not the only person with this problem! Thank you.
Mon Jan 14, 2019 11:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Question on Problem 6A.19C in 7th Edition
Replies: 3
Views: 94

### Question on Problem 6A.19C in 7th Edition

This question asks to give the concentration of OH- in the solution that has a H3O+ concentration of 3.1 mol*L-1. Using the calculation [OH-]=Kw/[H30+], I got [OH-]=3.2*10-15 mol*L-1, but the book says 3.2*10-12 mol*L-1. Is there something I am missing?
Thu Jan 10, 2019 10:47 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Finding K in 5I.7
Replies: 3
Views: 125

### Finding K in 5I.7

Looking at the answer for 5I.7, it appears that a method for finding K is used that works with delta G and natural log. Should we be familiar with this method?
Thu Jan 10, 2019 9:10 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Giving Qc or Qp when asked for Q
Replies: 5
Views: 201

### Re: Giving Qc or Qp when asked for Q

It probably depends on the units that the question gives. If it gives the composition of the reaction in terms of pressure, use Qp, if it gives concentrations, use Qp
Thu Jan 10, 2019 9:08 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Multiplying Equilibrium Constants?
Replies: 1
Views: 90

### Re: Multiplying Equilibrium Constants?

When a chemical reaction can be composed of two or more other basic reactions, it's called a composite reaction. With these, you always multiply the two K's of the reactions that make up the composite reaction together as a rule. So I think that when it comes to composite reactions, always multiply ...
Thu Jan 10, 2019 9:03 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium in a System
Replies: 2
Views: 99

### Re: Equilibrium in a System

There are also reactions where saying that they reach equilibrium doesn't entirely make sense. This is a crude example, but when you burn wood (reactant), the product (ash, CO2, etc.) is never going to have a reverse reaction into wood. Some reactions go to completion, others reach a dynamic equilib...

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