CHEMISTRY COMMUNITY

Sam Joslyn 1G

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?

Sam Joslyn 1G

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?

Sam Joslyn 1G

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)=(E_a/R)*(1/T₁-1/T₂)

Sam Joslyn 1G

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...

Sam Joslyn 1G

ln2/k=t_1/2 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 t_1/2=1/k[A]₀

Sam Joslyn 1G

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.

Sam Joslyn 1G

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...

Sam Joslyn 1G

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.

Sam Joslyn 1G

Why is E^o an intensive property?

Sam Joslyn 1G

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.

Sam Joslyn 1G

E^o is an intensive property, so you never multiply it by the molar proportions of reactants and products.

Sam Joslyn 1G

While both are indeed correct, my TA instructed us to always put it in the reduction form just to create continuity with the E^o values

Sam Joslyn 1G

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) ?

Sam Joslyn 1G

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")

Sam Joslyn 1G

Physical chemists must be rich because they have so many joules!! Hehe

Sam Joslyn 1G

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

Sam Joslyn 1G

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.

Sam Joslyn 1G

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...

Sam Joslyn 1G

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...

Sam Joslyn 1G

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.

Sam Joslyn 1G

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...

Sam Joslyn 1G

Will the equation sheet we had for Test #1 also be the equation sheet we will have on the midterm?

Sam Joslyn 1G

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).

Sam Joslyn 1G

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?

Sam Joslyn 1G

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...

Sam Joslyn 1G

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!

Sam Joslyn 1G

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?

Sam Joslyn 1G

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...

Sam Joslyn 1G

I'm glad I am not the only person with this problem! Thank you.

Sam Joslyn 1G

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-]=K_w/[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?

Sam Joslyn 1G

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?

Sam Joslyn 1G

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

Sam Joslyn 1G

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 ...

Sam Joslyn 1G

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...

CHEMISTRY COMMUNITY

Search found 34 matches

Ways to practice pre-equilibrium approach

Concept of molar entropy

Re: Arrhenius Equation.

Re: Pseudo Reaction

Re: 15.31 6th Edition

Re: Graph of ln[A] against time

Re: oxidizing power vs reducing power

Re: Half life- zero order

Eo an Intensive Property

Re: chapter 6O??

Re: Standard Potential

Re: Anode reaction

Order of Cell Diagram

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

Re: Post All Chemistry Jokes Here

Re: Trends

Re: 4J.15

Change in free energy for a reaction at equilibrium

Re: 7th edition 4I. 9

Re: Temperature Dependence of K

Re: Reversible Processes

Equation sheet for midterm

Re: Heat Capacity

Delta U=0 for isothermal compression?

Heat Capacity of a Calorimeter, Question 4A.11

Re: Writing equations for weak acids/bases

Question about problem 6D.15(b)

ACIDS AND BASES: What to do with very dilute acid

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

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

Finding K in 5I.7

Re: Giving Qc or Qp when asked for Q

Re: Multiplying Equilibrium Constants?

Re: Equilibrium in a System