CHEMISTRY COMMUNITY

Liz White 1K

Dr. Lavelle said that he would not ask us questions saying "derive this" on the final, but it would probably be good to know how the derivations of the rate laws work just so you can get a better understanding of the equations as a whole.

Liz White 1K

Could you indicate which equation you're referring to? They use the Nernst equation, which is in the textbook, as well as just a combination of Gibbs free energy from the half reactions to find the total Gibbs free energy.

Liz White 1K

So, to follow up on that question, is q_calorimeter just another way of saying q_surroundings? Since when a reaction loses heat, the surroundings gain that heat, and vice versa?

Liz White 1K

As you can see in the solutions manual for part b), you are supposed to put the oxidated ion over the oxidating ion when it comes to writing out the half reaction for the anode. Since Pb4+ is the result of Pb2+ losing electrons (oxidation is loss), Pb4+ is oxidated, so you divide Pb4+ / Pb2+.

Liz White 1K

To see how high the energy of the transition state is, just look at the graph of a reaction. The transition states are the peaks of each slope. Therefore, they are at the highest point of each step, so they have high energy.

Liz White 1K

What exactly does it mean when a process is adiabatic? And how does this affect the equations for internal energy and enthalpy?

Liz White 1K

Will someone explain to me why it is that q_reaction = -q_calorimeter? I don't understand why they are opposite of one another.

Liz White 1K

As a general formula to calculate the units of the rate constant for any reaction order n, you can use the equation:

units of k = (L/mol)^n-1 / s

Liz White 1K

We went over something similar to this in lecture today. The proposed structure for the activated complex is going to be the lewis structures of the two interacting species, aligned with one another with respect to the bonds broken and the bonds formed. Dr. Lavelle demonstrated this in lecture when ...

Liz White 1K

If you were asked to find the time it takes for the concentration of a substance to decrease to, say, 50% of its initial concentration, how would you set the equation up? I understand that you would apply it to ln[A]t = -kt + ln[A]0, but I'm not sure what to do with the 50%, and I always mess up wit...

Liz White 1K

What is the order of the reaction if the rate law includes division, such as rate = k*[A]/[B]? Would it be zero due to the fact that [A] has a power of 1 and [B] has a power of -1? Explain how this works please!

Liz White 1K

Yes, a reaction order can be negative. This means that the concentration has an inverse effect on the rate of reaction.

Liz White 1K

A pseudo first order reaction is just another way of saying a second order reaction but under more ideal conditions in order to simplify your calculations. If the concentration of one reactant is in great excess, you may assume that it is constant, allowing it to be ignored so that the rate therefor...

Liz White 1K

I know this question has been answered many times, but the simplest response is just to do dimensional analysis and multiply everything out. The units of k will be whatever makes the equation work out, so they differ according to the order of the reaction.

Liz White 1K

I would tell another chemistry joke, but it appears that all the good ones Argon.

Liz White 1K

I have a question about the variable n in the Nernst Equation. I have read that it correlates to the number of electrons transferred across the reaction. However, how is this calculated when there are 3 electrons added on the reactants side of the equation and two added to the products side? Do you ...

Liz White 1K

The question specifies that you have 125 grams of Krypton gas and 9.00 grams of Helium gas. Therefore, you may use the molar masses provided by a periodic table to calculate the number of moles. The molar mass of Krypton (Kr) is 83.80 g/mol and the molar mass of Helium is 4.00 g/mol.

Liz White 1K

As specified in the exercise, Container A contains monoatomic gas, and gas molecules are more free to bounce off of one another and create disorder compared to atoms that are "bound together." If an atom is more free to move around, it has greater entropy.

Liz White 1K

Can someone please explain the answer to this question in more detail? I don't understand why we use q=mcdeltaT + deltaH. Also, I plugged the values into this and got an incorrect answer.

Liz White 1K

My mistake, I meant to say Exercise 19.

Liz White 1K

In 11.19(b), I noticed that, when finding the equilibrium constant at 25 degrees C for the oxidation of carbon monoxide, 2CO(g) + O2(g) = 2CO2(g), the solutions manual says to subtract the entropy of formation of 2CO from the entropy of formation of 2CO2. In 11.19(a), the solutions manual just keeps...

Liz White 1K

I was wondering if anyone could explain exercise 9.19 for me? More specifically, why does the solutions manual describe that you must heat the water to 100 degrees and then cool it back down to 83 degrees Celsius when finding the standard entropy of vaporization of water at 85 degrees C? I don't und...

Liz White 1K

In summary, entropy is equal to the amount of disorder. Gibbs Free Energy is equal to the enthalpy minus the entropy times the temperature. We can use Gibbs Free Energy to determine whether or not a reaction is spontaneous, as a negative value of G will show spontaneity.

Liz White 1K

Yes--at equilibrium, the heat of the object must equal the heat of its surroundings.

Liz White 1K

In addition, when using the equation deltaS = qrev/T, you'll find that a lower temperature (in the denominator) will result in a greater overall entropy deltaS, and vice versa. So, 200K will result in a greater deltaS (deltaS = 200) than 800K (deltaS = 50). They are inversely proportional. To solve ...

Liz White 1K

If you think back to how Dr. Lavelle explained it in class, entropy is equal to the amount of disorder. Atoms in a gaseous state have more space to move around and bounce off one another compared to liquid and solid states. Therefore, a greater ability to bounce off of one another allows for more po...

Liz White 1K

The above responses are correct. To elaborate further, solving for G = 0 will give us the boiling point at which the liquid turns into a gas. The question asks us to find the temperature at which the vaporization of Br2 is spontaneous. Since we don't have enough information to solve for any negative...

Liz White 1K

With the information that we had, we were forced to solve for G = 0, which gives us the boiling point at which the liquid will become a gas. However, since it must be a gas, anything greater than 333K will be correct for this equation. Any higher temperature will result in G having a negative value,...

Liz White 1K

Exercise 8.43 mentions the connection between values such as heat of fusion and heat of vaporization, as well as heat capacities for different phases, and relates them to the appearance of phase change graphs. Can someone refresh me on how to read and interpret heating curves, and how to relate cert...

Liz White 1K

Exercise 8.53(b), when referring to a temperature increase in the calorimeter assembly, asks to calculate the internal energy change, deltaU, for the reaction (deltaU = q). At the end of the calculations, you find the number of moles and the value for C*deltaT separately, and you are supposed to use...

Liz White 1K

At first glance, I would say that it is an exothermic reaction because you are removing electrons from the atom, therefore releasing energy.

Liz White 1K

Is there anyone reading this who has Mackenzie as their TA? Does anyone know her preference?

Liz White 1K

: chemistry_joke_poster-r4f307c8a4a094e24b2bf07f8fcd1e116_wvk_8byvr_324.jpg (24.98 KiB) Viewed 10659 times

heheheheheheheh

Liz White 1K

When we turn in our 7 homework problems this week, are they supposed to be from Chapter 8 or Chapter 9, or both? I think I remember hearing Dr. Lavelle mention that we were currently in Chapter 9, but we've also done some of Chapter 8 this week.

Liz White 1K

The base is under a salt.

CHEMISTRY COMMUNITY

Search found 35 matches

Re: Derivations

Re: 14.33

Re: qreaction and qcalorimeter

Re: 14.31

Re: Transition States

Adiabatic Process

qreaction and qcalorimeter

Re: Units [ENDORSED]

Re: Chapter 15 #85

Calculating t using First Order Integrated Rate Law

Division in Rate Law

Re: Order less than 0

Re: Pseudo First Order Reaction

Re: Units of k [ENDORSED]

Re: Post All Chemistry Jokes Here

Calculating n in the Nernst Equation

Re: Practice Test, Question 3A

Re: Problem 9.35

Re: Enthalpy of fusion [ENDORSED]

Re: Exercise 11.17

Exercise 11.19

Exercise 9.19

Re: Define Entropy

Re: Heat Capacity

Re: 9.5

Re: 9.33 (a)

Re: Why should deltaG=0?

Re: Class Example

Homework Exercise 8.43 and Phase Changes

Homework Exercise 8.53

Re: Formation of a Cation from an Atom

Re: Homework Problems

Re: Post All Chemistry Jokes Here

Homework Problems

Re: Post All Chemistry Jokes Here