CHEMISTRY COMMUNITY

Grace Han 2K

On test 2, #7, we have to use Gibbs free energy to calculate the standard potential because standard potentials cannot be added since they are not a state function. However, when it asks to calculate standard cell potential in #6D, we just add -1.24V + 2.04V to get the answer. I dont understand when...

Grace Han 2K

Im confused as to where n(overall)=6. Can you please explain?

Grace Han 2K

Go to Dr. Lavelle's page, and under Math Assistance, there is a Kinetic file. There is a detailed graph on page 3.

Grace Han 2K

Also, rate constants are dependent on temperature and activation energy.

Grace Han 2K

For rxn rate vs time, the graph will have a horizontal line and then abruptly fall to zero when all the reactants are consumed.
For the integrated zero rate law, it will look similar to the graph of first-order integrated rate law where the slope= -k

Grace Han 2K

For this question, I got a different answer and was wondering if my method is incorrect.

Part A:

rate= 1/3 d[B]/dt= 1/3[0.018 mol L^-1/ 3min]= 0.002mol L^-1 min^-1
first order rate= k[A]
.002mol L^-1 min^-1= k[0.015 mol L^-1]
k= 0.13 min^-1

The textbook answer is k=0.17 min^-1

Grace Han 2K

I don't trust atoms......

I heard they make up everything.

Grace Han 2K

My TA said that it is a good idea to know, or at least understand the derivations.

Grace Han 2K

I think the units of k is the same units as concentration.

Grace Han 2K

H2O is added to balance the rxn if you have to balance Oxygen, however there are no oxygen present, so you could skip that step and add H+.

Grace Han 2K

Does anyone know how to write a cell diagram for this equation?

Grace Han 2K

C2H5OH Oxygen is going to have an ON (Oxidation number) of -2 unless its in a peroxide. Hydrogen is going to have an ON of +1 if its with nonmetals. Now we have to solve for Carbon's ON When adding up all of the ON for C2H5OH, it should equal zero. ____/2 (Carbon)+ 6x +1(Hydrogen) + -2(Oxygen)= O Th...

Grace Han 2K

In order to make iced-tea, a 50.0g ice cube at 0.00C is added to 250 ml of tea at 20.0C. What is final temp of the iced tea once it has reached thermal equilibrium. Assume that no heat is transferred to or from the surroundings. The density of water and iced tea is 1.00g/mL over the range of 0-20 C....

Grace Han 2K

There is no class but there is a review session from 2-330 if youre interested.

Grace Han 2K

I figured it out.

Delta S= nCvln(T2/T1)= 3.854mol (5/2R) (ln 326/298)= 4.31

Delta S tot = 22.27 + 4.31= 26.6 J/K

Grace Han 2K

A sealed container has two compartments: one is 7.60 L filled with 83.07g of Ar gas, and the other 5.30L filled with 35.82g of Ne gas a) What is deltaS System if the separating divider is removed and the two gases are allowed to mix? Assume constant temperature at 25 degrees C. I got 22.27J/k b) Wha...

Grace Han 2K

gas>> liquid >> solid If a rxn has only gas molecules, then you can subtract the number of moles from the product to the reactant. If it is negative, then the change in entropy is negative. If it is positive, then the change in entropy is positive for the forward reaction. example 2CO(g) + O2(g) -->...

Grace Han 2K

When calculating for the standard gibbs free energy of formation, what are the units? Is it Kj or Kj/mole? I thought the answer would be in kilojoules or joules because the moles cancel out when you multiply with n, but the answer in self-test 9.21A has it in kj/mol. In example 9.14, its answer is l...

Grace Han 2K

Hi, Im not sure if I understood your question clearly but basically, the initial temperature is not 0 degrees C. The T must be converted into Kelvin and so you have to add 273K to the given Celsius to get Kelvin for the temperature.

Grace Han 2K

For reversible, you can assume that the total change in entropy should equal to zero. For example, change in entropy for the system could be calculated using nRln(V2/V1). Change in entropy for the surroundings could be calculated by: deltaU=q+w deltaU is equal to zero for an isothermal expansion for...

Grace Han 2K

I also had a question regarding reversible vs irreversible reactions.

For chapter 19, Self test 9.17a & b, the question gives us both change in volume and change in pressure, but when solving it why do we only use the change in volume and not the pressure?

Grace Han 2K

The textbook uses the "disorder" when defining entropy, but Dr. Lavelle avoids using the term "disorder" in his lectures. Should we try to avoid using this term for future references? For example if the midterm/final were to ask to define entropy. And also, can someone explain en...

Grace Han 2K

Can someone explain what the 1st, 2nd, and 3rd law of thermodynamics mean (how they differ)?

Grace Han 2K

Sure, I could send you a picture of today's notes if you email me with your phone number. My email address is gracehan0105@gmail.com. I'll try to respond as quickly as possible.

Grace Han 2K

Hey, my TA advised I do mostly chapter 9 homework problems for homework #3 so I am assuming that this week (HW #4) should be all Chapter 9 problems.

Grace Han 2K

I’m not sure if this is correct, but I think in general, for combustion, Hydrocarbons combust with oxygen to produce carbon dioxide and liquid water.

It would be great if someone could clarify!

Grace Han 2K

How do you know if an element or compound is in its standard state? My notes says that while calculating standard rxn enthalpy, to make sure everything is in standard state and if it is not, take into account of phase change.

Grace Han 2K

I would highly recommend studying the heating and melting curve, and should be able to draw it out to help you visualize the problem regarding phase changes.

Grace Han 2K

When you are solving for the change in temperature, it does not matter whether you use Kelvin or Celsius because you will get the same answer.

Grace Han 2K

In the textbook page 264, there's a self-test problem 8.1A and I keep getting a different answer than the answer provided. Water expands when it freezes. How much work does 100. g of water do when it freezes at and pushes back the metal wall of a pipe that exerts an opposing pressure of 1070 atm? Th...

Grace Han 2K

if you are using the change in temperature, the change is the same whether it is in Kelvin or Celsius,

For example, if Initial temp is 283 K and final temp is 293 K, then change in temp is 10 K.
Now if we change it to Celsius, then initial is 10 C and final is 20 C. The change in temp is 10 C.

Grace Han 2K

I had a similar question and found this link helpful: https://chemistry.stackexchange.com/questions/47150/what-is-the-difference-between-enthalpy-h-and-heat-q It says, "Enthalpy and heat are entirely different things. Enthalpy is a function of state. If you know the state of a system, you know ...

Grace Han 2K

I think the length of the heating curve just represents the time it takes to reach a specific temperature.

CHEMISTRY COMMUNITY

Search found 33 matches

Calculate standard potential, Gibbs free

Re: Test #2 #7

Re: graph of 0 order

Re: Rate Constant k

Re: graph of 0 order

Re: 15.29

Re: Post All Chemistry Jokes Here

Re: Knowing rate law equations

Re: Units of k [ENDORSED]

Re: 14.5 part d

Re: HW #14.3 d

Re: 14.1 (b)

Calculating final temperature

Re: No class on Wednesday?

Re: Practice Midterm Karen Leung #8 [ENDORSED]

Practice Midterm Karen Leung #8 [ENDORSED]

Re: entropy sign

Standard Gibbs Free Energy of Formation (Units)

Re: Example 9.10

Re: Reversible vs Irreversible reactions

Re: Reversible vs Irreversible reactions

Entropy and Disorder

Thermodynamics 1st 2nd 3rd Law

Re: Would someone be able to share today's lecture notes please?

Re: homework/reading schedule

Re: H2O as a liquid or vapor

Standard state

Re: Material in Book but not in Lectures

Re: K vs C

Ch 8.1 Solving work

Re: Celsius the same as Kelvin? [ENDORSED]

Re: Clarification

Re: Heating Curve