CHEMISTRY COMMUNITY

Yea Eun Lee 1H

Calculate K and delta G at 298 K for the following redox reaction. Hint: Identify the two half-reactions and show a balanced equation to receive full credit. Use: MnO4- + 8H+ + 5e- -> Mn2+ + 4H2O E= -1.49 V Br2 + 2e- -> 2Br- E= +1.07 V How come when calculating for K, we assume that the redox equati...

Yea Eun Lee 1H

Do we incorporate catalysts when writing the rate law?

Yea Eun Lee 1H

rate-determining step is used when you know which elementary reaction is the slow step. steady state approximation is used when you don't know the rate-determining step or when there's multiple rate-determining steps

Yea Eun Lee 1H

Calculate the standard potential for the following reaction using the reduction potentials on the last page of the test: Fe3+ + 3e- ->Fe

I found two related half-reactions: Fe3+ + e- -> Fe2+ and Fe2+ + 2e- -> Fe
but I dont know what to do next. How do I solve this problem?

Yea Eun Lee 1H

What material do we need to understand from Section 15.12 (Collision Theory) in the textbook? do we have to know the formulas?

Yea Eun Lee 1H

Will we be given whether the reaction is a slow or fast reaction? If so, how do we find that out?

Yea Eun Lee 1H

For the net rate of formation of products, is it rate of formation - rate of consumption or rate of consumption - rate of formation (or does this even matter at all?)

Yea Eun Lee 1H

What is the role of the stopping syringe in the stopped flow technique? How is this technique supposed to measure the change of concentrations over time?

Yea Eun Lee 1H

For increasing oxidizing power, do we organize the elements from low to high standard reduction potentials then?

Yea Eun Lee 1H

It doesn't matter how you multiply as long as everything cancels out. However, it's most convenient to multiply by the least common factor

Yea Eun Lee 1H

My TA also mentioned that it's fair game for derivations to appear on the final exam. However, if I were you, I'd focus on other concepts first and when there's time left, look over the derivations. Remembering the derivations will also help you understand the equations better

Yea Eun Lee 1H

List of half reactions should be provided on the test with their standard potentials

Yea Eun Lee 1H

Will we be explicitly told that the redox reaction is specifically in a acidic/basic solution? Or will we have to recognize this on our own based on the given ions?

Yea Eun Lee 1H

A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and
undergoes an expansion against 0.5 atm external pressure until its volume doubles.
Calculate the work involved in Joules.

How come for this problem we don't use the equation -nRT ln V2/V1?

Yea Eun Lee 1H

you'd also use this equation if some information is given about W (like any info about number of ways a molecule can exist)

Yea Eun Lee 1H

how come delta u is zero for an isothermal expansion?

Yea Eun Lee 1H

Yup, enthalpy is a state function, which explains why we are able to use Hess's law to calculate the reaction enthalpy.

Yea Eun Lee 1H

Calculate the entropy of vaporization of acetone at 296 K with an external pressure of 1 bar. The molar heat capacity of liquid acetone is 127 J/K-mol, its boiling point is 329.4 K, and its enthalpy of vaporization is 29.1 kJ/mol. Step 1: change in entropy= C ln(T2/T1)= 127 * ln (329.4/296)= +13.5 J...

Yea Eun Lee 1H

Do we have to read and understand Box 8.1 in the textbook for the midterm? It talks about the differential thermal analysis.

Yea Eun Lee 1H

I understand mathetmatically how we find the equations for Cv and Cp, but I'm having a bit of trouble with this conceptually. How come Cv is change in internal energy/change in temperature? Why can't it be the change in enthalpy/change in temperature (and vice versa for Cp)?

Yea Eun Lee 1H

Will the problems explicitly say whether or not the system is reversible/irreversible? Or will we have to identify them? Especially for the midterm?

Yea Eun Lee 1H

How come Dr. Lavelle doesn't like associating entropy with disorder?

Yea Eun Lee 1H

How come we don't consider the contribution of vibrational energy when calculating the molar internal energy (Um)?

Yea Eun Lee 1H

But when an ideal gas expands isothermally, volume increases and pressure decreases. Since volume increased, the system did work on the surroundings...so wouldn't work be non-zero, making the change in internal energy non-zero as well?

Yea Eun Lee 1H

The integral is used for deriving the equation for finding work in a reversible gas expansion. The integral is used to find the area of the curve in a volume vs. pressure graph (you can find that on p 266 of the textbook). The graph is curve because in a reversible gas expansion, the external pressu...

Yea Eun Lee 1H

Is it possible to show an infinitesimal change of the gas expansion experimentally (like has anyone found a video of an experiment that shows a reversible gas expansion)? Or is the concept of reversibility theoretical?

Yea Eun Lee 1H

According to the textbook, the "change in internal energy is the same regardless of the path taken between the same initial and final states"

So does that mean the change in internal energy would be the same regardless if the gas expanded reversibly or irreversibly? If so, why?

Yea Eun Lee 1H

We'll be given those values for the test, right?

Yea Eun Lee 1H

Can someone explain why this equation is true? I'm having some difficulty understanding it.

change in U= qP + w= qP= change in H

Yea Eun Lee 1H

8.11 A piston confi nes 0.200 mol Ne(g) in 1.20 L at 25 'C. Two experiments are performed. (a) The gas is allowed to expand through an additional 1.20 L against a constant pressure of 1.00 atm. (b) The gas is allowed to expand reversibly and isothermally to the same fi nal volume. Which process does...

Yea Eun Lee 1H

As long as the substance is in its most stable form, I'm pretty sure you can use compounds (combination of elements)for the standard enthalpy formation

Yea Eun Lee 1H

I think a calorimeter is a closed system...but can anyone think of an example that works as an isolated system?

Yea Eun Lee 1H

Just out of curiosity, is it possible to find the enthalpy change of a reaction using bond enthalpies for reactants/products that have resonance structures?

CHEMISTRY COMMUNITY

Search found 33 matches

Winter 2013 Midterm Q7

Rate Laws and Catalysts

Re: Slow Step Vs. Steady State Approximation

Test 2 Q7

Section 15.12

Slow vs Fast Reactions

Net rate of formation of products

Stopped Flow Technique

Re: Test 2, Q5

Re: Balancing number of electrons

Re: Derivations

Re: Finding half reactions

Recognizing a redox reaction in acidic or basic solution

Midterm Q4A

Re: S=klnW

Re: Delta U as 0

Re: Is enthalpy a state function?

Box 9.6

Differential Thermal Analysis

Conceptual Help on Cv vs Cp

Solving Reversible vs irreversible [ENDORSED]

Entropy and Disorder

Equipartition Theorem

Re: isothermal system

Re: The integral equation

Reversible vs Irreversible

U for Reversible & Irreversible Expansion

Re: Heat Capcity for Water

Equation from Friday Lecture

Homework 8.11

Re: Standard Reaction Enthalpy

Re: Closed System

Using Bond Enthalpies for Resonance Structures