CHEMISTRY COMMUNITY

Joanne Guan 1B

deltaS = q + w

Joanne Guan 1B

It's in standard state if the substance is at 25 C and 1 atm.

Joanne Guan 1B

For #6 on the test, why is the reducing agent O₂?

The galvanic cell given is:

O₃/O₂, OH^- and O₃, H⁺/O₂.

Joanne Guan 1B

The equations will give you the same thing; the second is just rearranged using log rules.

Joanne Guan 1B

The integrated zero-order rate law is [A] = -kt so the slope would be -k.
The integrated first-order rate law is ln[A] = ln[A]₀ - kt, so the slope would be -k.
The integrated second-order rate law is 1/[A] = 1/[A]₀ + kt, so the slope is k.

Joanne Guan 1B

If you're talking about finding the time for when the concentration is 1/16 of the initial concentration, you would use the integrated second-order rate law which is: 1/{A] = 1/[A] 0 + kt [A] = (1/16)[A] 0 Subbing that into the 1/[A] part would give you 1/((1/16)[A] 0 ), and if you reorganize it, yo...

Joanne Guan 1B

Because to find the first order integrated rate law, we integrate (-1/a)d[A]/dt = -k[A], where a is the coefficient of the reactant.

Joanne Guan 1B

I'm not really sure what you're trying to ask, but here are some hopefully helpful points. Zero-order integrated rate law: [A] = - kt + [A] 0 First-order integrated rate law: ln[A] = -kt + ln[A] 0 Second-order integrated rate law: 1/[A] = kt + 1/[A] 0 These can be found on the constants and equation...

Joanne Guan 1B

For a reaction like 2H 2 O 2 --> 2H 2 O + O 2 , should we integrate a rate law using a = 2 or just use the ones given to us on the constant sheet? I know that the integrated first-order rate law for this would be ln[A] = ln[A] 0 - 2kt, but I remember being told to just use the a = 1 rate law. Can so...

Joanne Guan 1B

For a reaction aR --> bP, the initial reaction rate is k[R]ⁿ. I believe in class we used this to compare two or more initial rates, but there could be more uses discovered later on in lecture.

Joanne Guan 1B

I know that even if a reactant is decreasing, we should write the rate as positive. Why do we want to work with positive reaction rates?

Joanne Guan 1B

How do you know what goes in what order for a cell diagram? For example, for #14.13 part c, the question gives
Cl₂ (g) --> 2Cl^- (aq) and
2H⁺ (aq) --> H₂ (g).

Joanne Guan 1B

What makes the Daniell cell different from a general galvanic cell?

Joanne Guan 1B

In Example 14.1 in the book, the solution adds H⁺ to balance the extra H⁺ from the H₂O. In Example 14.2, the solution adds OH^- instead. How do you know whether to add H⁺ or OH^-?

Joanne Guan 1B

Why is heat not a state function?

Joanne Guan 1B

I'm not sure if there's any mathematical way of discerning the number of microstates there are, but I usually just visualize and count the different orientations a molecule can have. To explain, imagine cis -MX 2 Y 4 replacing all the X atoms with Y atoms. There's only one microstate because M must ...

Joanne Guan 1B

The book gives definitions for thermodynamically stable/unstable compounds. A stable compound has a negative standard Gibbs free energy, meaning the reaction goes toward the compound. An unstable compound has a positive standard Gibbs free energy, meaning the reaction goes toward the elements. The q...

Joanne Guan 1B

I know that chapters 8, 9 and 11 will be covered for the midterm, but will chapter 14 (electrochemistry) be on it? I noticed the constants sheet has stuff from electrochemistry.

Joanne Guan 1B

The heavier the molecules are, the more vibrational energy levels they have available. The more energy levels they have, the greater the entropy.

Joanne Guan 1B

Yes, entropy is always increasing because even if an endothermic reaction occurs, the energy had to have come from somewhere in order to perform the reaction.

Joanne Guan 1B

The C_p and C_v values can be found on page 281 in the textbook. C_p is the heat capacity of the system at constant pressure while C_v is the heat capacity at constant volume. R is the ideal gas constant, and you would typically use R in the form 8.3145 J*K^-1*mol^-1 for these calculations.

Joanne Guan 1B

When ice is melting, the temperature doesn't change until it is fully melted. That means you can only calculate the change from 0C to 20C until the ice is fully melted and becomes water. Therefore, you have to use the specific heat capacity of water. Now, if the ice were at -10C, then you would calc...

Joanne Guan 1B

Whether you use mC_sdeltaT or nC_mdeltaT is dependent on what's given initially. mC_sdeltaT is used when your information is in terms of grams while nC_mdeltaT is used when you information is in terms of moles.

Joanne Guan 1B

I believe that the system would be whatever's inside the calorimeter and the surroundings would be the calorimeter itself since the calorimeter is absorbing the heat.

Joanne Guan 1B

The ideal gas constant from PV = nRT is given as 0.08206 (L*atm)/(mol*K). For R to be more applicable to w = -nRT*ln(V_final/V_initial), they rewrote it with the conversion 101.325 J = 1 L*atm to get 8.3145 J/(K*mol).

Joanne Guan 1B

I understand that a reversible process is one that can be reversed by an infinitely small change and an irreversible process is expansion against an external pressure that differs by a finite amount from the system's pressure. Can someone give examples for these two processes?

Joanne Guan 1B

Closed systems are able to exchange energy with their surroundings, but they cannot exchange matter. Isolated systems cannot exchange energy or matter. For example, if you were to put hot water in a normal bottle, the water will start to cool down to room temperature. However, if you put hot water i...

Joanne Guan 1B

An irreversible process is expansion against an external pressure such that an infinitesimal change in the external pressure does not reverse the direction. A reversible process is expansion that can be reversed by an infinitesimal change. For example, in an irreversible process, a piston can only m...

Joanne Guan 1B

Volume and pressure are inversely related only if there are no other factors in play. However, because of the temperature change, you cannot only consider volume change when trying to figure out whether pressure increases or decreases. The answer given makes sense because as temperature drops, molec...

Joanne Guan 1B

Heat capacity is defined as the amount of energy needed to raise the temperature of a substance by 1°C. Specific heat capacity is defined as the amount of energy needed to raise the temperature of ONE GRAM of a substance by 1°C. As you can see, the specific heat capacity can be applied to all amount...

CHEMISTRY COMMUNITY

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Re: Concept of Second Law of Thermodynamics

Re: Standard States

Friday Section Test 2

Re: Equation variations

Re: the slope

Re: Half life

Re: Integrated Rate Laws when a =/= 1

Re: How to know when to use which formula?

Integrated Rate Laws when a =/= 1

Re: Differential rate law

Reaction Rates [ENDORSED]

Cell Diagrams

Re: The Daniell Cell

Add H+ or OH-

Heat

Re: 9.75 [ENDORSED]

Re: 9.63

Midterm Topics [ENDORSED]

Re: Mass and molar entropy

Re: Entropy change

Re: The value of Cp

Re: Question regarding 8.39 homework question

Re: Calculating heat (q)

Re: What are the types of calorimeters we learned about/ covered in class?

Re: Formula for reversible expansion

Irreversible and Reversible Processes

Re: Difference between Closed and Isolated

Re: Irreversible process vs reversible process

Re: Expansion and change in pressure

Re: Heat Capacity vs. Specific Heat Capacity