## Search found 30 matches

Sat Mar 17, 2018 10:24 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Concept of Second Law of Thermodynamics
Replies: 6
Views: 533

### Re: Concept of Second Law of Thermodynamics

deltaS = q + w
Sat Mar 17, 2018 10:20 pm
Forum: Phase Changes & Related Calculations
Topic: Standard States
Replies: 2
Views: 279

### Re: Standard States

It's in standard state if the substance is at 25 C and 1 atm.
Sat Mar 17, 2018 10:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Friday Section Test 2
Replies: 2
Views: 242

### Friday Section Test 2

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

The galvanic cell given is:

O3/O2, OH- and O3, H+/O2.
Sun Mar 11, 2018 10:24 pm
Forum: First Order Reactions
Topic: Equation variations
Replies: 9
Views: 603

### Re: Equation variations

The equations will give you the same thing; the second is just rearranged using log rules.
Sun Mar 11, 2018 10:20 pm
Forum: Second Order Reactions
Topic: the slope
Replies: 12
Views: 825

### Re: the slope

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.
Sun Mar 11, 2018 10:14 pm
Forum: Second Order Reactions
Topic: Half life
Replies: 6
Views: 524

### Re: Half life

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...
Sun Mar 04, 2018 2:16 pm
Forum: General Rate Laws
Topic: Integrated Rate Laws when a =/= 1
Replies: 4
Views: 302

### Re: Integrated Rate Laws when a =/= 1

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.
Sun Mar 04, 2018 2:13 pm
Forum: General Rate Laws
Topic: How to know when to use which formula?
Replies: 2
Views: 222

### Re: How to know when to use which formula?

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...
Fri Mar 02, 2018 1:24 pm
Forum: General Rate Laws
Topic: Integrated Rate Laws when a =/= 1
Replies: 4
Views: 302

### Integrated Rate Laws when a =/= 1

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...
Sun Feb 25, 2018 11:40 pm
Forum: General Rate Laws
Topic: Differential rate law
Replies: 3
Views: 237

### Re: Differential rate law

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.
Sun Feb 25, 2018 11:22 pm
Forum: General Rate Laws
Topic: Reaction Rates [ENDORSED]
Replies: 2
Views: 187

### Reaction Rates[ENDORSED]

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?
Sun Feb 25, 2018 9:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 4
Views: 328

### Cell Diagrams

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).
Mon Feb 19, 2018 12:02 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: The Daniell Cell
Replies: 4
Views: 234

### Re: The Daniell Cell

What makes the Daniell cell different from a general galvanic cell?
Sun Feb 18, 2018 5:37 pm
Forum: Balancing Redox Reactions
Replies: 2
Views: 198

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-?
Tue Feb 13, 2018 7:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat
Replies: 1
Views: 140

### Heat

Why is heat not a state function?
Sat Feb 10, 2018 11:13 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.75 [ENDORSED]
Replies: 1
Views: 167

### Re: 9.75[ENDORSED]

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 ...
Sat Feb 10, 2018 10:51 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.63
Replies: 2
Views: 184

### Re: 9.63

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...
Sat Feb 10, 2018 1:06 am
Forum: Balancing Redox Reactions
Topic: Midterm Topics [ENDORSED]
Replies: 2
Views: 183

### Midterm Topics[ENDORSED]

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.
Thu Feb 01, 2018 11:41 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Mass and molar entropy
Replies: 3
Views: 377

### Re: Mass and molar entropy

The heavier the molecules are, the more vibrational energy levels they have available. The more energy levels they have, the greater the entropy.
Thu Feb 01, 2018 11:32 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy change
Replies: 4
Views: 262

### Re: Entropy change

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.
Thu Feb 01, 2018 11:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: The value of Cp
Replies: 8
Views: 622

### Re: The value of Cp

The Cp and Cv values can be found on page 281 in the textbook. Cp is the heat capacity of the system at constant pressure while Cv 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.
Fri Jan 26, 2018 12:12 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Question regarding 8.39 homework question
Replies: 5
Views: 323

### Re: Question regarding 8.39 homework question

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...
Thu Jan 25, 2018 11:43 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calculating heat (q)
Replies: 4
Views: 818

### Re: Calculating heat (q)

Whether you use mCsdeltaT or nCmdeltaT is dependent on what's given initially. mCsdeltaT is used when your information is in terms of grams while nCmdeltaT is used when you information is in terms of moles.
Thu Jan 25, 2018 10:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What are the types of calorimeters we learned about/ covered in class?
Replies: 4
Views: 294

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

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.
Sat Jan 20, 2018 4:55 pm
Forum: Calculating Work of Expansion
Topic: Formula for reversible expansion
Replies: 2
Views: 116

### Re: Formula for reversible expansion

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(Vfinal/Vinitial), they rewrote it with the conversion 101.325 J = 1 L*atm to get 8.3145 J/(K*mol).
Sat Jan 20, 2018 4:46 pm
Forum: Calculating Work of Expansion
Topic: Irreversible and Reversible Processes
Replies: 4
Views: 294

### Irreversible and Reversible Processes

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?
Sat Jan 20, 2018 4:42 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Difference between Closed and Isolated
Replies: 10
Views: 1323

### Re: Difference between Closed and Isolated

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...
Sun Jan 14, 2018 10:50 am
Forum: Phase Changes & Related Calculations
Topic: Irreversible process vs reversible process
Replies: 4
Views: 200

### Re: Irreversible process vs reversible process

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...
Sun Jan 14, 2018 10:32 am
Forum: Phase Changes & Related Calculations
Topic: Expansion and change in pressure
Replies: 4
Views: 241

### Re: Expansion and change in pressure

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...
Sun Jan 14, 2018 10:17 am
Forum: Phase Changes & Related Calculations
Topic: Heat Capacity vs. Specific Heat Capacity
Replies: 3
Views: 564

### Re: Heat Capacity vs. Specific Heat Capacity

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...