## Search found 30 matches

Sat Mar 17, 2018 4:28 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Chapter 14 # 107
Replies: 1
Views: 238

### Re: Chapter 14 # 107

I think in this problem you use K instead of Q because when we are given a pH, we assume that the concentrations are at equilibrium. Basically, if a solution is at a certain pH, the concentrations are not going to change at that temperature.
Sat Mar 17, 2018 4:19 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Q7b Lyndon's Review
Replies: 6
Views: 346

### Re: Q7b Lyndon's Review

The big K is the equilibrium constant for step 1, and that is used for this approach since we assume that this step in the reaction is working in equilibrium, as a result of step 2 being the slow reaction. The little k is the rate constant.
Thu Mar 15, 2018 5:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams for Concentration Cells
Replies: 1
Views: 141

### Re: Cell Diagrams for Concentration Cells

If the cell potential is greater than 0, the concentration of the cathode should be greater than the concentration of the anode
Thu Mar 15, 2018 4:41 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Q6
Replies: 2
Views: 247

### Re: Test 2 Q6

If the oxidation number is going from +1 to 0, it is gaining an electron, and doesn't that mean it is being reduced? I thought the reducing agent was the substance that was oxidized?
Wed Mar 14, 2018 2:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Q6
Replies: 2
Views: 247

### Test 2 Q6

For question 6B, it asks to identify the reducing agent of a redox couple that forms a galvanic cell. The redox couple is Pt2+/Pt and AgF/Ag,F-
I know that the oxidizing agent is Pt2+ and for the reducing agent I thought it was F- but that answer was incorrect. Can someone explain this to me?
Wed Mar 14, 2018 2:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculating Standard Cell Potential
Replies: 2
Views: 191

### Re: Calculating Standard Cell Potential

Yes exactly! You should get the same answer for both methods, it just depends on which method you prefer (I personally prefer using Ecell=Ecathode-Eanode just because it's easier for me)
Tue Mar 13, 2018 4:11 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation
Replies: 1
Views: 168

### Arrhenius Equation

In class we went over the arrhenius equation as being k=Ae^-Ea/RT, with a being the "pre-exponential factor" but in homework problems we never actually use that equation in that form. I've only seen it used in this form: ln (k2/k1)=-Ea/RT(1/T1-1/T2) in order to find the activation energy, ...
Tue Mar 13, 2018 3:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Drawing Reaction Profiles
Replies: 3
Views: 237

### Re: Drawing Reaction Profiles

You would make a table like the ones that were drawn in lecture. Energy is the y-axis and the progress of the reaction is the x-axis. You would start with the reactants and draw the energy barrier(s) and then end with the products, most often with a lower energy than the reactants
Sat Mar 10, 2018 1:52 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Example 15.8 [ENDORSED]
Replies: 2
Views: 209

### Example 15.8[ENDORSED]

I noticed that the book used the slope of the function in order to calculate the activation energy. Will we have to use a linear regression tool as stated in the textbook or would that information usually be given to us?
Thu Mar 08, 2018 10:33 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63 units and reaction order
Replies: 1
Views: 158

### Re: 15.63 units and reaction order

I'm pretty sure you are correct with the units. I got L mol-1s-1 as well for the units!
Thu Mar 08, 2018 10:30 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.61
Replies: 1
Views: 150

### Re: 15.61

We actually haven't gone over this equation in lecture yet, but you basically just plug in the given k values and temperatures into this equation:
ln (k'/k)=(Ea/R)(1/T-1/T'), and you would just rearrange the equation to get the activation energy.
Thu Mar 08, 2018 10:25 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Self Test 15.11B
Replies: 1
Views: 123

### Re: Self Test 15.11B

In lecture, we went over a problem like this but the only reason there was a 2 was because the rate=(1/2)d[NO2]/dt since there is a stoichiometric coefficient of 2 for NO2 in the given reaction. Therefore, to get d[NO2]/dt by itself we multiplied the other side by 2. That's the only reason I think t...
Thu Mar 08, 2018 10:16 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8011
Views: 1401333

### Re: Post All Chemistry Jokes Here

Why did the acid go to the gym?
To become a buffer solution!
Mon Feb 26, 2018 9:50 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8011
Views: 1401333

### Re: Post All Chemistry Jokes Here

What did the scientist say when he found 2 isotopes of helium? Hehe
Mon Feb 26, 2018 2:59 pm
Forum: Zero Order Reactions
Topic: 15.9b
Replies: 2
Views: 217

### 15.9b

Can someone explain to me why you are supposed to divide the units by (mol A)/L for the first-order reaction?
Mon Feb 26, 2018 2:39 pm
Forum: General Rate Laws
Topic: Unique Rate [ENDORSED]
Replies: 4
Views: 252

### Re: Unique Rate[ENDORSED]

Is the unique rate the same in every reaction whether you use values of the reactants or products?
Sun Feb 18, 2018 11:22 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation (log vs. ln)
Replies: 5
Views: 2110

### Nernst Equation (log vs. ln)

I know that we discussed in class the difference between using log and ln in the nernst equation, but is there any specific reason we would choose one over the other? or does it not matter?
Sun Feb 18, 2018 11:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.37
Replies: 1
Views: 115

### Re: 14.37

First you need to write both of the half reactions, the reduction reaction and the oxidation reaction. Each half reaction in this case has a standard potential of 0. So when you plug that into the equation for the standard potential of the cell (subtracting that of the anode from the cathode potenti...
Sun Feb 18, 2018 10:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: The Daniell Cell
Replies: 4
Views: 212

### Re: The Daniell Cell

I think it's more important that you just understand galvanic cells in general, and I don't think you need to remember the specifics of the Daniell Cell or other examples, just know how they work
Fri Feb 09, 2018 9:11 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.85
Replies: 1
Views: 176

### 9.85

For part c and d of this question, how do we know whether positional or thermal disorder is dominant? I know that in d, the solution manual says that the surroundings participate in the solution process only as a source of heat, so the entropy change of the surroundings is primarily a result of the ...
Sun Feb 04, 2018 7:28 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: 9.33
Replies: 1
Views: 143

### 9.33

Is it safe to assume that for any given reaction, if the the number of moles of gas is less on the product side, the entropy should decrease?
Sun Feb 04, 2018 7:16 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: 9.25
Replies: 2
Views: 191

### 9.25

For these types of questions, will you always have to figure out the number of different possible orientations of the molecule by drawing it out?
Thu Feb 01, 2018 8:28 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.19
Replies: 4
Views: 361

### Re: 9.19

For the third part of the example in the book, How would we know to use Cp,m= 4R? And why didn't they use that value to calculate the step 1 of heating the liquid acetone?
Sun Jan 28, 2018 10:34 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Third Law of Thermodynamics
Replies: 4
Views: 247

### Re: Third Law of Thermodynamics

yes, so it is basically defining absolute zero on the entropy scale and this is important because the entropy determined relative to this point is the absolute entropy.
Sun Jan 28, 2018 10:16 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: More Entropy vs. Less Entropy
Replies: 3
Views: 199

### Re: More Entropy vs. Less Entropy

I'm not sure if we've gone over this in class, but I think the principle of minimum energy and the entropy maximum principle should help you understand this concept more! Also, I think referring to entropy as disorder is probably causing more misunderstanding about this topic.
Sun Jan 28, 2018 9:40 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Replies: 3
Views: 104

It's basically just saying that the entire internal energy of a system is not all convertible into useful work. The portion that can be converted into useful work can be referred to as the available energy, and the portion that cannot is the unavailable energy. And I believe entropy is the measure o...
Sat Jan 20, 2018 3:01 pm
Forum: Calculating Work of Expansion
Topic: Formula for reversible expansion
Replies: 2
Views: 116

### Re: Formula for reversible expansion

R is just the gas constant from the ideal gas law (PV=nRT), so it would be 8.314 J K^-1 mol^-1)
Sun Jan 14, 2018 7:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard State
Replies: 1
Views: 96

### Re: Standard State

I don't think there's a specific way to determine the standard state of an elements, but it is pretty self explanatory for the most part. For example, the standard state for the noble gases would be gas, for metals and metalloids it would be solid (for the most part), and for halogens it varies, but...
Sun Jan 14, 2018 7:01 pm
Forum: Phase Changes & Related Calculations
Topic: problem 8.29
Replies: 2
Views: 184

### Re: problem 8.29

Yes, in general molar heat capacity increases with molecular complexity, because with more complex molecules, there are more possible bond vibrations that can absorb the added energy, making the heat capacity higher for the molecule.
Sun Jan 14, 2018 6:52 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Delta values
Replies: 3
Views: 152

### Re: Delta values

I think it depends on the problem. I do know that delta h f (standard enthalpy of formation) is always in kj/mol. Most delta h values given in tables are in kj/mol, because they don't assume any values in the reaction. However, if the problem specifies mass or moles, you would likely multiply it by ...