## Search found 30 matches

Sun Mar 18, 2018 1:18 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 2
Views: 221

### Concentration Cells

If we're given a concentration cell of Ag+ with 0.10 M of Ag+ and 2.0 M Ag+ solutions, would the anode or the cathode have the higher concentration?
Sun Mar 18, 2018 1:09 am
Forum: Calculating Work of Expansion
Topic: Reversible vs. Irreversible
Replies: 2
Views: 231

### Re: Reversible vs. Irreversible

Reversible processes are ideal and done an infinitesimally slow pace. Therefore, the max amount of work can be done.
On the other hand irreversible process are fast and at a constant P. The system loses some of its potential to do work.
Sun Mar 18, 2018 12:33 am
Forum: Calculating Work of Expansion
Topic: Work Equations: Which One to Use?
Replies: 3
Views: 259

### Re: Work Equations: Which One to Use?

Use w=-PdeltaV for irreversible systems (constant P) and use w = -nRTln (V2/V1) for reversible processes when P is not constant.
Sat Mar 17, 2018 11:29 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Replies: 5
Views: 342

In adiabatic systems, q=0 whereas in isothermal reactions deltaT = 0.
Sat Mar 17, 2018 10:56 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Standard enthalpy change
Replies: 2
Views: 230

### Re: Standard enthalpy change

So when you find q and divide that by 4 moles, that's the delta H per one mole of NO. You multiply that by 2 moles because in the overall reaction, 2 moles of NO is used.
Sat Mar 17, 2018 6:56 pm
Forum: Second Order Reactions
Topic: Half-lives of first order versus second order
Replies: 1
Views: 184

### Re: Half-lives of first order versus second order

The half life of a first order reaction does not depend on the initial concentration (half life= ln2/k) while the half life of a second order reaction does depend on the initial concentration (half life = 1/(k[A]initial). So you can use that method for first order reactions because the half life is ...
Sat Mar 17, 2018 6:39 pm
Forum: *Alkanes
Topic: Final
Replies: 13
Views: 1183

### Re: Final

We also went over line structures!
Sat Mar 17, 2018 5:14 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: equations
Replies: 1
Views: 187

### Re: equations

1st Law: You can also say that delta U = q + w.
2nd Law: delta S = q rev/T
3rd Law: lim T---> 0 K S = 0
Sat Mar 17, 2018 10:52 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 9.31 higher standard molar entropy
Replies: 1
Views: 217

### 9.31 higher standard molar entropy

The question asks whether ethene (ethylene) or an equivalent mass of polyethylene, a substance formed by the polymerization of ethylene has a higher standard molar entropy. The answer key states that it is ethylene because it's a gas whereas polyethylene is a solid. How would you be able to tell tha...
Sat Mar 17, 2018 1:18 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67b-- figuring out the chemical equation
Replies: 1
Views: 194

### Re: 8.67b-- figuring out the chemical equation

Since the question asks for the enthalpy of formation of CH3OH, the reactants would be its elements in their most stable form, which are C(gr), H2 (g), and O2 (g).
Sat Mar 17, 2018 12:51 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: qreaction and qcalorimeter
Replies: 3
Views: 361

### Re: qreaction and qcalorimeter

The heat released by a reaction is gained/absorbed by the calorimeter. So if the reaction releases 1 J of heat, q=-1. The calorimeter gains that 1 J of heat, which is why q for the calorimeter would be positive in this example.
Fri Mar 16, 2018 7:01 pm
Forum: Calculating Work of Expansion
Topic: What w equation to use
Replies: 5
Views: 385

### Re: What w equation to use

Use W = - P x ∆V for irreversible expansions (pressure is constant). On the other hand, use W = -nRT ln (V2/V1) or W = -nRT ln (P1/P2) for reversible expansions (pressure is not constant).
Fri Mar 16, 2018 6:16 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics Formulas for the Final
Replies: 2
Views: 278

### Re: Kinetics Formulas for the Final

In lecture, we only discussed the concepts behind the collision theory. I don't think we're going to be using the formula.
Fri Mar 16, 2018 6:13 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.65 Part b
Replies: 2
Views: 143

### Re: 15.65 Part b

The reaction is endothermic because the forward reaction has a higher activation energy than the reverse reaction. That means that the forward reaction requires more energy than the reverse. If you draw it out, the reactants are lower in energy than the products.
Fri Mar 16, 2018 5:16 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.69
Replies: 1
Views: 108

### 15.69

In this question, the reaction rate increases and the activation energy decreases because of the introduction of a catalyst. The question states that in practice, "the new pathway also has a different pre-exponential factor". Does that mean that changing the activation energy/adding a cata...
Fri Mar 16, 2018 5:03 pm
Forum: *Enzyme Kinetics
Topic: Catalysts and Intermediates
Replies: 5
Views: 630

### Re: Catalysts and Intermediates

Also, catalysts show up in the rate law while intermediates do not.
Tue Mar 13, 2018 8:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Q 7 (other form)
Replies: 1
Views: 125

### Re: Test 2 Q 7 (other form)

This is a path function so you can't just add the standard potentials together. You would have to find the standard Gibbs' Free energy reactions these two reactions and add them together. A. Fe2+(aq) + 2e- -> Fe(s) Eo=-0.44 V B. Fe3+(aq) + e- -> Fe 2+ (aq) Eo=0.77 V deltaGo = -nFEo -nFEo = -nFEo(A) ...
Tue Mar 13, 2018 7:58 pm
Forum: Calculating Work of Expansion
Topic: Irreversible and reversible
Replies: 1
Views: 87

### Irreversible and reversible

From a conceptual standpoint, why is irreversible work less than reversible?
Thu Mar 08, 2018 3:58 pm
Forum: Second Order Reactions
Topic: 15.27 vs 15.35
Replies: 3
Views: 275

### Re: 15.27 vs 15.35

I agree! For first order reactions, the half life is independent of initial concentration. However, for second order reactions, the half life depends on initial concentration.
Tue Mar 06, 2018 3:28 pm
Forum: First Order Reactions
Topic: Book Problem 15.21
Replies: 5
Views: 473

### Re: Book Problem 15.21

So to clarify, can we substitute mass for concentration? Or are we supposed to find the ratio of the initial and final concentration and use that to find the final mass?
Tue Mar 06, 2018 12:57 am
Forum: General Rate Laws
Topic: 15.19a Order
Replies: 6
Views: 233

### Re: 15.19a Order

I found the order for reactant B using experiments 1 and 3 instead because only the concentration of B is changed between those two reactions. I don't think you can compare experiments 2 and 3 because both the concentrations of A and B are changed. As illustrated by comparing experiments 1 and 2, ch...
Tue Mar 06, 2018 12:50 am
Forum: First Order Reactions
Topic: Zero-order vs. First-order reaction graphs
Replies: 5
Views: 821

### Re: Zero-order vs. First-order reaction graphs

For a zero order reaction, the concentration of reactant does not affect the rate. The zero order integrated rate law is [A] = -kt + [A]initial. Therefore, a zero order reaction is usually graphed as [A] vs. time, which should be a straight line. If it isn't a straight line then it is not a zero ord...
Sat Mar 03, 2018 8:01 pm
Forum: General Rate Laws
Topic: 15.17
Replies: 1
Views: 106

### Re: 15.17

To determine the rate order for each reactant, compare two experiments in which only the concentration of the reactant of interest is changing. For example, we can compare experiments 1 and 4 to determine the order for C. Only the initial concentration of C varies between these two experiments. I co...
Sat Mar 03, 2018 11:32 am
Forum: Zero Order Reactions
Topic: zero order slopes
Replies: 5
Views: 223

### Re: zero order slopes

The graph [A] vs. time has a negative slope because the concentration of reactants (A) decreases as the reaction progresses. For zero order reactions, the concentration doesn't affect the rate and [A] = -kt + [A]initial, so the slope = -k. Also, the k value should be positive.
Fri Mar 02, 2018 11:48 pm
Forum: Zero Order Reactions
Topic: Negative Order Reactions
Replies: 3
Views: 906

### Re: Negative Order Reactions

What would the units for k be for rate laws with fractional and/or negative orders?
Sat Feb 24, 2018 9:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: reducing power?
Replies: 5
Views: 232

### Re: reducing power?

Reducing power refers to how strong of a reducing agent a substance is. The more negative/lower a substance's reduction potential is, the more likely it will be oxidized (lose elections) and therefore be the stronger reducing agent.
Sat Feb 24, 2018 11:58 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.23 (c)
Replies: 3
Views: 134

### 14.23 (c)

This question asks us to write a cell diagram for the reaction, Cr2O7^2- (aq) + 14 H^+ (aq) + 6 Pu^3+ (aq) --> 6 Pu^4+ (aq) + 2 Cr^3+ (aq) + 7 H2O(l). The answer is Pt (s)| Pu^3+ (aq), Pu 4+ (aq) || Cr2O7^2- (aq), Cr^3+ (aq), H^+ (aq)| Pt (s). Is there any rule regarding where we place the protons i...
Sat Feb 24, 2018 11:42 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13(b)
Replies: 2
Views: 99

### Re: 14.13(b)

Does that mean that we prioritize putting it in the order of reactants to products before we consider the phases? I thought that we had to put aq closest to the salt bridge and solids on the outside.
Tue Feb 13, 2018 12:46 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Joe’s Review Session Last Problem
Replies: 1
Views: 116

### Re: Joe’s Review Session Last Problem

He asked us to find the deltaG for the formation of NH3 (assuming standard conditions) and gave us: deltaHf (NH3)= -46.11 kJ/mol deltaSm (NH3)= 192.45 J/K*mol deltaSm (H2)= 130.68 J/K*mol deltaSm (N2) = 191.61 J/K*mol We would use the reaction: N2 (g) + 3H2 (g) --> 2 NH3 (g) Since we're finding delt...
Sat Jan 20, 2018 10:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: standard enthalpy of formation [ENDORSED]
Replies: 4
Views: 197

### Re: standard enthalpy of formation[ENDORSED]

From what I understand, the reaction enthalpy measures the heat taken up or given off by any reaction with reactants and products. However, the enthalpy of formation measures the change in enthalpy between a substance and the elements that make up that substance in their standard state.