Search found 42 matches

by Wilson Yeh 1L
Fri Mar 16, 2018 10:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.101A
Replies: 3
Views: 104

15.101A

The answer is that the overall reaction is ClO- + I- --> IO-

How come Cl- isn't included with the products?
by Wilson Yeh 1L
Wed Mar 14, 2018 3:33 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary reactions
Replies: 6
Views: 234

Re: Elementary reactions

Elementary reactions basically make up an overall non-elementary reaction. Elementary reactions only involve a single step, whereas non-elementary reactions make up multiple single step elementary reactions. It should be noted that when dealing with elementary reactions, the coefficients DO matter f...
by Wilson Yeh 1L
Wed Mar 14, 2018 3:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Finding the slow step
Replies: 5
Views: 224

Re: Finding the slow step

The slow step is the rate determining step, so I think if you were to test a given set of steps, whichever one comes out to work and match the observed rate would be the slow step. At least that's what I'm pretty sure is the case, if I'm wrong someone feel free to correct me!
by Wilson Yeh 1L
Wed Mar 14, 2018 3:14 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Question about today's lecture?
Replies: 2
Views: 120

Question about today's lecture?

During lecture today, Dr. Lavelle went over a problem that involved identifying the correct mechanism according to the experimentally determined rate law. I understand everything about the problem, but I'm just curious about what happens if the tested step matches the observed rate. Like during lect...
by Wilson Yeh 1L
Wed Mar 07, 2018 6:09 pm
Forum: First Order Reactions
Topic: 15.37C
Replies: 5
Views: 431

15.37C

Sulfuryl chloride, SO2Cl2, decomposes by first-order kinetics, and k = 2.81 x 10 -3 min -1 at a certain temperature. (a) Determine the half-life for the reaction. (b) Determine the time needed for the concentration of SO2Cl2 to decrease to 10% of its initial concentration. (c) If 14.0 g of SO2Cl2 is...
by Wilson Yeh 1L
Tue Mar 06, 2018 5:21 pm
Forum: Second Order Reactions
Topic: 15.19 Part C
Replies: 3
Views: 238

Re: 15.19 Part C

So we have rate=k[A][B] 2 [C] 2 . The initial rate is given in units (mmolA)*L -1 *s -1 . Each of the concentrations are given in units mmol*L -1 . When we multiply all the concentrations of reactants together, we end up with units mmol*L -5 . By dividing (mmolA)*L -1 *s -1 by mmol 5 *L -5 to find ...
by Wilson Yeh 1L
Tue Mar 06, 2018 5:14 pm
Forum: Second Order Reactions
Topic: 15.19 Part C
Replies: 3
Views: 238

Re: 15.19 Part C

So we have rate=k[A][B] 2 [C] 2 . The initial rate is given in units (mmolA)*L -1 *s -1 . Each of the concentrations are given in units mmol*L -1 . When we multiply all the concentrations of reactants together, we end up with units mmol*L -5 . By dividing (mmolA)*L -1 *s -1 by mmol 5 *L -5 to find ...
by Wilson Yeh 1L
Tue Mar 06, 2018 4:48 pm
Forum: Second Order Reactions
Topic: 15.19 Part C
Replies: 3
Views: 238

15.19 Part C

Determine the value of the rate constant given the following values: A0: 1.25 B0: 1.25 C0: 1.25 Initial Rate: 8.7 Rate law: k[A][B]^2[C]^2 Using the concentrations given in mmol*L^-1 and rates given in mmol A*L^-1*s^-1, I got the value 2.85. However, in the answer the value is 2.85x10^12. Can someon...
by Wilson Yeh 1L
Fri Mar 02, 2018 4:17 pm
Forum: Zero Order Reactions
Topic: What role do coefficients play?
Replies: 3
Views: 133

What role do coefficients play?

How do coefficients relate to the order of a reaction? Like the coefficients in both the product and reactant? And how do the number of products produced relate to the order and rate?
by Wilson Yeh 1L
Fri Mar 02, 2018 3:59 pm
Forum: Zero Order Reactions
Topic: Will we need to know how to derive equations? [ENDORSED]
Replies: 9
Views: 351

Will we need to know how to derive equations? [ENDORSED]

For the final, will we need to know how to derive kinetic equations? Like using calculus to change the form of a given equation? Thanks!
by Wilson Yeh 1L
Wed Feb 28, 2018 4:24 pm
Forum: General Rate Laws
Topic: Why are rates always positive? [ENDORSED]
Replies: 1
Views: 83

Why are rates always positive? [ENDORSED]

How come rates aren't negative for consumption and positive for formation? I know it's convention to have it as positive but I'm just curious as to the background behind this.
by Wilson Yeh 1L
Thu Feb 22, 2018 8:09 pm
Forum: Balancing Redox Reactions
Topic: Does order matter?
Replies: 7
Views: 257

Does order matter?

Say my answer is Cl2 + H2O --> Cl- + HClO + H+, could I also write it as H20 + Cl2 --> HClO + Cl- + H+?

Is there a standard way to order this? Or does it not matter? Thanks!
by Wilson Yeh 1L
Thu Feb 22, 2018 6:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: What other elements could be used besides Pt?
Replies: 5
Views: 210

What other elements could be used besides Pt?

Or is Pt the only one you could use, assuming there's no solid in the cell and you need a solid?
by Wilson Yeh 1L
Wed Feb 21, 2018 6:36 pm
Forum: Balancing Redox Reactions
Topic: Self Test 14.1A [ENDORSED]
Replies: 1
Views: 94

Self Test 14.1A [ENDORSED]

Copper reacts with dilute nitric acid to form copper(II) nitrate and the gas nitric oxide, NO. Write the net ionic equation for the reaction. What would be the equation for this problem be? I set it up as Cu + HNO3 --> Cu(NO3)2 + NO but I'm pretty sure that's wrong. Can someone explain to me what I'...
by Wilson Yeh 1L
Tue Feb 20, 2018 5:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11 d&e [ENDORSED]
Replies: 1
Views: 156

14.11 d&e [ENDORSED]

Write the half reactions and the balanced equation for the cell reaction for each of the following galvanic cells: d.) Pt(s)|O2(g)|H+(aq)||OH-(aq)|O2(g)|Pt(s) e.) Pt(s)|Sn4+(aq),Sn2+(aq)||Cl-(aq)|Hg2Cl2(s)|Hg(l) How would I go about doing d and e? A through c was pretty straightforward in that on th...
by Wilson Yeh 1L
Tue Feb 13, 2018 7:43 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.101 sign?
Replies: 1
Views: 101

9.101 sign?

A heat pump heats a house in winter by extracting heat from the cold outdoors and releasing it into the warm interior. For the transfer of a given amount of heat, (a) how do the entropies of the interior and exterior of the house change (increase or decrease)? (b) Which change is greater? Assume tha...
by Wilson Yeh 1L
Tue Feb 13, 2018 6:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.99
Replies: 1
Views: 112

11.99

For part A: Calculate the standard Gibbs free energies of formation of the halogen atoms X(g) at 1000. K from data available in Table 11.2.

Why is the standard Gibbs free energies of formation in the answer given in positive values and not negative?
by Wilson Yeh 1L
Tue Feb 13, 2018 5:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.115
Replies: 1
Views: 93

11.115

The overall photosynthesis reaction is 6 CO2(g) + 6 H2O(l) --> C6H12O6(aq) + 6 O2(g). Standard enthalpy of reaction is +2802 kJ. State the equilibrium composition. The answer states for part B and part F that there is no effect when the system is compressed and water is added, respectively. Why is t...
by Wilson Yeh 1L
Mon Feb 12, 2018 7:02 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U = 0
Replies: 2
Views: 149

Delta U = 0

Why does delta U = 0 for an isothermal expansion of an ideal gas?
by Wilson Yeh 1L
Sun Feb 11, 2018 11:53 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp/Cv and molecular structure?
Replies: 1
Views: 102

Cp/Cv and molecular structure?

In section 8.10, it states Cv,m is 3/2 * R for atoms, 5/2 * R for linear molecules, and 3R for nonlinear molecules. Aren't diatomic molecules like oxygen linear? So what would be the rule there for what value to use? I know it should be 3/2 * R but could someone clarify this for me? Thanks!
by Wilson Yeh 1L
Sun Feb 11, 2018 10:55 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp v. Cv!
Replies: 5
Views: 233

Cp v. Cv!

Can someone explain to me when to use Cv and when to use Cp? My TA discussed this in my discussion section but I still don't understand when to use either. Yes, I get that you use Cv under constant volume and you use Cp under constant pressure, but I still don't understand when you would use it. The...
by Wilson Yeh 1L
Sun Feb 11, 2018 10:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Do we ever need to convert pressure?
Replies: 1
Views: 82

Do we ever need to convert pressure?

Is there a standard unit of pressure for the equation \Delta S = nRln\frac{P1}{P2} Like say they give it in atm, kPA, bar, etc. does it matter if I just use those units straight up or do I have to convert it to a standard unit like atm? From the textbook it doesn't seem like I have to, but I'm reall...
by Wilson Yeh 1L
Thu Feb 08, 2018 7:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.81
Replies: 2
Views: 112

11.81

A gaseous mixture consisting of 2.23 mmol N2 and 6.69 mmol H2 in a 500.-mL container was heated to 600. K and allowed to reach equilibrium. Will more ammonia be formed if that equilibrium mixture is then heated to 700. K? For N2(g) + 3 H2(g) <--> 2 NH3(g), K = 1.7 x 10-3 at 600. K and 7.8 x 10-5 at ...
by Wilson Yeh 1L
Thu Feb 08, 2018 6:33 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.17
Replies: 10
Views: 347

Re: 11.17

I also got -2.7 kJ/mol! I spent the past hour trying to figure out what I was doing wrong but it seems like it might just be an error in the solution.
by Wilson Yeh 1L
Thu Feb 08, 2018 5:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.15
Replies: 8
Views: 395

Re: 11.15

Start with the equations \Delta G = \Delta G^{o} + RTlnQ and \Delta G^{o} = -RTlnK Everything is given except Q, which can be calculated using the partial pressures given. The Gibbs free energy of the reaction can then be calculated. Hope this helps! Thanks! I did it but ended up with 8.3 not the a...
by Wilson Yeh 1L
Thu Feb 08, 2018 5:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.15
Replies: 8
Views: 395

11.15

(a) Calculate the reaction Gibbs free energy of I2(g) --> 2I(g) at 1200. K (K = 6.8) when the partial pressures of I2 and I are 0.13 bar and 0.98 bar, respectively. (b) What is the spontaneous direction of the reaction? Explain briefly.

Can someone explain how to approach this? I'm so lost.
by Wilson Yeh 1L
Fri Feb 02, 2018 10:56 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Ideal Situation vs. Real Situation
Replies: 2
Views: 110

Re: Ideal Situation vs. Real Situation

The volume of real gases are greater and harder to compress. Because of this, entropy of real gases are greater than entropy of ideal gases.
by Wilson Yeh 1L
Fri Feb 02, 2018 10:38 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.27
Replies: 1
Views: 130

9.27

Can somebody give me a detailed reasoning for why each answer is what it is? I feel like I have a general idea but I'd like to be sure. Thanks! 9.27 Which substance in each of the following pairs has the higher molar entropy at 298 K: (a) HBr(g) or HF(g); (b) NH3(g) or Ne(g); (c) I2(s) or I2(l); (d)...
by Wilson Yeh 1L
Fri Feb 02, 2018 12:38 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Question about equation?
Replies: 3
Views: 116

Question about equation?

For the equation:
delta(S) from T1 to T2 = n*C*ln(T2/T1)

Where does the C come from? Is that supposed to be heat capacity, and of what exactly? Also, how would I go about solving a problem involving a change in temperature and entropy utilizing this equation if C isn't given? Thanks!
by Wilson Yeh 1L
Fri Jan 26, 2018 12:12 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Changing the energy of a system
Replies: 6
Views: 231

Re: Changing the energy of a system

The energy increases. It's also important to note that energy is required to break bonds within a system and energy is lost when bonds are formed.
by Wilson Yeh 1L
Fri Jan 26, 2018 12:09 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question regarding ice in water?
Replies: 2
Views: 157

Question regarding ice in water?

Usually in questions where say a piece of ice is dropped in water in order to calculate heat flow, energy change, etc. I generally take into account that the ice will melt into water completely and use that energy in order to answer my problem. However, I was wondering how I would know of a situatio...
by Wilson Yeh 1L
Thu Jan 25, 2018 11:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57 question
Replies: 1
Views: 159

8.57 question

Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2(g) + 2 H2(g) --> C2H6(g), from the following data: DeltaHc(C2H2, g) -1300. kJ·mol-1, DeltaHc(C2H6, g) -1560. kJ·mol-1, DeltaH(H2, g) -286 kJ·mol-1. I understand how to do this problem using Hess's Law, the first method. ...
by Wilson Yeh 1L
Fri Jan 19, 2018 12:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45 question
Replies: 4
Views: 131

Re: 8.45 question

The problem asks later on, "How much heat is absorbed in the reaction of 1.25 mol S8 at constant pressure?" showing that the reaction needs energy in the form of heat. Not all chemical reactions are exothermic; some such as this one are endothermic and require energy to take place. I unde...
by Wilson Yeh 1L
Fri Jan 19, 2018 12:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45 question
Replies: 4
Views: 131

8.45 question

In question 8.45 it states that carbon disulfide can be prepared from coke and elemental sulfur:

4C(s)+S8(s) --> 4CS2(l)
delta(H) = +358.8 kJ

My question is I thought that whenever something is being formed it would be exothermic, so in this case why is it positive 358.8 kJ not negative?
by Wilson Yeh 1L
Wed Jan 17, 2018 9:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.19 heating water in a copper kettle
Replies: 3
Views: 156

Re: 8.19 heating water in a copper kettle

I think if the question supplies the specific heat capacity of the container then yes, you would have to account for the specific heat of the container.
by Wilson Yeh 1L
Wed Jan 17, 2018 9:17 pm
Forum: Phase Changes & Related Calculations
Topic: Compression (Question 8.3)
Replies: 4
Views: 128

Re: Compression (Question 8.3)

The answer is positive because when compressing a bike pump you're doing work and increasing the internal energy inside the pump. Basically, the energy is being transferred from you into the air inside the bike pump. As such, the energy is positive. It would be negative if energy was released in the...
by Wilson Yeh 1L
Wed Jan 17, 2018 9:04 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.1 question
Replies: 8
Views: 274

8.1 question

Why is coffee in a thermos bottle considered an isolated system? Why is it not closed? From personal experience the coffee in my thermos bottles would eventually cool down within an hour or so--doesn't that mean energy is being exchanged with the surroundings?
by Wilson Yeh 1L
Thu Jan 11, 2018 7:25 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework Problem 8.19
Replies: 3
Views: 170

Re: Homework Problem 8.19

I did what the above posters did as well and got the same answer. I'm just curious as to why the book answer is 1.4 x 10^2 kJ? Shouldn't it be 1.5 if anything?
by Wilson Yeh 1L
Thu Jan 11, 2018 4:58 pm
Forum: Administrative Questions and Class Announcements
Topic: Can homework be written in pencil?
Replies: 6
Views: 287

Can homework be written in pencil?

I know exams and tests must be written in pen, but just double-checking--are pencils okay for homework problems?
by Wilson Yeh 1L
Wed Jan 10, 2018 10:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Equation for a non-state property?
Replies: 4
Views: 150

Equation for a non-state property?

So I know that a state property is not dependent on path taken, but rather just final - initial. However, for a non-state property like work and heat, what would be the equation to solve for it?
by Wilson Yeh 1L
Wed Jan 10, 2018 9:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question about today's lecture problem?
Replies: 3
Views: 134

Question about today's lecture problem?

In today's lecture there was an example on nitrogen dioxide formation. For method 1, how did the first two reactions add up to form the third reaction? 1. N2 (g) + O2 (g) -> 2NO (g) 2. 2NO (g) + O2 (g) -> 2NO (g) 3. N2 (g) + 2O2(g) -> 2NO2 (g) So my question is how did it get from 1 and 2 to 3?
by Wilson Yeh 1L
Wed Jan 10, 2018 5:17 pm
Forum: Phase Changes & Related Calculations
Topic: Endo and Exothermic Ways to Remember
Replies: 28
Views: 2655

Re: Endo and Exothermic Ways to Remember

On top of what the others have posted, I think it's also very important to come up with a way to remember that endothermic reactions break bonds and exothermic reactions form bonds. For me, I just imagine in my head the game of pool when the cue ball is used to break at the beginning of the game. Th...

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