## Search found 33 matches

Thu Mar 15, 2018 4:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculate standard potential, Gibbs free
Replies: 2
Views: 178

### Calculate standard potential, Gibbs free

On test 2, #7, we have to use Gibbs free energy to calculate the standard potential because standard potentials cannot be added since they are not a state function. However, when it asks to calculate standard cell potential in #6D, we just add -1.24V + 2.04V to get the answer. I dont understand when...
Thu Mar 15, 2018 4:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 #7
Replies: 5
Views: 596

### Re: Test #2 #7

Im confused as to where n(overall)=6. Can you please explain?
Thu Mar 08, 2018 4:52 pm
Forum: Zero Order Reactions
Topic: graph of 0 order
Replies: 10
Views: 800

### Re: graph of 0 order

Go to Dr. Lavelle's page, and under Math Assistance, there is a Kinetic file. There is a detailed graph on page 3.
Thu Mar 08, 2018 4:43 pm
Forum: General Rate Laws
Topic: Rate Constant k
Replies: 6
Views: 417

### Re: Rate Constant k

Also, rate constants are dependent on temperature and activation energy.
Thu Mar 08, 2018 4:40 pm
Forum: Zero Order Reactions
Topic: graph of 0 order
Replies: 10
Views: 800

### Re: graph of 0 order

For rxn rate vs time, the graph will have a horizontal line and then abruptly fall to zero when all the reactants are consumed.
For the integrated zero rate law, it will look similar to the graph of first-order integrated rate law where the slope= -k
Wed Mar 07, 2018 10:57 pm
Forum: First Order Reactions
Topic: 15.29
Replies: 3
Views: 333

### Re: 15.29

For this question, I got a different answer and was wondering if my method is incorrect.

Part A:

rate= 1/3 d[B]/dt= 1/3[0.018 mol L^-1/ 3min]= 0.002mol L^-1 min^-1
first order rate= k[A]
.002mol L^-1 min^-1= k[0.015 mol L^-1]
k= 0.13 min^-1

The textbook answer is k=0.17 min^-1
Sun Mar 04, 2018 7:31 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8039
Views: 1411231

### Re: Post All Chemistry Jokes Here

I don't trust atoms......

I heard they make up everything.
Sun Mar 04, 2018 7:28 pm
Forum: General Rate Laws
Topic: Knowing rate law equations
Replies: 5
Views: 312

### Re: Knowing rate law equations

My TA said that it is a good idea to know, or at least understand the derivations.
Fri Mar 02, 2018 1:04 pm
Forum: Zero Order Reactions
Topic: Units of k [ENDORSED]
Replies: 13
Views: 662

### Re: Units of k[ENDORSED]

I think the units of k is the same units as concentration.
Thu Feb 22, 2018 10:14 am
Forum: Balancing Redox Reactions
Topic: 14.5 part d
Replies: 7
Views: 401

### Re: 14.5 part d

H2O is added to balance the rxn if you have to balance Oxygen, however there are no oxygen present, so you could skip that step and add H+.
Thu Feb 22, 2018 10:09 am
Forum: Balancing Redox Reactions
Topic: HW #14.3 d
Replies: 3
Views: 239

### Re: HW #14.3 d

Does anyone know how to write a cell diagram for this equation?
Thu Feb 22, 2018 10:05 am
Forum: Balancing Redox Reactions
Topic: 14.1 (b)
Replies: 2
Views: 194

### Re: 14.1 (b)

C2H5OH Oxygen is going to have an ON (Oxidation number) of -2 unless its in a peroxide. Hydrogen is going to have an ON of +1 if its with nonmetals. Now we have to solve for Carbon's ON When adding up all of the ON for C2H5OH, it should equal zero. ____/2 (Carbon)+ 6x +1(Hydrogen) + -2(Oxygen)= O Th...
Mon Feb 12, 2018 5:22 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculating final temperature
Replies: 1
Views: 162

### Calculating final temperature

In order to make iced-tea, a 50.0g ice cube at 0.00C is added to 250 ml of tea at 20.0C. What is final temp of the iced tea once it has reached thermal equilibrium. Assume that no heat is transferred to or from the surroundings. The density of water and iced tea is 1.00g/mL over the range of 0-20 C....
Mon Feb 12, 2018 5:15 pm
Forum: Administrative Questions and Class Announcements
Topic: No class on Wednesday?
Replies: 2
Views: 296

### Re: No class on Wednesday?

There is no class but there is a review session from 2-330 if youre interested.
Mon Feb 12, 2018 5:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Practice Midterm Karen Leung #8 [ENDORSED]
Replies: 4
Views: 404

### Re: Practice Midterm Karen Leung #8[ENDORSED]

I figured it out.

Delta S= nCvln(T2/T1)= 3.854mol (5/2R) (ln 326/298)= 4.31

Delta S tot = 22.27 + 4.31= 26.6 J/K
Mon Feb 12, 2018 3:38 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Practice Midterm Karen Leung #8 [ENDORSED]
Replies: 4
Views: 404

### Practice Midterm Karen Leung #8[ENDORSED]

A sealed container has two compartments: one is 7.60 L filled with 83.07g of Ar gas, and the other 5.30L filled with 35.82g of Ne gas a) What is deltaS System if the separating divider is removed and the two gases are allowed to mix? Assume constant temperature at 25 degrees C. I got 22.27J/k b) Wha...
Mon Feb 12, 2018 3:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy sign
Replies: 5
Views: 327

### Re: entropy sign

gas>> liquid >> solid If a rxn has only gas molecules, then you can subtract the number of moles from the product to the reactant. If it is negative, then the change in entropy is negative. If it is positive, then the change in entropy is positive for the forward reaction. example 2CO(g) + O2(g) -->...
Tue Feb 06, 2018 4:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard Gibbs Free Energy of Formation (Units)
Replies: 2
Views: 232

### Standard Gibbs Free Energy of Formation (Units)

When calculating for the standard gibbs free energy of formation, what are the units? Is it Kj or Kj/mole? I thought the answer would be in kilojoules or joules because the moles cancel out when you multiply with n, but the answer in self-test 9.21A has it in kj/mol. In example 9.14, its answer is l...
Tue Feb 06, 2018 4:29 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Example 9.10
Replies: 1
Views: 147

### Re: Example 9.10

Hi, Im not sure if I understood your question clearly but basically, the initial temperature is not 0 degrees C. The T must be converted into Kelvin and so you have to add 273K to the given Celsius to get Kelvin for the temperature.
Mon Feb 05, 2018 10:20 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Reversible vs Irreversible reactions
Replies: 2
Views: 140

### Re: Reversible vs Irreversible reactions

For reversible, you can assume that the total change in entropy should equal to zero. For example, change in entropy for the system could be calculated using nRln(V2/V1). Change in entropy for the surroundings could be calculated by: deltaU=q+w deltaU is equal to zero for an isothermal expansion for...
Mon Feb 05, 2018 10:10 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Reversible vs Irreversible reactions
Replies: 2
Views: 140

### Re: Reversible vs Irreversible reactions

I also had a question regarding reversible vs irreversible reactions.

For chapter 19, Self test 9.17a & b, the question gives us both change in volume and change in pressure, but when solving it why do we only use the change in volume and not the pressure?
Mon Jan 29, 2018 7:37 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Disorder
Replies: 2
Views: 189

### Entropy and Disorder

The textbook uses the "disorder" when defining entropy, but Dr. Lavelle avoids using the term "disorder" in his lectures. Should we try to avoid using this term for future references? For example if the midterm/final were to ask to define entropy. And also, can someone explain en...
Mon Jan 29, 2018 7:14 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Thermodynamics 1st 2nd 3rd Law
Replies: 2
Views: 285

### Thermodynamics 1st 2nd 3rd Law

Can someone explain what the 1st, 2nd, and 3rd law of thermodynamics mean (how they differ)?
Mon Jan 29, 2018 6:55 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Would someone be able to share today's lecture notes please?
Replies: 1
Views: 153

### Re: Would someone be able to share today's lecture notes please?

Sure, I could send you a picture of today's notes if you email me with your phone number. My email address is gracehan0105@gmail.com. I'll try to respond as quickly as possible.
Mon Jan 29, 2018 6:53 pm
Forum: Administrative Questions and Class Announcements
Replies: 3
Views: 300

Hey, my TA advised I do mostly chapter 9 homework problems for homework #3 so I am assuming that this week (HW #4) should be all Chapter 9 problems.
Tue Jan 23, 2018 2:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: H2O as a liquid or vapor
Replies: 2
Views: 112

### Re: H2O as a liquid or vapor

I’m not sure if this is correct, but I think in general, for combustion, Hydrocarbons combust with oxygen to produce carbon dioxide and liquid water.

It would be great if someone could clarify!
Tue Jan 23, 2018 2:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard state
Replies: 2
Views: 131

### Standard state

How do you know if an element or compound is in its standard state? My notes says that while calculating standard rxn enthalpy, to make sure everything is in standard state and if it is not, take into account of phase change.
Tue Jan 23, 2018 2:33 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Material in Book but not in Lectures
Replies: 5
Views: 235

### Re: Material in Book but not in Lectures

I would highly recommend studying the heating and melting curve, and should be able to draw it out to help you visualize the problem regarding phase changes.
Mon Jan 15, 2018 10:43 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: K vs C
Replies: 6
Views: 280

### Re: K vs C

When you are solving for the change in temperature, it does not matter whether you use Kelvin or Celsius because you will get the same answer.
Mon Jan 15, 2018 10:41 pm
Forum: Calculating Work of Expansion
Topic: Ch 8.1 Solving work
Replies: 2
Views: 224

### Ch 8.1 Solving work

In the textbook page 264, there's a self-test problem 8.1A and I keep getting a different answer than the answer provided. Water expands when it freezes. How much work does 100. g of water do when it freezes at and pushes back the metal wall of a pipe that exerts an opposing pressure of 1070 atm? Th...
Fri Jan 12, 2018 3:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Celsius the same as Kelvin? [ENDORSED]
Replies: 9
Views: 2626

### Re: Celsius the same as Kelvin?[ENDORSED]

if you are using the change in temperature, the change is the same whether it is in Kelvin or Celsius,

For example, if Initial temp is 283 K and final temp is 293 K, then change in temp is 10 K.
Now if we change it to Celsius, then initial is 10 C and final is 20 C. The change in temp is 10 C.
Fri Jan 12, 2018 2:55 pm
Forum: Phase Changes & Related Calculations
Topic: Clarification
Replies: 3
Views: 231

### Re: Clarification

I had a similar question and found this link helpful: https://chemistry.stackexchange.com/questions/47150/what-is-the-difference-between-enthalpy-h-and-heat-q It says, "Enthalpy and heat are entirely different things. Enthalpy is a function of state. If you know the state of a system, you know ...
Fri Jan 12, 2018 2:52 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve
Replies: 6
Views: 349

### Re: Heating Curve

I think the length of the heating curve just represents the time it takes to reach a specific temperature.