## Search found 35 matches

Sun Mar 18, 2018 9:43 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Conditions for Maximum Work
Replies: 3
Views: 312

### Conditions for Maximum Work

Why does maximum work of a battery = delta G at constant temperature and pressure? Doesn't maximum work occur for reversible processes, meaning that volume is changing and therefore pressure would not be constant?
Sat Mar 17, 2018 4:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal Energy of Isolated Systems
Replies: 6
Views: 1434

### Re: Internal Energy of Isolated Systems

Thank you so much for all the help!

I was just wondering how having constant internal energy equates to energy being neither created nor destroyed.
Sat Mar 17, 2018 4:33 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal Energy of Isolated Systems
Replies: 6
Views: 1434

### Re: Internal Energy of Isolated Systems

Can you elaborate on that?
Sat Mar 17, 2018 4:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal Energy of Isolated Systems
Replies: 6
Views: 1434

### Internal Energy of Isolated Systems

I read this in the course reader: The energy of an isolated system must remain constant because no matter or heat can be transferred and the system cannot be physically changed ( \Delta V=0). q=0 and w=0 then \Delta U=q+w=0 I just wanted to confirm that the internal energy of all isolated systems is...
Thu Mar 15, 2018 1:38 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Water in Mechanism
Replies: 5
Views: 351

### Re: Water in Mechanism

Solids and liquids are not included when determining the equilibrium constant K. I'm not sure if liquids are included in the rate law though.
Thu Mar 15, 2018 1:36 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which equilibrium equation to use
Replies: 2
Views: 202

### Re: Which equilibrium equation to use

I just wanted to elaborate on Cristina's answer. The concept behind pseudo equilibrium is that having the fast step before the slow step results in a build up of products for the fast step. As a result, the reaction begins to reverse and create reactants, creating a fake equilibrium. As a result, we...
Thu Mar 15, 2018 1:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.29
Replies: 2
Views: 278

### Re: 14.29

Since the species are under standard conditions, we can refer to Appendix 2B for the phases.
Thu Mar 15, 2018 1:27 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Section 15.12
Replies: 1
Views: 188

### Re: Section 15.12

According to the Kinetics outline posted, I think we just need to know the following:

• Explain how the collision model and activated complex model account for the temperature dependence of reactions.
• Interpret or draw a reaction profile.
Thu Mar 15, 2018 1:21 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test #2 Question 8d
Replies: 1
Views: 163

### Test #2 Question 8d

Consider the following unbalanced half-reactions: Ag (s) + I [sup-][/sup] (aq) -> AgI (s) + e - E^{\circ} (anode) = -0.15V AgCl (s) + e - -> Ag (s) + Cl - (aq) E^{\circ} (cathode) = +0.22V Q = 26.8 E^{\circ} = 0.37V What is the value of E?
Thu Mar 15, 2018 1:02 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test #2 Question 5B
Replies: 2
Views: 312

### Test #2 Question 5B

Rank the following in order of increasing reducing power: I 2 , Br 2 , Al I 2 (s) + 2e - -> 2I - E^{\circ } = 0.54V Br 2 (l) +2e - -> 2Br - E^{\circ} = 1.07V Al 3+ (aq) + 3e - -> Al (s) E^{\circ} = -1.66V Correct Answer: Br 2 < I 2 < Al I understand that reducing powe...
Thu Mar 15, 2018 12:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Question from Wednesday's (03/15/18) Lecture
Replies: 2
Views: 199

### Cell Diagram Question from Wednesday's (03/15/18) Lecture

What is wrong with this cell diagram? Ag (s) I AgBr (s) II Br (aq) I Br 2 (g) I understand that the error we determined was that the left side of the cell diagram lacked a combatting electrode (Pt (s) ). However, I remember someone asking about the line separa...
Mon Mar 12, 2018 1:34 pm
Forum: *Aldehydes
Topic: Carbonyl -> Aldehydes and Ketones [ENDORSED]
Replies: 5
Views: 1314

### Carbonyl -> Aldehydes and Ketones[ENDORSED]

I was wondering if aldehydes and ketones are a subgroup of carbonyl?
Fri Mar 09, 2018 9:51 am
Forum: General Rate Laws
Topic: Problem 15.99
Replies: 1
Views: 169

### Problem 15.99

Which of the following plots will be linear? (f) initial rate against [A] for a reaction that is first order in A (g) half-life against [A] for a reaction that is zero order in A (h) half-life against [A] for a reaction that is second order in A I'm not sure how to conceptually or mathematically det...
Fri Feb 23, 2018 9:36 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: ln vs log [ENDORSED]
Replies: 5
Views: 388

### ln vs log[ENDORSED]

I've noticed that sometimes we use log instead of ln in the Nernst equation. I was wondering if there's a reason we would prefer to use log over ln or if there is no difference.
Tue Feb 20, 2018 4:16 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8245
Views: 1440129

### Re: Post All Chemistry Jokes Here

Tue Feb 20, 2018 2:38 pm
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 7
Views: 487

### Re: Oxidation state

Assuming your asking about assigning oxidation numbers, there are a few rules to follow. 1) atoms in their natural state are assigned 0 (e.g., Al, H 2 ) 2) monatomic ions are assigned their charge (e.g., Na + = +1) 3) neutral compounds are assigned 0 (e.g., CO 2 ) 4) polyatomic ions are assigned the...
Wed Feb 14, 2018 12:25 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework 9.19 [ENDORSED]
Replies: 5
Views: 791

### Re: Homework 9.19[ENDORSED]

This problem wants you to find the standard entropy of vaporization of water at 85 C reversibly. This takes much more work by the system than an irreversible vaporization of water at 85 C, which consists of one step and lots of energy lost as heat. To do it reversibly: 1.) reversibly heat the water...
Tue Feb 13, 2018 1:59 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: K_b
Replies: 2
Views: 224

### Re: K_b

As explained above k b is the Boltzmann constant and does equal to R/Avogadro's number. It's applied in the Boltzmann equation S = k b lnW. This equation calculates the entropy of ideal gases in relation to their degeneracy W, the number of microstates of the molecule (so basically the number of pos...
Tue Feb 13, 2018 1:45 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal system [ENDORSED]
Replies: 3
Views: 341

### Re: isothermal system[ENDORSED]

Isothermal means temperature does not change and therefore internal energy does not change. Delta U = q + w 0 = q + w Therefore -q = w Or w = -q Heat is transferred (not zero) but the same amount of energy is lost as work. Therefore internal energy is constant. If needed, ask during my Monday revie...
Tue Feb 13, 2018 1:42 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible but not-isothermal expansion?
Replies: 3
Views: 276

### Re: Reversible but not-isothermal expansion?

Same. It seems like every problem referring to a reversible system also mentions that the system is isothermal. I was wondering if the fact that the system is isothermal makes it reversible, but that correlation doesn't seem to conceptually or mathematically add up for me.
Tue Feb 13, 2018 1:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Irreversible vs Reversible
Replies: 3
Views: 279

### Re: Irreversible vs Reversible

Mitch Mologne 1A wrote:If the pressure is constant, you known the process is irreversible.

How would you know if a process is reversible though?
Tue Feb 13, 2018 12:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy (W) [ENDORSED]
Replies: 1
Views: 178

### Degeneracy (W)[ENDORSED]

Why is W at its max when isolated systems are at equilibrium? And what does it mean for W to be at its max? It kind of sounds like there's a range of possible values for W and I thought there was just one set value calculated by W=2^n.
Tue Feb 13, 2018 12:48 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann Equation
Replies: 2
Views: 162

### Re: Boltzmann Equation

It is important to specifically note that because when dealing with actual, complex molecules, it is difficult to know the exact number of microstates, W. It is often the case that we do not know the exact number of microstates, but that is okay because if we can estimate it, then we will still obt...
Tue Feb 13, 2018 12:42 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann Equation
Replies: 2
Views: 162

### Boltzmann Equation

I was reviewing the course reader and noticed that under the Boltzmann equation, S = k lnW, it's noted that a large error in W would result in a small error in S. I can see mathematically how that would work out. I just don't understand why it's important to specifically note that?

Thanks!
Mon Feb 05, 2018 12:57 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: test question 7 [ENDORSED]
Replies: 6
Views: 429

### Re: test question 7[ENDORSED]

Yes, Delta H (fusion) for water was given. We were supposed to treat the tea as if it was just water.
Mon Feb 05, 2018 12:54 pm
Forum: Calculating Work of Expansion
Topic: Midterm [ENDORSED]
Replies: 3
Views: 290

### Re: Midterm[ENDORSED]

I think we will have access to the same equations sheets during our midterm. Most of the basic equations we need are listed on there. Some of the equations he derived in class aren't listed, but it should still be possible to solve problems without those derived equations. The derived equations just...
Mon Feb 05, 2018 12:51 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: test question 5
Replies: 5
Views: 380

### Re: test question 5

So in this question, is the system considered the contents of the cooler as well as the cooler itself, rather than just the contents being the system? In this question, the contents of the cooler alone should be considered the system. The cooler itself should be considered the surrounding. Since th...
Mon Jan 22, 2018 3:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Concepts for Chapter 8 [ENDORSED]
Replies: 5
Views: 387

### Re: Concepts for Chapter 8[ENDORSED]

I've found that making flashcards based off lecture notes is enough for me to understand and apply the concepts.
Sat Jan 20, 2018 9:38 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q(sys) = -q(surr)
Replies: 3
Views: 892

### q(sys) = -q(surr)

I understand why q(sys) + q(surr) = 0.

I was wondering how we can determine if we use

-q(sys) = q(surr)

or

q(sys) = -q(surr)
Sat Jan 20, 2018 9:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capcity for Water
Replies: 8
Views: 343

### Re: Heat Capcity for Water

Yes, the heat capacity should always be given. I don't think we have the means to calculate heat capacity outside of a lab setting.
Sat Jan 20, 2018 9:17 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding change in enthalpy when given bond enthalpies
Replies: 3
Views: 187

### Re: Finding change in enthalpy when given bond enthalpies

Yes, you can subtract all of the reactants from all of the products and still get the correct answer. Technically however the enthalpy of the reaction is the net of the energy released from forming bonds and the energy absorbed from breaking bonds.
Wed Jan 10, 2018 11:49 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy of Freezing
Replies: 4
Views: 516

### Re: Enthalpy of Freezing

Sorry if I'm totally off, but wouldn't the negative sign be required and not arbitrary in this case. I believe freezing is the reverse reaction of melting/fusion. Since melting/fusion is endothermic and therefore has a positive enthalpy value, wouldn't freezing be exothermic and therefore have a neg...
Wed Jan 10, 2018 11:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 6
Views: 412

### Re: Bond Enthalpies

OH WOW YOU GUYS TYPE FAST.
Wed Jan 10, 2018 11:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 6
Views: 412

### Re: Bond Enthalpies

Can someone please explain to me why bond enthalpies (method 2) are always positive? Thank you! Yea np I gotchu girl! In method 2, the bond enthalpy values given are always positive, because the value given represents the amount of kJ/mol required to break the bond. Since breaking the bond requires...
Wed Jan 10, 2018 11:21 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8245
Views: 1440129

### Re: Post All Chemistry Jokes Here

what did the ice cube say to his mom as he was melting