## Search found 18 matches

Sat Mar 18, 2017 11:45 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Winter 2013 final Q4B
Replies: 3
Views: 475
Can someone explain how to find the change in the concentrations of O2 for each droplet after 100s? The equations the solutions has don't make conceptual sense to me. If you look at the original equation 2Fe(s)+ 2H2O(l) + O2(aq) ---> 2Fe(OH)2(s), you'll know how to write Q because Q = [products]/[r...
Thu Mar 16, 2017 1:40 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy at equilibrium pt2
Replies: 2
Views: 329

### Re: Entropy at equilibrium pt2

According to the second law of thermodynamics, the entropy of an isolated system increases in the course of any spontaneous change. The entropy of an "isolated" system reaches a maximum at equilibrium. The system stays there because any further change would reduce entropy. Maximum entropy ...
Sat Mar 11, 2017 7:45 pm
Forum: *Cycloalkenes
Topic: 1.21 a b and c
Replies: 3
Views: 865

### Re: 1.21 a b and c

For part C, is it acceptable to start numbering at the top left before the double bond? It gives nearly the same answer, and since the priority for lower numbers is for the double bonds I would think that the locations of the methyl groups would not matter. The name I got was 3-isopropyl-4,5 dimeth...
Sun Mar 05, 2017 10:02 am
Forum: *Alkanes
Topic: Common vs IUPAC naming
Replies: 3
Views: 391

### Re: Common vs IUPAC naming

*However, after flipping through the practice final exams in the back, I noticed that the Winter 2013 FInal Exam question 6B asked "Write the common name and IUPAC name next to each structure."
Sun Mar 05, 2017 10:00 am
Forum: *Alkanes
Topic: Common vs IUPAC naming
Replies: 3
Views: 391

### Re: Common vs IUPAC naming

I believe Professor Lavelle said in lecture that we only need to know IUPAC. The question may ask: "Give the IUPAC name" or "Give the name of this molecule" in which you can provide either the common name or IUPAC. Common names often make the name of the organic molecules simpler.
Sun Feb 26, 2017 5:28 pm
Forum: Administrative Questions and Class Announcements
Topic: 2/24/17 Bruincast
Replies: 19
Views: 2475

### Re: 2/24/17 Bruincast

Lecture 2's audio is correct for 2/24/17.
Sun Feb 26, 2017 5:21 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: signs
Replies: 6
Views: 720

### Re: signs

We only want to deal with positive rates, therefore when calculating rates we use:
R --> P
(instantaneous) RATE = -d[R]/dt = d[P]/dt
Sat Feb 18, 2017 11:51 pm
Forum: General Rate Laws
Topic: Quiz 2 preparation #2
Replies: 2
Views: 342

### Re: Quiz 2 preparation #2

Reaction rate is defined as the change in concentration of one of the reactants or products divided by the time interval over which the change takes place. For example, R --> P Rate = -d[R]/dt = d[P]/dt The constant k is called the rate constant for the reaction and is dependent on the reaction and ...
Sun Feb 12, 2017 11:00 pm
Forum: Balancing Redox Reactions
Topic: Acidic vs. Basic Solutions
Replies: 2
Views: 328

### Re: Acidic vs. Basic Solutions

In acidic solution, balance O by using H2O and then balance H by using H+.

In basic solution, balance O by using H2O and balance with OH-.
Sun Feb 12, 2017 9:04 pm
Forum: Balancing Redox Reactions
Topic: Review from 14a
Replies: 2
Views: 309

### Re: Review from 14a

Reaction quotient Q = [P]/[R]
More specifically, aA + bB ⇌ cC + dD
Q = [C]^c[D]^d/[A]^a[B]^b

For example, N2(g) + 3H2(aq) ⇌ 2NH3(g)
Q = [NH3(g)]^2/[N2(g)][H2(aq)]^3

Equilibrium constant K is the same format but at equilibrium concentrations.
Sat Feb 11, 2017 1:02 am
Forum: Balancing Redox Reactions
Topic: has anyone tried 14.4.b?
Replies: 1
Views: 367

### Re: has anyone tried 14.4.b?

14.4b C3H7OH + [Cr2O7]2- ---> Cr3+ + C3H6O If the oxidation number increases, then the element is part of the oxidation (loss of electrons) half reaction. Split the equation into the two half reactions: [Cr2O7]2- ---> Cr3+ C3H7OH ---> C3H6O Balance the two half reactions. Since the problem states th...
Sat Feb 04, 2017 11:55 am
Forum: Balancing Redox Reactions
Topic: Ecell properties
Replies: 2
Views: 1061

### Re: Ecell properties

Standard reduction potential is an intensive property because it does not depend on how many times the reaction occurs. Extensive properties (such as mass, volume, entropy, enthalpy, energy, etc.) will not affect the cell POTENTIAL. [A common example Dr. Lavelle used in lecture was water density. No...
Tue Jan 24, 2017 4:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Quiz 1 Prep Question 3
Replies: 1
Views: 324

### Re: Quiz 1 Prep Question 3

Because this is an isothermal reversible reaction, temperature remains constant: ΔT = 0. In an isothermal process (if the gas is ideal), internal energy does not change because the amount of energy entering the surroundings is equal to the amount entering the system. Therefore ΔE = 0. So from the eq...
Tue Jan 24, 2017 3:45 pm
Forum: Phase Changes & Related Calculations
Topic: Quiz prep 1 question 6
Replies: 1
Views: 271

### Re: Quiz prep 1 question 6

The standard enthalpy of combustion of propane (at 298K) is -2220 kJ/mol. That means 1 mole of propane burned releases 2220 kJ of heat. First, find the number of moles of propane that must be burned to release 2580 kJ of heat, using the ratio 2220 kJ/1 mole. After finding the number of moles, you ca...
Tue Jan 24, 2017 3:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpy of formation for ethyne
Replies: 2
Views: 12343

### Re: Standard enthalpy of formation for ethyne

The question does not state that there is a combustion reaction. I think you need to write the equation so that ethyne is the product. Try: 2C(s) + H2(g) --> C2H2(g).

The most stable form of carbon is graphite (solid), and hydrogen is H2 gas.
Fri Jan 20, 2017 6:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51 Sig Figs, Sign [ENDORSED]
Replies: 3
Views: 441

### Re: 8.51 Sig Figs, Sign[ENDORSED]

When enthalpy is negative it just means heat is released from the reaction. Since the question asks for the enthalpy density (enthalpy released per liter), you would simply put the positive number. It would be unconventional to say negative 23.9 x 10^3 kJ/L released (aka negative heat released ???).
Fri Jan 20, 2017 5:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51 Sig Figs, Sign [ENDORSED]
Replies: 3
Views: 441

### Re: 8.51 Sig Figs, Sign[ENDORSED]

The "-67 kJ/mol" value is used in addition/subtraction, in which the answer is rounded to the same precision as the least precise number. Here, the least precise number is to the left of the decimal point (a whole number). That's why the answer is -13168 kJ/mol. Then in multiplication/divi...
Fri Jan 20, 2017 5:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Problem 8.37 [ENDORSED]
Replies: 1
Views: 255

### Re: Problem 8.37[ENDORSED]

I believe it's because you assume the question is asking for the (molar) heat of vaporization, in which the units are always kilojoules per mole.