Search found 27 matches

by Courtnie Ly
Sat Mar 12, 2016 8:19 am
Forum: *Alcohols
Topic: 2013 Final 5B, page 206
Replies: 2
Views: 506

Re: 2013 Final 5B, page 206

Ahh ok makes sense, thank you!
by Courtnie Ly
Fri Mar 11, 2016 10:30 pm
Forum: *Alcohols
Topic: 2013 Final 5B, page 206
Replies: 2
Views: 506

2013 Final 5B, page 206

I got the name 2-iodobut-2-en-1-ol, but could someone explain to me why it's (Z)-2-iodobut-2-en-1-ol?
by Courtnie Ly
Sat Mar 05, 2016 10:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Winter 2011 Final Q1A
Replies: 1
Views: 386

Winter 2011 Final Q1A

"Suppose you want to use methane gas to boil 50 mL of water at 25ºC. How many grams of methane gas would need to be combusted to generate the required heat?" I understand that q=mCdT is the equation used to solve this problem, but the solution plugs in 50 g for the m of water. How did they...
by Courtnie Ly
Sun Feb 28, 2016 9:56 pm
Forum: *Alkenes
Topic: Homework 1.12C naming
Replies: 2
Views: 466

Re: Homework 1.12C naming

I got the same answer that you did, perhaps it's because you want to get the lowest number possible for the pentene? (2 instead of 3)
by Courtnie Ly
Sun Feb 21, 2016 9:24 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetically Controlled vs. Thermodynamically Controlled
Replies: 3
Views: 740

Re: Kinetically Controlled vs. Thermodynamically Controlled

"Thermodynamic analysis tells us if forward or reverse process is favored (does not say how fast)...kinetic analysis: speed or rate of reaction" (page 59 of course reader). I think that the main difference is that thermodynamics deals with state functions (enthalpy, entropy, free energy), ...
by Courtnie Ly
Sat Feb 13, 2016 9:43 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Formal definiton of the rate constant?
Replies: 1
Views: 387

Re: Formal definiton of the rate constant?

"In chemical kinetics a reaction rate constant or reaction rate coefficient, k, quantifies the rate of a chemical reaction. For a reaction between reactants A and B to form product C." (Found this on google) But I think if we think back to 14a when we did equilibrium, the rate constant is ...
by Courtnie Ly
Sun Feb 07, 2016 7:58 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Winter 2011 Midterm Question 3
Replies: 1
Views: 376

Winter 2011 Midterm Question 3

For this problem, the solution uses 2.78 moles and 3.61 moles. When I did it, I didn't round and I used 3.6079 moles and 2.7753 moles. The solution gets the final temperature to be 310.1 K and I got 309.96 K. I ended up getting a different answer (0.57 J/K rather than 0.8 J/K) than the solution and ...
by Courtnie Ly
Sat Feb 06, 2016 10:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Friday Quiz Question #4
Replies: 2
Views: 446

Friday Quiz Question #4

"NASA has recently considered the use of steam-powered rockets on an efficient, but very slow, journey to Mars. Solar panels are to heat the water into steam to be later ejected from the nozzle of the rocket. Assuming that the temperature inside the engine is 100ºC and the temperature of space ...
by Courtnie Ly
Fri Jan 29, 2016 9:07 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Workbook p. 14 #11
Replies: 4
Views: 549

Re: Workbook p. 14 #11

Hi can you post the question in full so that we can help you? A system undergoes a two-step process. In step 1, it expands adiabatically from 1.00L to 2.56 L at 1.00 atm (external pressure). In step 2, it releases 73 J of heat at 1.00 atm as it returns to the original internal energy. Find the fina...
by Courtnie Ly
Fri Jan 29, 2016 9:02 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Workbook p. 14 #11
Replies: 4
Views: 549

Re: Workbook p. 14 #11

A system undergoes a two-step process. In step 1, it expands adiabatically from 1.00L to 2.56 L at 1.00 atm (external pressure). In step 2, it releases 73 J of heat at 1.00 atm as it returns to the original internal energy. Find the final volume of the system. For part 1 I did w = -PdV and got -158 ...
by Courtnie Ly
Thu Jan 28, 2016 10:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Workbook p. 14 #11
Replies: 4
Views: 549

Workbook p. 14 #11

I did part 1 of this question correctly (I got w = -158 J).
I understand that it's adiabatic, so q = 0, and delta U = q + w so delta U = w. Thus, wouldn't delta U = -158 J as well? The solution for part II sets delta U equal to +158 J rather than negative. Why is that?
by Courtnie Ly
Thu Jan 28, 2016 9:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: bond enthalpies
Replies: 1
Views: 264

Re: bond enthalpies

When you break a bond, you must put energy into the bond to break it (energy/heat is a reactant-->endothermic reaction, therefore enthalpy is positive). On the other hand, when you form a bond, energy is released, so it's exothermic (negative dH).
by Courtnie Ly
Wed Jan 20, 2016 11:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework 9.13
Replies: 1
Views: 361

Homework 9.13

I saw that there was a typo for this problem in the solutions manual, but I still have a question about it. The corrected answer states that:
∆S = (n)(Cv)(R)(ln T1/T2), where Cv = (5/2)(R)

However, I was wondering, why do we use Cv instead of Cp? Isn't the volume changing?
by Courtnie Ly
Mon Jan 18, 2016 1:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework 8.65
Replies: 1
Views: 899

Homework 8.65

The question asks for the standard enthalpy of formation of dinitrogen pentoxide, given: 2 NO (g) + O2 (g) ---> 2 NO2 (g) (dH = -114.1 kJ) 4 NO2 (g) + O2 (g) ---> 2 N2O5 (g) (dH = -110.2 kJ) The solutions manual states that the reaction we want is: N2 (g) + 5/2 O2 (g) ---> N205 (g) Can somebody expl...
by Courtnie Ly
Mon Jan 18, 2016 1:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.62 (Hess' Law)
Replies: 4
Views: 525

Re: Question 8.62 (Hess' Law)

I got a different answer. Why do we multiply the second equation by 6?
by Courtnie Ly
Mon Jan 11, 2016 7:49 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.19 part a
Replies: 3
Views: 394

Re: 8.19 part a

Krish Seth 2L wrote:Cs is a constant


Is it different for each system or is it always the same constant?
by Courtnie Ly
Fri Jan 08, 2016 11:20 am
Forum: Phase Changes & Related Calculations
Topic: Steam burn
Replies: 3
Views: 629

Re: Steam burn

Yes, I believe it's because although they are the same temperature, the steam has more heat because of the heat/energy supplied during the boiling process (phase transition, page 17 of the course reader).
by Courtnie Ly
Sat Dec 05, 2015 5:08 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Homework 13.21d
Replies: 1
Views: 570

Homework 13.21d

"What volume of 0.200 m K2CO3(aq) must be added to 100. mL of 0.100 m KHCO3(aq) to prepare a buffer solution with a pH of 11.0?"

I solved for the moles of HCO3- and got 0.01 moles but I don't know where to go from there. Why are 5.6x10-2 moles of K2CO3 required to get a pH of 11?
by Courtnie Ly
Sun Nov 29, 2015 10:52 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Dilution of Aqueous Solutions
Replies: 1
Views: 392

Dilution of Aqueous Solutions

When calculating the pH/pOH of a diluted aqueous solution, why do you divide the original volume by the final volume? Ex. Homework 12.29d asks to solve for the pH/pOH of 2.00 mL of 0.175 m KOH(aq) after dilution to 0.500 L. The solutions manual solves this by calculating the [OH-] by multiplying the...
by Courtnie Ly
Sun Nov 29, 2015 6:39 pm
Forum: Identifying Acidic & Basic Salts
Topic: Anions as Acids
Replies: 1
Views: 382

Anions as Acids

The course reader says that very few anions act as acids because it is more difficult for an anion to lose H+. Why are HSO4- and H2PO4- exceptions to this rule?
by Courtnie Ly
Fri Nov 20, 2015 4:52 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: How to calculate the equilibrium for carbonic acid?
Replies: 1
Views: 915

Re: How to calculate the equilibrium for carbonic acid?

If you refer to page 146 of the course reader it shows the reaction:

H2CO3 + H2O <-> HCO3- + H3O+
Ka1= [H3O+][HCO3-]/[H2CO3]

HCO3- + H2O <-> CO32- + H3O+
Ka2 = [H3O+][CO32-]/[HCO3-]

K(overall) = Ka1Ka2 = [H3O+][HCO3-][H3O+][CO32-]/[H2CO3][HCO3-]
= [H3O+]^2[CO32-]/[H2CO3]
by Courtnie Ly
Fri Nov 13, 2015 11:59 pm
Forum: Naming
Topic: Homework 17.31c and d
Replies: 1
Views: 266

Homework 17.31c and d

Question 17.31c and d ask you to write the formula for tetraamminediaquacobalt(III) bromide and sodium bisoxalato(diaqua)ferrate(III). 1. When we do these kinds of problems, aren't we supposed to write them in alphabetical order? So for d, why does (C2O4) come after (OH2)? 2. For part c, why does it...
by Courtnie Ly
Sat Nov 07, 2015 12:58 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 11.7c
Replies: 1
Views: 367

Homework 11.7c

c) Assuming that the initial pressure of X2 was 0.10 bar, calculate the value of K for the decomposition. When calculating K, only given the initial pressure of X2, why can you use the molar ratio to find the pressure of the products as well? Is it because pressure remains constant throughout the sy...
by Courtnie Ly
Sat Oct 31, 2015 1:32 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbital Theory
Replies: 1
Views: 325

Molecular Orbital Theory

Why is sigma 2pz higher energy than the pi 2px and 2py in the molecular orbital of charge less than 7 but lower in molecular orbitals with charge greater than 8?
by Courtnie Ly
Fri Oct 23, 2015 9:15 am
Forum: Lewis Structures
Topic: Homework 3.57b
Replies: 1
Views: 373

Homework 3.57b

For 3.57b, it asks for the lewis structure of a hydrogen sulfite ion (HSO3-). I have mine set up with sulfur as the central atom and 3 oxygens and a lone pair around it, and the sulfur is double bonded to one of the oxygens. Then, I also have the hydrogen bonded to the oxygen that is double bonded t...
by Courtnie Ly
Sat Oct 17, 2015 9:18 am
Forum: Ionic & Covalent Bonds
Topic: Bond Strength
Replies: 2
Views: 484

Bond Strength

On page 93 of the textbook, it says "On a plot of the potential energy of a diatomic molecule as a function of the internuclear distance, the dissociation energy is the distance between the bottom of the energy well and the energy of the separated atoms...A high dissociation energy indicates a ...
by Courtnie Ly
Fri Oct 09, 2015 4:59 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Homework 1.43
Replies: 4
Views: 687

Re: Homework 1.43

First, you have to convert 350 pm to m (350 x 10^-12 m = 3.50 x 10^-10 m). Then, use the indeterminacy equation (∆p ∆x ≥ h/4π). ∆p = momentum (mass x velocity) ∆x = position (3.50 x 10^-10 m) mass (of electron) = 9.109 x 10^-31 kg ∆p ∆x ≥ [6.626 x 10^-34 Js/(4 x 3.14)] ∆p ∆x ≥ 5.27 x 10^-35 kg m^2 s...

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