Search found 19 matches

by Xinjie Su 2J
Sun Mar 13, 2016 1:41 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Substituent Positions on Cyclohexane
Replies: 2
Views: 387

Re: Substituent Positions on Cyclohexane

I think unless it's specified that it's cis structure, substituents should be pointing at opposite directions to reach the most stable state.
by Xinjie Su 2J
Sun Feb 28, 2016 11:52 am
Forum: *Alkanes
Topic: Numbering Cs
Replies: 1
Views: 317

Numbering Cs

In lecture Dr. Lavelle said that we were not supposed to use "sum rule" when numbering carbons. So just to clarify, we should put all substituents in alphabetical order and compare all possible numbering options for each of them until we find the first lower number?
Thanks ^^
by Xinjie Su 2J
Sat Feb 20, 2016 1:18 pm
Forum: *Electrophilic Addition
Topic: Breaking double bonds
Replies: 1
Views: 1403

Breaking double bonds

In Friday's lecture we learned about the reaction between HBr and 2-Butene. In step 1 it is said that one of the C=C double bonds is broken to form a C-H bond. But I thought when breaking C=C double bonds we needed to break both of the bonds to form new ones because the bond energies were different ...
by Xinjie Su 2J
Tue Feb 09, 2016 3:27 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Winter 2014 Midterm Q8
Replies: 3
Views: 716

Re: Winter 2014 Midterm Q8

I also have the same question. I thought when we derive the overall equation for this reaction we would cancel out the coefficients and get HF(aq)---H+(aq) +F-(aq). Why can't we cancel the coefficients out?
by Xinjie Su 2J
Mon Feb 08, 2016 9:58 pm
Forum: Phase Changes & Related Calculations
Topic: Possible scientific errors
Replies: 1
Views: 281

Possible scientific errors

When doing calculations on phase change heat transfer, especially those with multiple steps, I often get answers that are slightly different from what is given on the solution manual. This happens a lot if I do those problems in separate steps. I wonder how much of these errors is considered accepta...
by Xinjie Su 2J
Mon Feb 08, 2016 12:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy change in Volume
Replies: 1
Views: 376

Re: Entropy change in Volume

There are 2 formulas for delta S calculation. One is nRln(V2/V1) for change in volume and constant temperature situations. The other is nCln(T2/T1) for change in temperature situations. Use Cv for when there's constant volume and Cp for constant pressure.
Hope it helps. ^^
by Xinjie Su 2J
Mon Feb 08, 2016 12:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Winter 2011 Midterm Question 2B
Replies: 2
Views: 382

Re: Winter 2011 Midterm Question 2B

For this question, it's not 1mol of monoatomic gas and 1mol of diatomic gas in both containers A &B; it's 1mol of ATOMS in those containers. So it comes out to be 1mol of monoatomic gas in container A and 1/2mols of diatomic gas in container B. So container A contains more particles than contain...
by Xinjie Su 2J
Thu Feb 04, 2016 4:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: standard free energy of reaction
Replies: 1
Views: 501

standard free energy of reaction

In Q4 of winter 2011 midterm, there is the equation PCl3(g)+Cl2(g)--->PCl5(g) at equilibrium and delta G for PCl5 & PCl3 are also given. I understand that I need to figure out the delta G(rxn) to solve this problem but since the reaction is at equilibrium, shouldn't delta G(rxn) be 0? Also, in t...
by Xinjie Su 2J
Sun Jan 31, 2016 11:05 pm
Forum: Balancing Redox Reactions
Topic: standard reaction potentials
Replies: 1
Views: 279

Re: standard reaction potentials

Because standard reaction potential is an intensive property that does not depend on how many times the rxn occurs. So when balancing the equation and multiplying the half reactions, standard rxn potentials stay the same.
Hope it helps ^^
by Xinjie Su 2J
Fri Jan 22, 2016 3:43 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7951
Views: 1215610

Re: Chemistry Jokes

One property of liquid is that it can fit into containers of any shape and automatically takes up all the space.

So...cat is a liquid!!
by Xinjie Su 2J
Sun Jan 17, 2016 9:12 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework 8.11
Replies: 3
Views: 1412

Homework 8.11

Question 8.11: A piston confines 0.200mol Ne(g) in 1.20L at 25C. part (a)The gas is allowed to expand through an additional 1.20L against a constant pressure of 1.00 atm. To calculate the work done in this situation, I apply the w=-PdeltaV equation, but I really don't understand why -(1.00atm)(1.20L...
by Xinjie Su 2J
Sun Jan 17, 2016 8:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: pressure units
Replies: 2
Views: 341

pressure units

In the homework questions I notice they use different units for pressure of gases, sometimes atm, sometimes bar or torr. Are they the same or how do I convert one to another?
by Xinjie Su 2J
Thu Jan 07, 2016 6:07 pm
Forum: Phase Changes & Related Calculations
Topic: Explaining kJ/mol
Replies: 3
Views: 640

Re: Explaining kJ/mol

I think usually we use kJ to describe the the total enthalpy change of a rxn with a chemical equation balanced to its smallest integer coefficients. Take the example of formation of NO2(g) from the course reader, the balanced equation is N2(g)+2O2(g)---->2NO2(g) and the total enthalpy change is 68kJ...
by Xinjie Su 2J
Sun Nov 29, 2015 11:00 pm
Forum: Identifying Acidic & Basic Salts
Topic: Na+ in a reaction
Replies: 2
Views: 2111

Re: Na+ in a reaction

I think because Na+ ions are completely dissolved in water and they remain unchanged throughout the reaction. If you write the chemical equation with Na+ it would be "CH3COO-+H2O+Na+<-->OH-+CH3COOH+Na+". Since the same amount of Na+ appear on both sides of the equation they will cancel eac...
by Xinjie Su 2J
Sun Nov 29, 2015 10:47 pm
Forum: Lewis Structures
Topic: Video: Homework 3.37
Replies: 1
Views: 373

Video: Homework 3.37

This is an explanation of homework problem 3.37 which is about Lewis structure.
And I apologize for the background noise...
by Xinjie Su 2J
Sun Nov 22, 2015 10:31 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Homework Question 12.51 A
Replies: 5
Views: 716

Re: Homework Question 12.51 A

I think first you can consider this problem with atomic radius. That is, since chlorine has a larger atomic radius than fluorine, the H-Cl bond is longer than H-F bond, which means HCl has weaker bonds and is more likely to dissociate in water compared to HF. So HCl is a stronger acid. On the other ...
by Xinjie Su 2J
Wed Nov 11, 2015 1:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework Problem 11.67
Replies: 2
Views: 402

Re: Homework Problem 11.67

I think because the reactants are strongly favored, the reaction to the right can't happen with the original partial pressures. It happens only when one of the products is used up, in this case, H2(g). So we need to calculate the new initial partial pressures in which the reaction to the right stars...
by Xinjie Su 2J
Fri Nov 06, 2015 5:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium and limiting reactant
Replies: 1
Views: 2886

Equilibrium and limiting reactant

As K=[product]/[reactant], my understand is that when a reaction reaches equilibrium, products and reactants are both being formed at a constant rate. So when we say a reaction ends, does it mean the reaction is at equilibrium? If so, since the reactants are not literally "used up", how ca...

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