Search found 34 matches

by Christina Chang 1C
Sun Mar 17, 2019 12:11 am
Forum: General Science Questions
Topic: sig figs
Replies: 4
Views: 243

sig figs

When you calculate delta G with the equation delta G=-nFE and you use the numbers n=2 and E=2.05 V, would the answer be in 1 sig fig or 3 because 2 may be inexact?
by Christina Chang 1C
Wed Mar 13, 2019 11:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Thermodynamics learning outcome
Replies: 1
Views: 146

Thermodynamics learning outcome

Show how ∆S is related to ∆H for a change at constant temperature and pressure and explain the relationship.

Is this learning outcome asking about the equation for the entropy of phase changes where deltaS=deltaH(fusion)/T or is it asking about gibbs free energy.
by Christina Chang 1C
Tue Mar 12, 2019 12:02 am
Forum: Second Order Reactions
Topic: Homework, 6th edition, 15.35
Replies: 3
Views: 76

Re: Homework, 6th edition, 15.35

You are given the [A]0 and you have k, from solving the half-life equation. You are trying to find time and you actually are given [A] as well. For example, in part a) you want to find how long it takes to decrease to one-sixteenth of the original which is [A] and you can figure that out by multiply...
by Christina Chang 1C
Mon Mar 11, 2019 11:58 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 3
Views: 60

Re: Intermediates

The intermediates are the ones that cancel out when you are given multiple steps when finding the overall reaction. I'm not sure if that answered your question.
by Christina Chang 1C
Mon Mar 11, 2019 11:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K
Replies: 1
Views: 38

K

If a question says to write the equilibrium expression K does it matter if its Kc vs Kp because it is not specified?
by Christina Chang 1C
Sat Mar 09, 2019 11:44 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Fast Step vs Slow Step
Replies: 3
Views: 66

Re: Fast Step vs Slow Step

The main difference between the two is that one occurs faster than the other and the slow step determines the rate of the overall reaction because even if the other steps are fast you must depend on the slowest step since it affects the others if that makes sense. As for how you can tell them apart ...
by Christina Chang 1C
Sat Mar 09, 2019 11:38 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Microscopic reversibility
Replies: 4
Views: 69

Re: Microscopic reversibility

Microscopic reversibility is the assumption that a reaction has intermediates in the forward and the reverse direction. Reaction mechanisms are the number of steps to form the products so I'm guessing that in relation to microscopic reversibility, that would mean that the reaction mechanism would be...
by Christina Chang 1C
Sat Mar 09, 2019 11:34 am
Forum: Zero Order Reactions
Topic: Half Life and k
Replies: 11
Views: 304

Re: Half Life and k

I think this is because the half-life equation is derived from the rate law and therefore if you solve for t1/2, k becomes inversely proportional to t1/2.
by Christina Chang 1C
Tue Feb 26, 2019 1:16 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Change in enthalpy
Replies: 2
Views: 54

Re: Change in enthalpy

Endothermic would not be favorable because positive entropy is favorable (since more disorder is generally created) and as a result, if you want free energy to be negative and entropy is positive, enthalpy would have to be negative at a high temperature to guarantee a spontaneous reaction (negative ...
by Christina Chang 1C
Tue Feb 26, 2019 1:07 am
Forum: Balancing Redox Reactions
Topic: Adding H+, OH- and H20
Replies: 4
Views: 106

Re: Adding H+, OH- and H20

For a reaction in acidic solution, when there are unbalanced oxygens you would add H2O and then to balance out the extra hydrogens you would add H+. I'm not sure if that answered your question?
by Christina Chang 1C
Tue Feb 26, 2019 1:04 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt(s) in cell diagram
Replies: 4
Views: 68

Re: Pt(s) in cell diagram

I was confused about that too, but I came to the conclusion that since iodine is not actually a metal then iodine in solid form would not really be fit to be a conductor.
by Christina Chang 1C
Sat Feb 23, 2019 4:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using reverse reactions (Problem 14.11)
Replies: 1
Views: 49

Re: Using reverse reactions (Problem 14.11)

It did not become negative because the H+ reaction was the one that was flipped and the cell potential for that is 0 and 0 cannot be negative. Also, we are able to flip it because you want to cancel out the electrons on both sides.
by Christina Chang 1C
Sat Feb 23, 2019 4:21 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes
Replies: 3
Views: 65

Re: Phase Changes

For just a phase change it would be the moles of substance times the delta heat of fusion for that substance. If there is heat involved then you would also have to account for that too with q=mCdeltaT.
by Christina Chang 1C
Sat Feb 23, 2019 4:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units
Replies: 4
Views: 54

Re: Units

Since Gibbs is energy, I would think that it would be in either joules or kilojoules.
by Christina Chang 1C
Tue Feb 12, 2019 7:05 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: When is delta S = 0?
Replies: 3
Views: 579

Re: When is delta S = 0?

In a review session, one of the TA's said that if the process is reversible then delta S(universe) would be 0, which means that delta S(surroundings)= -delta S(system). Hope that helped!
by Christina Chang 1C
Tue Feb 12, 2019 6:58 pm
Forum: Phase Changes & Related Calculations
Topic: Slope of heating curve
Replies: 8
Views: 303

Re: Slope of heating curve

I think that in general, the high specifc heat would mean that it would be harder to change the temperature of that substance and so the slope would be not as steep as something that would be easier.
by Christina Chang 1C
Tue Feb 12, 2019 6:49 pm
Forum: Phase Changes & Related Calculations
Topic: 6th edition 9.19
Replies: 2
Views: 67

6th edition 9.19

I was not sure how to do this problem, but the solutions guide said to calculate the heat and the phase change and then to calculate the heat of going back too. Why would you have to go back after the phase change?
by Christina Chang 1C
Fri Feb 08, 2019 12:41 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy
Replies: 5
Views: 96

Gibbs free energy

I know that it won’t be on the midterm, but what else does calculating Gibbs free energy tell us besides whether or not the reaction is spontaneous?
by Christina Chang 1C
Fri Feb 08, 2019 12:33 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Enthalpy and Hheat
Replies: 2
Views: 62

Re: Enthalpy and Hheat

I think that delta H =q when the reaction is ran under constant pressure. Hope that helps!
by Christina Chang 1C
Fri Feb 08, 2019 12:27 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: How to know which gas constant to use
Replies: 2
Views: 58

Re: How to know which gas constant to use

It will depends on what other variable units that you have in the equation along with what variable unit you are solving for.
by Christina Chang 1C
Sun Feb 03, 2019 2:16 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: kJ v. kJ/mol
Replies: 3
Views: 57

Re: kJ v. kJ/mol

I'm not sure if this is correct but I think that you would use kJ/mol when it is for the individual molecules and just kJ if it is the total enthalpy for the equation. I hope this helped!
by Christina Chang 1C
Mon Jan 28, 2019 11:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When to use which method for calculating reaction enthalpies
Replies: 4
Views: 64

Re: When to use which method for calculating reaction enthalpies

Do you know which equation to use for question 8.9 in the 6th edition textbook? I'm not sure which equation uses those variables.
by Christina Chang 1C
Mon Jan 28, 2019 9:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: qp
Replies: 3
Views: 43

Re: qp

For number 8.3 in the 6th edition it asks for how much work is done. I'm not sure if we went over in class and if we did does anyone know the equation for work?
by Christina Chang 1C
Sat Jan 26, 2019 10:55 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ICE Box Ratios
Replies: 8
Views: 269

Re: ICE Box Ratios

I'm not sure if this answers your question but if you mean ratios as in using the balanced equations then if the reaction is like A+B-->2C then on the products side of the ice table on the change line it would be -X and -X but for the products side it would be +2X. Hope that helped
by Christina Chang 1C
Tue Jan 22, 2019 10:31 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Increasing the pressure (decreasing volume)
Replies: 2
Views: 50

Re: Increasing the pressure (decreasing volume)

Since pressure would be increased I think you would just double the concentrations to account for the halved volume.
by Christina Chang 1C
Mon Jan 21, 2019 10:57 pm
Forum: Phase Changes & Related Calculations
Topic: How to tell acids and bases
Replies: 8
Views: 163

Re: How to tell acids and bases

Generally, if there is an H it's an acid and if there is an OH then it's a base. I'm not quite sure if that's what you were trying to ask?
by Christina Chang 1C
Mon Jan 21, 2019 10:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Stability
Replies: 3
Views: 51

Re: Stability

If K is larger then it would be less stable because more product is made which means that the original product was not that stable. Hope that helps!
by Christina Chang 1C
Mon Jan 21, 2019 10:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 12.39
Replies: 2
Views: 55

Re: 12.39

HNO2 and HClO2 should be on there but for NH3OH+ it's NH2OH and for (CH3)2NH2+ it's (CH3)2NH because of the +1 charge that the bases have in the question.
by Christina Chang 1C
Mon Jan 14, 2019 11:50 pm
Forum: General Science Questions
Topic: Autoprotolysis
Replies: 3
Views: 255

Re: Autoprotolysis

Autoprotolysis is basically a proton transfer between the same type of molecule. An example of a reaction that is autoprotolysis is 2H20 (l) ---> H30+ (aq) + OH- (aq). There is also suppose to be a reverse reaction arrow but I didn't know how to type it out haha. Hoped this helped!
by Christina Chang 1C
Mon Jan 14, 2019 11:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.77/11.87 6th Edition
Replies: 1
Views: 30

Re: 11.77/11.87 6th Edition

Since it requires energy to break the X-X bond, the reaction is considered to be endothermic. Hope that helps!
by Christina Chang 1C
Mon Jan 14, 2019 11:40 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Volume and Pressure
Replies: 2
Views: 41

Re: Volume and Pressure

If the pressure is increased (volume decreases by compression) then the there is less space essentially and it would prefer the side that has less moles of gas because it won't be as "crowded". That's how I visualize it and I hope it makes sense.
by Christina Chang 1C
Mon Jan 14, 2019 11:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acids and Bases
Replies: 7
Views: 124

Re: Acids and Bases

From looking at a reaction, if it dissociates fully and forms a salt and water then that would be another way to recognize a strong acid or a strong base.
by Christina Chang 1C
Tue Jan 08, 2019 9:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.7
Replies: 5
Views: 118

Re: 11.7

Oh ok! Thank you! Do you also know if for part b it's the ratio of products to reactants?
by Christina Chang 1C
Tue Jan 08, 2019 9:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.7
Replies: 5
Views: 118

11.7

I was confused on what the difference was between the third and fourth flask because they both have equal amounts of product and reactant.

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