Search found 34 matches

by Chew 2H
Sat Mar 17, 2018 11:51 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Concentration cells
Replies: 2
Views: 233

Concentration cells

For concentration cells with different concentration, why does the product has to have lesser concentration than the reactant when we write the overall reactions?
by Chew 2H
Wed Mar 14, 2018 2:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E cell value
Replies: 2
Views: 171

Re: E cell value

Thank you! And if it wasn't a galvanic cell, and the overall E could be negative. how do we know which one to flip?
by Chew 2H
Wed Mar 14, 2018 2:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E cell value
Replies: 2
Views: 171

E cell value

In the second electrochem problem Lavelle went through today in lecture, why did we flip the E value for the second equation? Do we always flip the equation with a much more negative value?
by Chew 2H
Sun Mar 11, 2018 11:25 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Ways to approach reaction mechanism
Replies: 2
Views: 158

Ways to approach reaction mechanism

In lecture, Lavelle went through the 3 ways to to calculate reaction mechanism, Steady state, pre equilibrium and the "direct computation: solve for differential equations". What exactly is the "direct computation" approach. I'm kinda confused.
by Chew 2H
Sun Mar 11, 2018 11:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates in Rate law
Replies: 3
Views: 838

Intermediates in Rate law

Clarification:
When we write rate law based on order, we only include the intermediates if we're writing the rate law for the specific reaction (say step 1 or step 2) right? If it's the overall reactions, we always have to cancel out the intermediates?
by Chew 2H
Sun Mar 11, 2018 11:14 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: K and K'
Replies: 4
Views: 212

Re: K and K'

is there a way to numerically calculate k' from k without knowing the K?
by Chew 2H
Mon Mar 05, 2018 3:27 pm
Forum: Second Order Reactions
Topic: 15.35
Replies: 2
Views: 182

15.35

For 15.35 part a, the half life for the second order reaction of a substance A is 50.5s when [A]initial is 0.84M. it then asks us to calculate the time needed for the concentration of A to decrease to one sixteenth of its original value. For this question why can't we just multiply 50.5s by 4 like w...
by Chew 2H
Sun Mar 04, 2018 5:19 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.29
Replies: 1
Views: 106

15.29

when we express the loss of one reactant corresponding to the coefficient of another reactant (like we did in 15.29) , does it only work for first order reactions?
by Chew 2H
Sun Mar 04, 2018 4:36 pm
Forum: First Order Reactions
Topic: half life
Replies: 2
Views: 181

half life

is half life an extensive or intensive property?
by Chew 2H
Wed Feb 28, 2018 4:37 pm
Forum: Zero Order Reactions
Topic: Units [ENDORSED]
Replies: 7
Views: 1031

Re: Units [ENDORSED]

There's also one using kPA/sec. Does anyone know how kPA relates to the rate of reactions?
by Chew 2H
Wed Feb 28, 2018 4:35 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: When do we calculate for k
Replies: 3
Views: 194

When do we calculate for k

I've seen problems that uses k either from the value given in the textbook or by calculating it. how do we know when we calculate for it ourselves and when we simply use the table provided in the textbook?
by Chew 2H
Wed Feb 28, 2018 4:28 pm
Forum: Second Order Reactions
Topic: positive slope in second ordre graph
Replies: 2
Views: 200

positive slope in second ordre graph

Could someone explain why there is a positive linear slope for the second order reaction while the slopes are both negative for zero order and first order? Wouldn't the positive slope mean that the concentration in increasing? I'm alittle confused
by Chew 2H
Tue Feb 20, 2018 2:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 1
Views: 107

Salt Bridge

Could someone help explain what exactly happens in the salt bridge as well as with what it does to the reaction? I'm not clear on how the ions gets transferred across it.
by Chew 2H
Tue Feb 20, 2018 2:21 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.91 Electrolyte
Replies: 2
Views: 183

Re: 14.91 Electrolyte

i think this is referring to the external wire circuit. From what i know, salt bridges don't exist in Electrolytic cells.
by Chew 2H
Tue Feb 20, 2018 2:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: electrolysis
Replies: 1
Views: 121

electrolysis

How much of Electrolysis are we supposed to know regarding the test this week?
by Chew 2H
Mon Feb 12, 2018 5:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode/ Cathode
Replies: 6
Views: 317

Anode/ Cathode

In the anode/cathode diagram we saw, is Anode always on the left side or can it be switched? If so, how would we know which is which?
by Chew 2H
Sun Feb 11, 2018 11:02 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Monoatomic Ideal Gases
Replies: 1
Views: 101

Monoatomic Ideal Gases

What exactly are monoatomic ideal gases? When finding the Cv of F2, would we use 3/2R or 5/2R?
by Chew 2H
Sun Feb 11, 2018 10:53 pm
Forum: Calculating Work of Expansion
Topic: different ways to calculate w
Replies: 4
Views: 243

different ways to calculate w

when do we use -PdeltaV and when do we use -nRTln(V2/V1) in calculating w? What's the difference between the two?
by Chew 2H
Wed Feb 07, 2018 5:42 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: K to Kc equation
Replies: 2
Views: 150

K to Kc equation

In the equation that converts K to Kc, what does the "c" represent?
by Chew 2H
Wed Feb 07, 2018 2:23 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Predicting signs of entropy [ENDORSED]
Replies: 1
Views: 123

Predicting signs of entropy [ENDORSED]

I understand that going from solid to gas from reactant to product would lead to an increase in entropy. I also understand that increase in number of moles lead to an increase in entropy. But what happens when a reaction has an increase in the number of moles but also goes from gas to solid in the p...
by Chew 2H
Tue Feb 06, 2018 11:46 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15
Replies: 4
Views: 255

9.15

Could someone help with how to solve 9.15? I'm not sure where to start
by Chew 2H
Wed Jan 31, 2018 3:16 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Gibbs free energy which method is the most accurate? [ENDORSED]
Replies: 1
Views: 209

Gibbs free energy which method is the most accurate? [ENDORSED]

Would the values of deltaG be the same regardless of which method is being used to calculate it or is there one that is less accurate than others?
by Chew 2H
Wed Jan 31, 2018 3:04 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Entropy Change factors
Replies: 6
Views: 318

Re: Entropy Change factors

Would the value of entropy differ based on bond strength as well? Would there be less entropy in a triple bond than in a single bond?
by Chew 2H
Wed Jan 31, 2018 3:00 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Phase change question demonstrated in Lecture
Replies: 4
Views: 300

Phase change question demonstrated in Lecture

In the lecture, Dr Lavelle went over the phase change problem from Br(l)--> Br(g). There, he talked about how deltaH + is a endothermic reaction that does not favor forward processes. I understand that deltaH + refers to reactions being spontaneous at high temperature but what did Dr Lavelle mean by...
by Chew 2H
Mon Jan 22, 2018 9:43 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Capacity from Heating Curve
Replies: 2
Views: 163

Re: Heating Capacity from Heating Curve

Because Heating capacity refers to the amount of temperature required to raise a certain substance by 1 degree celcius, lower heat capacity means higher rise in temperature over once heated. So on the heating curve, the temperature rises higher thus making the slope of the curve steeper.
by Chew 2H
Mon Jan 22, 2018 4:25 pm
Forum: Phase Changes & Related Calculations
Topic: enthalpy of phase change
Replies: 1
Views: 103

enthalpy of phase change

In the question Dr Lavelle showed us in lecture, Br2(l) --> 2Br(g), i understand that we have to add the enthalpy of vaporization with the bond enthalpies. But what would the enthalpy of vaporization be? is it the normal n*heat of vaporization or is there another way of it?
by Chew 2H
Mon Jan 22, 2018 3:25 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and Work relation
Replies: 6
Views: 327

Heat and Work relation

Based on the deltaU=q+w equation, if a system is endothermic and q is positive, would the work always be negative? If not, when does it become positive?
by Chew 2H
Wed Jan 17, 2018 5:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Born Haber
Replies: 2
Views: 161

Born Haber

Do we need to know the born haber cycle for the test?
by Chew 2H
Wed Jan 17, 2018 4:16 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Energy Change in an Isolated System
Replies: 4
Views: 248

Re: Energy Change in an Isolated System

So does that mean deltaU=q+w does not apply to an isolated system?
by Chew 2H
Wed Jan 17, 2018 4:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Extensive vs. Intensive
Replies: 3
Views: 160

Re: Extensive vs. Intensive

Extensive properties depend on the amount of the substance so basically an example would be Heat Capacity (the amount of heat required to change the temp by 1 Degree celcius of a substance. But for intensive properties (which are much more useful), it would be things like specific heat capacity or m...
by Chew 2H
Wed Jan 17, 2018 4:01 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bong Enthalpy accuracy [ENDORSED]
Replies: 3
Views: 169

Bong Enthalpy accuracy [ENDORSED]

Why again are bond enthalpies the least accurate? In exams, do we always try to use Hess Law unless told otherwise?
by Chew 2H
Thu Jan 11, 2018 1:43 pm
Forum: Phase Changes & Related Calculations
Topic: Hess Law [ENDORSED]
Replies: 5
Views: 309

Hess Law [ENDORSED]

In Hess Law, if we flip the equation product reactant-wise, do we take the reciprocal of the enthalpy value or multiply it by '-'?
by Chew 2H
Wed Jan 10, 2018 5:52 pm
Forum: Phase Changes & Related Calculations
Topic: Reaction in a Flask
Replies: 5
Views: 458

Re: Reaction in a Flask

Endothermic reaction in a flask feels cool because endothermic reactions use up energy(heat) from the surrounding. Therefore the surroundings loses heat and cools down.
by Chew 2H
Wed Jan 10, 2018 5:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heating Curve: How is the kJ calculated?
Replies: 2
Views: 127

Heating Curve: How is the kJ calculated?

In the Heating Curve shown in lecture today, how do we know kJ/mol values of each solid/liquid/gas phases depending on the temperatures? Will it always be given?

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