## Search found 49 matches

Sat Mar 15, 2014 8:25 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Final 2011, 1C
Replies: 3
Views: 717

### Final 2011, 1C

Why does ethane have a higher heat capacity than ethene? Also why NO has a greater residual entropy at 0 K than BF3?
Sat Mar 15, 2014 8:20 pm
Forum: Phase Changes & Related Calculations
Topic: 2011 Final, 1B
Replies: 1
Views: 406

### 2011 Final, 1B

Question says, 1 mol of methane is combusted irreversibly at contant room temp(25 celsius). Calculate the work.
What is the significance of irreversibility in the question? Also in the answer it says 2 mol is substituted but I don't understand why we put 2 moles, instead of 1 mol of methane?
Sat Mar 15, 2014 8:16 pm
Forum: Phase Changes & Related Calculations
Topic: Final 2011, question 1A
Replies: 2
Views: 456

### Final 2011, question 1A

In this question where does the 50 g come from? The question gives us these values, deltaH: -890 kJ/mol for methane gas, 50 mL water at 25 celsius, but it doesn't give the mass.
Sat Mar 15, 2014 4:22 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Winter Final 2010 Question 3A
Replies: 3
Views: 785

### Re: Winter Final 2010 Question 3A

Then, for a reaction to be spontaneous, should deltaS system be positive? Meaning that when the entropy is positive, there is more disorder?
Sat Mar 15, 2014 4:08 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 2010 Final 3A
Replies: 1
Views: 350

### 2010 Final 3A

Why is the sign of deltaSsystem for this reaction is negative?
2CO + O2 --> 2CO2
Sat Mar 15, 2014 1:05 pm
Forum: *Cyclopropanes and Cyclobutanes
Topic: Eclipsed Interactions in Cyclopropane
Replies: 1
Views: 527

### Eclipsed Interactions in Cyclopropane

How do we know how many eclipsed interactions there are in cyclopropane?
Sat Mar 15, 2014 12:26 pm
Forum: Phase Changes & Related Calculations
Topic: Sublimation and Fusion
Replies: 1
Views: 698

### Sublimation and Fusion

A solid has a dHsublimation 384.22 kJ/mol and dHvap 352.80 kJ/mol. What is the dHfusion for this compound?
Sat Mar 15, 2014 12:09 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate law in 3 step mechanism
Replies: 5
Views: 3875

### Re: Rate law in 3 step mechanism

Oh, so we took k3k2k1 all together and called the multiplication of three as k?
Fri Mar 14, 2014 11:03 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate law in 3 step mechanism
Replies: 5
Views: 3875

### Re: Rate law in 3 step mechanism

How do we do the subsitution in this question? I'm confused,
Thanks!
Fri Mar 14, 2014 11:02 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Quiz 2 8th question
Replies: 1
Views: 569

### Quiz 2 8th question

This question is from the friday 9 am class. 8th question asks us to make an arrhenius plot and wants us to calculate Ea using 37 Celsius and 60 Celsius values. Also wants us to calculate the rate sonstant at 190 Celsius. The given data are: Temp-37 C and Rate constant- 1.76 Temp-50 C and Rate const...
Fri Mar 14, 2014 10:56 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Quiz 2, friday 9 am class
Replies: 6
Views: 839

### Re: Quiz 2, friday 9 am class

So will this mean that less reactions will occur compared to the initial state,because of the temp decrease?
Thanks!
Fri Mar 14, 2014 10:54 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate law in 3 step mechanism
Replies: 5
Views: 3875

### Rate law in 3 step mechanism

How do we solve this question?

What is the rate law of the reaction?
Step 1: A+B <--> C (fast)
Step 2: C <--> D (fast)
Step 3: D --> E (slow)

Don't we just consider the slow step of this reaction when we find the rate law?
Fri Mar 14, 2014 10:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Quiz 2, friday 9 am class
Replies: 6
Views: 839

### Quiz 2, friday 9 am class

Regarding the 4th question that gives us a graph of number of collisions vs energy of reactants, the question asks how would the graph will change when the temp is lowered? So what will be the answer of this question? (There is a vertical line in the middle of the graph that shows the activation ene...
Thu Mar 13, 2014 4:10 pm
Forum: *Cycloalkenes
Topic: Final 2013 6a Numbering a hexene
Replies: 8
Views: 2313

### Final 2013 6a Numbering a hexene

Looking at 2013 final question 6A, why don't we write the name of this structure as 2,3,4,4 tetramethyl-cyclo-1-hexene? Shouldn't the double bond get the first number? Why do we give a methyl group, the first number?
Thu Mar 13, 2014 4:05 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Sn1 and Sn2 reactions
Replies: 1
Views: 531

### Sn1 and Sn2 reactions

Are we responsible for knowing what SN1 and SN2 reactions are in the final? If so, what are they and how do we distinguish them?
Thu Mar 13, 2014 1:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 7.19 Book Question
Replies: 2
Views: 498

### 7.19 Book Question

The question asks piece of copper with mass 20 g at 100 Celsius is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22 Celsius. Calculate the final temp of water.
How do we solve this question?
Tue Mar 11, 2014 11:26 pm
Forum: *Alkenes
Topic: Naming
Replies: 2
Views: 534

### Naming

Can CH3CHC(CH3)C(CH3)3 be also named as 3-methyl-4-dimethyl-2-pentene?
The answer says it is 3,4,4-trimethyl-2-pentene
Tue Mar 11, 2014 9:24 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Slow step
Replies: 4
Views: 3658

### Re: Slow step

Is it always that a fast step has an equilibrium mechanism, in which it can also have a reverse property?
Tue Mar 11, 2014 9:12 pm
Forum: Method of Initial Rates (To Determine n and k)
Replies: 3
Views: 540

How can a reaction be radical chain initiating? Do we look for a molecule with an unpaired electron as the product for this to happen?
Thanks!
Tue Mar 11, 2014 9:10 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Textbook Q 14.91
Replies: 1
Views: 601

### Textbook Q 14.91

This question involves a mechanism with 3 steps. The question asks which step is likely to be rate determining. Step 1: NO + NO--> N2O2 Step 2: N2O2+ H2--> N2O + H2O Step 3: N2O+ H2 --> N2 + H2O Also the overall rate of the reaction is : k(NO)^2(H2) Basically, the question asks us to find the slow s...
Tue Mar 11, 2014 8:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Replies: 3
Views: 540

What does is it mean to be radical chain initiating? This can be found on the question 14.77 in the text book.
Sun Mar 09, 2014 7:58 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 14.65 in Book Questions
Replies: 1
Views: 483

### 14.65 in Book Questions

For this reaction (2A<-->B+C) forward rate of formation of B is 265 L/molmin, and rate constant for reverse reaction is 392L/molmin. Activation energy for forward is 39.7 kJ/mol and for the reverse reaction is 25.4 kJ/mol. The question asks the equilibrium constant for the reaction and also whether ...
Sun Mar 09, 2014 7:33 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 14.53 Book Q- Large Equilibrium Constant
Replies: 1
Views: 547

### 14.53 Book Q- Large Equilibrium Constant

For a reaction with large equilibrium constant, is the rate constant of the of forward is much larger than the rate constant of the reverse reaction? Why is the answer to this is "yes"? What is the reasoning behind this?
Sun Mar 09, 2014 7:28 pm
Forum: Second Order Reactions
Topic: Book Q 14.37
Replies: 1
Views: 572

### Book Q 14.37

In this questions part b asks the time required for this reaction (A-->2B+C) to take place when Ao=0.15 M for the concentration of B to increase to 0.19 M when k=0.0035 (in the rate law for the loss of A). How do we solve this question? Also, what does it mean the rate law for loss of A? How do we s...
Sun Mar 09, 2014 12:01 am
Forum: First Order Reactions
Topic: 14.29 Book Q
Replies: 1
Views: 478

### 14.29 Book Q

In this question, the equation is A-->3B+C and when Ao=0.015 M, the concentration of B increases to 0.018 M in 3 min. The question asks the rate constant for the reaction as the rate loss of A.
How do we solve this question? What method do we use?
Sat Mar 08, 2014 11:30 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 14.19 in Book Q
Replies: 1
Views: 447

### 14.19 in Book Q

In this question I didn't understand how the order for B and C is 2. The reaction is A+B+C--> PRODUCTS. I thought they were 3 because if we look at C's concentration, it tripled from experiment 3 to 4, and the initial rate also increased by 9 times from 50.8 to 457. Why is the rate law of this react...
Sat Mar 08, 2014 11:19 pm
Forum: First Order Reactions
Topic: Units for rate constants
Replies: 1
Views: 456

### Units for rate constants

What are the units for rate constants in first order, second order and zero order reactions? (As in moles per liter and time in seconds etc.)
Sat Mar 08, 2014 11:17 pm
Forum: First Order Reactions
Topic: 14.11 From the Homework Book Q
Replies: 2
Views: 1324

### Re: 14.11 From the Homework Book Q

Thanks!!
Sat Mar 08, 2014 10:59 pm
Forum: First Order Reactions
Topic: 14.11 From the Homework Book Q
Replies: 2
Views: 1324

### 14.11 From the Homework Book Q

The question asks the initial rate of decomposition of N2O5 when 3.45 g of N2O5 is confined in a 0.750 L container and heated to 65 Celcius. (k=5.5x10^-4)
How do we solve this question? What method do we use? And also is 65 degree Celsius necessary in our calculations?
Fri Feb 28, 2014 12:21 am
Forum: First Order Reactions
Topic: Quiz 2 Prep 2013
Replies: 1
Views: 447

### Quiz 2 Prep 2013

Regarding the 8th question, how do we find new t and why don't we apply the first order equation by using 3.29 M as the initial concentration?
Fri Feb 28, 2014 12:16 am
Forum: General Rate Laws
Topic: Unit for time in the equations
Replies: 3
Views: 686

### Unit for time in the equations

When we are calculating time from the first,second and zero order reactions, is there a specific unit for time? Does it matter if its in seconds, minutes, days or years? Or will the question give the unit for us??
Thu Feb 27, 2014 10:15 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Quiz 2 Prep Winter 2013
Replies: 1
Views: 410

### Quiz 2 Prep Winter 2013

In the 1st question, why do we divide the rate by 2? Also by looking at the reaction, is it possible to determine the order of the reaction?
Thu Feb 27, 2014 9:25 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Quiz 2 Prep Winter 2012
Replies: 1
Views: 496

### Quiz 2 Prep Winter 2012

In the 4th and 5th question, how do we understand the reaction order by looking at Pt and ethylene? How do we determine the order??
Mon Feb 17, 2014 3:39 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 1
Views: 385

Regarding the example in the Course reader page 68, I didn't understand how we got 1/2 for Step 2 process and why it is not negative like in the usual formula (-1/a)? Also how did NO2 get into that equation?

Thanks!
Mon Feb 17, 2014 3:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Fast vs Slow
Replies: 1
Views: 378

### Fast vs Slow

Hi,
In a reaction, how do we distinguish the fast reaction from the slow reaction? In this case I'm referring to,
2NO + O2 -->2NO2 where the rate=k*(NO2)^2*(O2)
Tue Feb 11, 2014 10:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Quiz Question
Replies: 1
Views: 475

### Re: Quiz Question

Tue Feb 11, 2014 9:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 2011 Midterm Q1A
Replies: 3
Views: 531

### Re: 2011 Midterm Q1A

Thanks! :)
Tue Feb 11, 2014 9:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 2011 Midterm Q1A
Replies: 3
Views: 531

### 2011 Midterm Q1A

In 2011 midterm Q1A, why don't we use q=mCsdT equation since we are given the mass and the temperature change?
Tue Feb 11, 2014 8:30 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: 2010 Midterm Q3B
Replies: 2
Views: 461

### Re: 2010 Midterm Q3B

Thank you!
Tue Feb 11, 2014 8:22 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: 2010 Midterm Q3B
Replies: 2
Views: 461

### 2010 Midterm Q3B

Why in an expansion against vacuum, the external pressure and the work equals to zero?
Tue Feb 11, 2014 7:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Quiz 1 Prep Workbook, Q8
Replies: 1
Views: 267

### Quiz 1 Prep Workbook, Q8

Regarding the Work Book Quiz 1 Prep 8th question, it asks which compound has the higher molar entropy ( ch3br vs. ch3f)
How do we understand the molar entropy just by looking at the compound? Is it about compound's structure?

Thanks!
Mon Feb 10, 2014 8:02 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Midterm 2009 # 8
Replies: 3
Views: 586

### Re: Midterm 2009 # 8

Why do we plug in 0.025693 instead of plugging in 0.0592 into the nerst equation in this question?
Mon Feb 10, 2014 6:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 2009 midterm Q1
Replies: 1
Views: 282

### 2009 midterm Q1

Regarding the winter midterm 2009 Q1, why are we neglecting the negative sign after finding delta H? Why don't we continue with our calculations with -3069?
Thanks!
Mon Feb 10, 2014 6:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 2008 midterm 5b
Replies: 1
Views: 202

### 2008 midterm 5b

In 2008 midterm 5b, would sodium sulfide react with solid Cd? Or would it react with Cd+2? And why would the cell potential increase, I couldn't understand..
Thanks!
Mon Feb 10, 2014 6:29 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs Irreversible
Replies: 4
Views: 652

### Reversible vs Irreversible

Hi, What does it mean exactly that "the process is reversible" or "irreversible" and why in a reversible process, delta S total equals to zero? Also what kind of equations should we consider while doing a reversible and an irreversible process? (Ex. Delta S=0 for reversible) Than...
Sun Feb 09, 2014 11:37 am
Forum: Phase Changes & Related Calculations
Topic: Quiz 1 Q 8
Replies: 3
Views: 521

### Re: Quiz 1 Q 8

So for steps 1 and 3, which pressure do we plug into the equation? Is it the final pressure? Also does that equation of w=-nRTln(T2/T1) equals to w=-PdVln(T2/T1) then?
Sun Feb 09, 2014 10:51 am
Forum: Phase Changes & Related Calculations
Topic: Quiz 1 Q 8
Replies: 3
Views: 521

### Quiz 1 Q 8

This the quiz from Friday 9 am class. For the 8th question, how do we calculate heat? How do we integrate the change in pressure to the calculation for A to B, and D to C?
Sun Feb 09, 2014 10:47 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Question from Friday's 9 am class quiz
Replies: 1
Views: 303

### Question from Friday's 9 am class quiz

Regarding the Quiz from Friday at 9 am, the 6th question that starts with ''the entropy of vaporization of compound X...'', what is the significance of temperature in this question? And how do we solve this question?

Thanks!
Sat Feb 08, 2014 4:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 7.43
Replies: 1
Views: 261

### 7.43

Regarding the 7.43 question on the book, what is the significance of the excess sulfur in part b? Also what method do we use to solve this question's part b and c?
Thank you!