## Search found 30 matches

Mon Mar 12, 2018 4:54 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 165

We will not need to know how to do steady state approximation for the final, since Dr. Lavelle did not teach it in class and said that it would take way too long to do. Therefore, we only have to know the pre-equilibrium approach, which should get the same result anyways.
Mon Mar 12, 2018 4:45 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Resonance and Entropy
Replies: 2
Views: 644

### Re: Resonance and Entropy

Yes more resonance structures means that it has a higher residual entropy. Since residual entropy S= kblnW in which W is the degeneracy of a molecule, a greater number of possible structures would result in a greater W and thus higher residual entropy. Hope that helps!
Mon Mar 12, 2018 4:41 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.49
Replies: 5
Views: 622

### Re: HW 15.49

KayleeMcCord1F wrote:What's an example of a situation when an intermediate would be considered in the overall rate law?

An intermediate would never be in the overall rate law. You would have to substitute it out using the pre-equilibirium approach.
Mon Mar 05, 2018 7:59 pm
Forum: Second Order Reactions
Topic: 15.17
Replies: 4
Views: 352

### Re: 15.17

therefore, is it safe to say that you DO NOT calculate the order of C because it is independent of the rate?? in other words, only the orders of A and B matter because they affect the rate Well when you determine that the concentration of C is independent of the reaction rate, then you are essentia...
Mon Mar 05, 2018 7:55 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: "Slow" Step Only?
Replies: 4
Views: 293

### Re: "Slow" Step Only?

A reaction can only proceed as fast as its slowest step and thus only the slow step contributes to the reaction rate and thus also rate law. Hope this helps!
Mon Mar 05, 2018 7:46 pm
Forum: Experimental Details
Topic: Rate Constant
Replies: 4
Views: 597

### Re: Rate Constant

Yes after you have found the order of each reactant (to write the rate law), you can just take the values of any experiment and plug them into the rate law to find k. Hope this helps!
Mon Feb 26, 2018 2:13 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated [ENDORSED]
Replies: 3
Views: 459

### Re: Isolated[ENDORSED]

Since the universe is everything, it has no surroundings and thus no energy or matter can leave/enter the system, which in this case is the universe.
Mon Feb 26, 2018 2:11 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q4A [ENDORSED]
Replies: 4
Views: 336

### Re: Midterm Q4A[ENDORSED]

Yes this can be confusing because the problem did not explicitly state whether pressure was constant or not. However, I guessed that it was because it said that the EXTERNAL pressure was 0.5 atm and usually external pressure stays constant.
Mon Feb 26, 2018 1:59 pm
Forum: First Order Reactions
Topic: First order reactions vs second order reactions [ENDORSED]
Replies: 3
Views: 433

### Re: First order reactions vs second order reactions[ENDORSED]

In a first order reaction, doubling the concentration of the reactant will double the rate of the reaction. In a second order reaction, doubling the concentration of the reactant will quadruple the rate of the reaction. Hope this helps!
Mon Feb 19, 2018 8:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.19
Replies: 1
Views: 118

### Re: 14.19

Because the equation is actually E(cell)= E(cathode) - E(anode)
Thus, E(cathode)= E(cell) + E(anode) = -0.689+0.34 = -0.349 V

Hope this helps!
Mon Feb 19, 2018 8:35 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.37
Replies: 2
Views: 276

### Re: 14.37

The equations that you mentioned (2.303RT/nF and 0.0592/n) is with LOG of Q while the solution manual uses LN of Q. Therefore, all three of these equations are actually equivalent. Hope that clarifies it!
Mon Feb 19, 2018 8:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells vs Electrochemical Cells
Replies: 4
Views: 425

### Re: Galvanic Cells vs Electrochemical Cells

Yes there is a difference. Electrochemical is the overarching term for both galvanic (voltaic) and electrolytic cells. Galvanic cells refer specifically to cells that use spontaneous redox reactions to create electrical energy, while electrochemical cells can also refer to cells that use electrical ...
Mon Feb 12, 2018 2:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs = 0
Replies: 2
Views: 208

### Re: Gibbs = 0

Yes you set deltaG equal to 0 when the reaction is at equilibrium, and you do it in this case because H20 is changing from liquid to vapor and vapor to liquid at equal rates at 100 degrees C (its normal boiling point).
Mon Feb 12, 2018 2:15 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.35 number of moles question [ENDORSED]
Replies: 1
Views: 220

### Re: 9.35 number of moles question[ENDORSED]

Containers B and C have diatomic molecules. The problem states that these containers have one mole of ATOMs, and since it takes two atoms to create one diatomic molecule, then you will only have .5 mol of molecules in the containers. Hope that helps!
Mon Feb 12, 2018 2:10 pm
Forum: Calculating Work of Expansion
Topic: Heating at Constant Pressure
Replies: 2
Views: 188

### Re: Heating at Constant Pressure

When it says heating at a constant pressure, it refers to the pressure of the system. However, if it is an open system (such as a flask or test tube), then the pressure of the system is the same as the pressure of the surroundings.
Tue Feb 06, 2018 5:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free energy
Replies: 1
Views: 131

### Re: Gibbs Free energy

Yes Gibbs free energy is lowest as a solid because it takes heat and a positive deltaH for the substance to go from a solid to a liquid and from a liquid to a gas. So even though the entropy might be greater as a gas, the enthalpy is higher so the overall G is higher in gases.
Tue Feb 06, 2018 4:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.99 math
Replies: 2
Views: 228

### Re: 8.99 math

The 800 g comes from the mass of the solution. You know this because the problem says that the density of the solution is the same as water (1 g/mL) and since the solution has a volume of 800 mL, then it has a mass of 800 g. Hope this helps!
Tue Feb 06, 2018 4:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83
Replies: 3
Views: 509

### Re: 11.83

You should be able to use the same equation and values and just change T to get the right answer. Just make sure you use Kelvin!
Fri Feb 02, 2018 2:01 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Question 8.13
Replies: 3
Views: 199

### Re: Question 8.13

It is important that the question clarifies that it is an irreversible process because it tells us which equation to use. Because it is irreversible, we can use the equation w=-p(delta V), rather than the equation w=-nRTln(V2/V1) for reversible processes.
Fri Feb 02, 2018 1:58 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: reversible vs irreversible
Replies: 3
Views: 290

### Re: reversible vs irreversible

Work can certainly be done in both reversible and irreversible processes, but more work is done in reversible processes. Work and entropy relate through the equation deltaS=-w/T.
Fri Feb 02, 2018 1:52 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Exergonic [ENDORSED]
Replies: 5
Views: 270

### Re: Exergonic[ENDORSED]

Other examples of exergonic reactions are most, if not all, catabolic reactions, which are reactions where larger molecules are broken down into smaller molecules. These processes give off heat, meaning they are exergonic.
Fri Jan 26, 2018 2:15 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.49
Replies: 5
Views: 354

### Re: 8.49

Helen Shi 1J wrote:Since using Kelvin or Celcius will give different answers, which one should we use?

I would definitely use Kelvin, but if you're only calculating the change in temperature, you can use either Kelvin or Celsius.
Fri Jan 26, 2018 2:12 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: constant pressure
Replies: 5
Views: 266

### Re: constant pressure

Would you have to take into account the number of moles of gas in relation to the balanced equation when solving for q ? Yes it depends on how many moles the question says are reacting. For example, if the question says to find q when 3 moles of C2H6 are reacting, but your balance equation has only...
Fri Jan 26, 2018 2:07 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Monatomic Gas
Replies: 5
Views: 391

### Re: Monatomic Gas

Julie Steklof 1A wrote:Does this mean that the specific heat for all ideal monatomic gases is equal?

The molar heat capacity for ideal monatomic gases will be equal, not the specific heat capacity though.
Wed Jan 17, 2018 9:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 5
Views: 305

### Re: Hess's Law

Hess's Law states (according to the book) that "the overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided." For example, if you the enthalpies of two reactions that make up one overall reaction, you can find the enthalpy of the ...
Wed Jan 17, 2018 9:20 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity of Gases
Replies: 2
Views: 132

### Re: Heat Capacity of Gases

The equation Cv,m=3/2R refers to the molar heat capacity for an atom/monatomic gas at constant volume. Pg 281 of the textbook has some good info on it and a nice chart haha
Wed Jan 17, 2018 9:16 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.1 question
Replies: 8
Views: 476

### Re: 8.1 question

The question calls it a "very high quality" thermos bottle, so I think that it wants you to assume that the coffee is perfectly insulated. Therefore, no heat would be transferred in or out, making it an isolated system. Hope this helps!
Thu Jan 11, 2018 10:37 pm
Forum: Phase Changes & Related Calculations
Topic: Superheating
Replies: 6
Views: 1330

### Re: Superheating

I don't think superheating or supercooling is very common, but there are multiple different variables that can cause them to happen. One example of superheating is how when you microwave water in a glass bowl, the temperature must be greater than 100 degrees C in order for the water to boil. This is...
Thu Jan 11, 2018 10:29 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Sublimation
Replies: 4
Views: 304

### Re: Sublimation

Sublimation is when a substance changes from a solid directly to a vapor, effectively skipping the liquid phase. This obviously isn't super common, but a well-known example is dry ice. I would say an important concept to know is that the enthalpy of sublimation can be calculated with the sum of the ...
Wed Jan 10, 2018 5:15 pm
Forum: Administrative Questions and Class Announcements