## Search found 19 matches

Tue Feb 13, 2018 12:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.99 Bond dissociation energy
Replies: 1
Views: 101

### 11.99 Bond dissociation energy

I was wondering if anyone knows if the values for bond dissociation energy will be provided or if we have to solve for it. The values are listed as part of the answer for 11.99 a) in the solutions manual. If we aren't provided those values, what is the method for solving for it?
Sat Feb 10, 2018 1:35 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units Confusion [ENDORSED]
Replies: 3
Views: 225

### Re: Units Confusion[ENDORSED]

I'm having the same problem. For example with homework problem 9.19 the equation delta-S = nCln(T2/T1) is used. However, in this case they just ignored the n so the resulting answer ended up in J/(k x mol). I thought that when they don't give the number of moles and you are using this equation, you ...
Sat Feb 10, 2018 1:25 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework problem 9.25: orientations of a molecule
Replies: 2
Views: 174

### Homework problem 9.25: orientations of a molecule

In order to solve homework question 9.25, you need to first determine the number of possible molecular orientations. I'm wondering if the only way to figure it out is to draw them all. Is there a math based way or any faster way to determine it?
Sat Feb 10, 2018 1:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: When to use + sign
Replies: 11
Views: 517

### When to use + sign

I noticed in the solutions manual that sometimes a + sign is used for a positive change in something and sometimes it isn't. How do I know when to use it and when not to?
Thu Feb 01, 2018 9:22 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: heat capacities
Replies: 5
Views: 377

### Re: heat capacities

The energy gained by the ice is equal to the energy lost by the water. However, if the water has enough energy to heat the ice to 0 degrees C and melt it, then to get the melted ice to the final temperature you will need to use the specific heat of liquid water even though it would be on the same si...
Thu Feb 01, 2018 9:14 am
Forum: Phase Changes & Related Calculations
Topic: Calculating the Change in Enthalpy
Replies: 4
Views: 274

### Re: Calculating the Change in Enthalpy

It's also important to know which direction the phase changes are occurring because you may have to multiply the delta-H by -1 if you are freezing instead of melting for fusion or if you are condensing instead of vaporizing for vaporization.
Thu Feb 01, 2018 9:08 am
Forum: Phase Changes & Related Calculations
Topic: Phase Change Diagrams: Slopes
Replies: 2
Views: 160

### Phase Change Diagrams: Slopes

When drawing the phase change diagram for a given substance, how do we determine the steepness of the gas, liquid, and solid phases? Also, how do you know which line you draw longer, the heat of vaporization or the heat of fusion?
Thu Feb 01, 2018 8:57 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity
Replies: 3
Views: 237

### Re: Heat Capacity

Thermal equilibrium only occurs when the temperatures of the objects are the same. It does not matter how long it would take for the temperatures to even out, but equilibrium will not be established until then.
Fri Jan 26, 2018 12:22 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question regarding ice in water?
Replies: 2
Views: 214

### Re: Question regarding ice in water?

In those certain problems that we are dealing with, they have to either give us the final temperature of the system, or the total heat transferred between the ice and the water. With either of these pieces of information, you should be able to determine if the ice will completely melt.
Fri Jan 26, 2018 12:14 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy equations
Replies: 4
Views: 275

### Re: Gibbs free energy equations

They are two ways to find the standard gibbs free energy of a reaction. However, depending on the information you are given to start with and what you are trying to solve for, you may want to use one over the other.
Fri Jan 26, 2018 12:05 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Bomb calorimeter
Replies: 7
Views: 391

### Re: Bomb calorimeter

All the above is correct. It being an isolated system is extremely important and is why bomb calorimeters are extremely useful. This allows for the very accurate calculation of the energy released when a substance has been combusted.
Fri Jan 26, 2018 12:00 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: constant pressure
Replies: 5
Views: 252

### 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 ?
Thu Jan 18, 2018 8:27 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: PdeltaV=deltanRT
Replies: 4
Views: 1651

### Re: PdeltaV=deltanRT

You can only use this equation when you are dealing with an ideal gas. The deltas imply that a change is occurring. You can use this in these 2 formulas:

delta H = delta U + nR (delta T)
delta H = delta U + (delta n) RT
Thu Jan 18, 2018 8:18 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Work vs. Heat
Replies: 6
Views: 396

### Re: Work vs. Heat

The difference between velocity and speed is something we don't really need to think about in this course. While both q and w have units of energy (typically J or kJ) when used in the 1st law of thermo equation, q and w are quite different. q is heat which has to do with the thermal energy and w is ...
Thu Jan 18, 2018 8:11 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: State function in relation to heat
Replies: 3
Views: 241

### Re: State function in relation to heat

q is the general symbol we use for heat and it is a path dependent function. H is the general symbol for enthalpy and it has the definition of H = U + PV which is derived from the 1st law of thermodynamics. H is a state function while q is a path dependent function. This is why in many of the proble...
Thu Jan 18, 2018 3:50 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated system
Replies: 8
Views: 477

### Re: Isolated system

An isolated system has no contact with its surroundings. The way the book puts it is that an isolated system can exchange nothing (neither work nor matter) with its surroundings.
Thu Jan 11, 2018 8:09 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Celsius the same as Kelvin? [ENDORSED]
Replies: 9
Views: 2566

### Celsius the same as Kelvin?[ENDORSED]

Question number 8.25 states that there is a temperature rise of 7.32 C. Why is it that because the degree Celsius is the same size as the degree kelvin, “per C” is the same as “per K" ? Isn't it normally that to convert Celsius to Kelvin you have to add 273.15 ?
Wed Jan 10, 2018 8:54 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: First Law and Calculating Final Temp (question 8.21)
Replies: 3
Views: 249

### First Law and Calculating Final Temp (question 8.21)

Question 8.21 states, "A piece of copper of mass 20.0 g at 100.0 degrees C is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22.0 degrees C. Calculate the final temperature of the water. Assume that no energy is lost to the surroundings." The solutions m...
Wed Jan 10, 2018 7:43 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cp,m --> Cv,m
Replies: 2
Views: 457

### Re: Cp,m --> Cv,m

The book describes how they derived it in the "How Do We Do That?" box on page 280