## Search found 23 matches

Sun Mar 18, 2018 10:39 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cp and Cv
Replies: 5
Views: 420

### Re: Cp and Cv

CP,m = CV,m + R

Or, the molar heat capacity at constant pressure is equal to the molar heat capacity at constant volume plus the gas constant.
Sun Mar 18, 2018 1:14 am
Forum: Calculating Work of Expansion
Topic: Reversible vs. Irreversible
Replies: 2
Views: 294

### Re: Reversible vs. Irreversible

Irreversible reactions do less work because they happen fast and lose energy to heat, friction, etc. Reversible reactions happen very slowly, but make sure that all the energy is actually going to the expansion work.
Sun Mar 18, 2018 12:33 am
Forum: Calculating Work of Expansion
Topic: Work Equations: Which One to Use?
Replies: 3
Views: 334

### Re: Work Equations: Which One to Use?

You use w = - pex∆V when external pressure is constant. You use w = - nRT ln(V2/V1) when pressure is variable, or not constant.
Sat Mar 17, 2018 10:55 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Standard enthalpy change
Replies: 2
Views: 272

### Re: Standard enthalpy change

The reaction you need to calculate ∆H for has 4 moles NO, but in the reaction given, the stoichiometric coefficient of NO is 2, so in order to calculate the ∆H that is asked of you, you need to multiply the q (which is for the stoichiometric coefficients in the given reaction) by 2.
Sat Mar 17, 2018 9:54 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: how to find a microstate
Replies: 2
Views: 481

### Re: how to find a microstate

In order to know how many micro-states a molecule has, you have to know its Lewis structure and molecular geometry. Once you know its molecular geometry, think about how you can rotate the molecule/move atoms around such that you haven't changed the molecule itself. For example, FClO 3 is tetrahedra...
Sat Mar 17, 2018 9:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing vs Oxidizing Agents
Replies: 4
Views: 381

### Re: Reducing vs Oxidizing Agents

The way I remember is by using the acronym LEO says GER, which stands for Losing Electrons is Oxidation and Gaining Electrons is Reduction. So, if a substance loses electrons, then it has been oxidized. If a substance has been oxidized, then it inevitably causes reduction in another substance, becau...
Sat Mar 17, 2018 9:10 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Midterm 2b: relationship between delta H and q
Replies: 1
Views: 279

### Re: Midterm 2b: relationship between delta H and q

I got full points for 2b and I said "The reactants start with 1 mole of solid & 6 moles of gas, while the products consist of 6 moles of liquid & 6 moles of gas. The entropy of liquid is greater than the entropy of solid, and there are 6x as many particles of liquid as there are of the ...
Sat Mar 17, 2018 9:01 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G units
Replies: 3
Views: 1874

### Re: Delta G units

The answer to this can be found on page 571 of the textbook in the green box. The more technical form of the equation is written as ∆G r = - n r FE where the subscript r represents the "molar" form where n is plugged in as just a number, without the mole units. So, if there were 2 moles, t...
Sat Mar 17, 2018 8:49 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: what does W stand for in S=klnW
Replies: 3
Views: 2705

### Re: what does W stand for in S=klnW

W stands for the number of ways that the atoms/molecules in a sample can be arranged and give the same total energy. Quantitatively, W = (# of micro-states) (# of particles in the system) . A micro-state is just a different way of arranging the atoms. So, in example 9.7 on page 331, C-O is o...
Mon Feb 19, 2018 3:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous Membrane vs. Salt Bridge
Replies: 1
Views: 281

### Porous Membrane vs. Salt Bridge

Does using a porous membrane versus a salt bridge make a difference to the reaction? I know a porous membrane uses the ions from the original electrolytic solutions to complete the electrical circuit, but a salt bridge uses a separate ionic solution to complete the electrical circuit. Does it matter...
Tue Feb 13, 2018 2:13 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G Units
Replies: 1
Views: 166

### Delta G Units

So, I'm confused whether Gibbs free energy is reported in kJ or kJ/mole. I know that molar Gibbs free energy implies kJ/mole. But standard Gibbs free energy is just reported in kJ (such as example 9.14, 9.15). But standard Gibbs free energy of formation is reported kJ/mole. Also, from 11.3, I know t...
Tue Feb 13, 2018 12:04 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Example 9.8
Replies: 2
Views: 176

### Re: Example 9.8

In Boltzmann's equation S = k ln(W), W is defined as the number of ways that atoms/molecules can be arranged and still give the same total energy. What this means mathematically is that W = (# of micro states) (# of particles) . So, in example 9.8, the FClO 3 molecule can be arranged 4 diffe...
Mon Feb 12, 2018 11:52 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Example Problem 8.6
Replies: 1
Views: 154

### Re: Example Problem 8.6

For part A, since the the system is at constant volume and a given pressure (1 atm) is given, the only change you have to worry about is the change in temperature (or the heat transfer). For part B, since the system is at constant pressure, that means volume is free to change, so you have to worry a...
Sat Feb 10, 2018 9:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49 STP vs. SATP
Replies: 2
Views: 254

### 8.49 STP vs. SATP

Given: OF 2 (g) + H 2 O(g) --> O 2 (g) + 2HF(g) Delta H = - 318 kJ Question: What's the change in internal energy for the reaction of 1 mole OF 2 ? So, you have to find what -P*Delta V equals using the ideal gas equation, but I'm not sure what temperature you're supposed to use. The solutions manual...
Sat Feb 10, 2018 6:15 pm
Forum: Balancing Redox Reactions
Topic: Oxidation vs. reduction
Replies: 8
Views: 323

### Re: Oxidation vs. reduction

To add on to the previous answer, something to note is that the substance that is 'oxidized' is also known as the 'reducing agent', and the substance that is 'reduced' is also known as the 'oxidizing agent'. This is because a substance that experiences oxidation (or the loss of electrons) inherently...
Tue Feb 06, 2018 1:42 pm
Forum: Balancing Redox Reactions
Topic: 14.5
Replies: 3
Views: 318

### 14.5

The directions are to balance the redox reaction in basic solution. Part a writes: Action of ozone on bromide ions, O3 (aq) + Br - (aq) --> O2 (g) + BrO3 - (aq).

Why does the solutions manual write the first half-reaction as: O3 (g) --> O2 (g)?

Don't both O3 and O2 have oxidation numbers of 0?
Mon Jan 29, 2018 9:44 pm
Forum: General Science Questions
Topic: Significant Figures
Replies: 2
Views: 414

### Significant Figures

In problem 9.1, the question states "A human body generates heat at the rate of about 100. (J・s^-1). At what rate does your body heat generate entropy in your surroundings, taken to be at 20. (degrees Celsius)?" The solutions manual wrote the answer as 0.341 (J・K^-1・s^-1) Since 20. (degree...
Sun Jan 21, 2018 11:43 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: closed sysytem
Replies: 3
Views: 215

### Re: closed sysytem

A mercury thermometer is a closed system because the mercury never leaves the thermometer, nor does any matter enter the thermometer. Only energy is transferred between the thermometer and its surroundings. As the mercury thermometer gains energy, that is what causes the mercury to rise and ultimate...
Sun Jan 21, 2018 10:42 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Converting L·atm to Joules
Replies: 3
Views: 6191

### Re: Converting L·atm to Joules

The conversion factor between L・atm and joules is: 1 L・atm = 101.325 J (This is an exact conversion)
Sun Jan 21, 2018 9:22 pm
Forum: Phase Changes & Related Calculations
Topic: Irreversible vs reversible
Replies: 3
Views: 223

### Re: Irreversible vs reversible

Consider a gas expanding inside a piston. Assume the external pressure is equal to the internal pressure. Let's say the goal is to expand the volume of the gas by 1 L. Theoretically, in a reversible process, you would reduce the external pressure by an infinitesimally small amount. The internal pres...
Sun Jan 21, 2018 8:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exercise 8.29
Replies: 1
Views: 135

### Re: Exercise 8.29

The main idea behind this question is that heat capacity increases with molecular complexity. The explanation in the solutions manual states that as more atoms are present in the molecule, there are more possible bond vibrations that can absorb added energy. Some people explain this using molecular ...
Sun Jan 21, 2018 7:59 pm
Forum: Phase Changes & Related Calculations
Topic: Irreversible and Reversible
Replies: 7
Views: 404

### Re: Irreversible and Reversible

From what Lavelle has posted on his website, questions regarding the idea/concept of reversible and irreversible processes are fair game. He has explicitly said that calculations using w = - nRT ln(Vfinal/Vinitial) will not be on Test 1. However, I would highly suggest being able to explain to anoth...
Sun Jan 21, 2018 4:54 pm
Forum: Calculating Work of Expansion
Topic: Reversible vs. Irreversible Process
Replies: 2
Views: 580

### Re: Reversible vs. Irreversible Process

A reversible process is one that is infinitely slow. Obviously, no real process is reversible but you can approximate a reversible process by doing it as slowly as possible. Consider the work done by a gas expanding inside a piston. Initially, assume that the internal and external pressures are the ...