## Search found 49 matches

- Sat Mar 14, 2020 8:43 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: a review problem->where in the book? [ENDORSED]
- Replies:
**1** - Views:
**116**

### a review problem->where in the book? [ENDORSED]

Where is the equation/background for the solution to this problem discussed in the textbook? I'm a little confused by it and I think reading a few paragraphs about this topic would help clear things up "In the above question, the partial pressure of the product is doubled, obviously the above r...

- Sat Mar 14, 2020 8:24 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: are there standard rates of formation?
- Replies:
**4** - Views:
**116**

### are there standard rates of formation?

For H, S, and G, we used standard values of formation for different compounds at particular temperatures and pressures. Does anything similar apply to rates? For example, it takes this long to form 1 mol of H2 from 2 mol of H under standard conditions, and then you can use that value in conjunction ...

- Sat Mar 14, 2020 8:15 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: holding pressure/volume constant
- Replies:
**3** - Views:
**202**

### holding pressure/volume constant

I've generally noticed that we tend to alternately hold either pressure of volume constant for certain situations in thermodynamics, and I am wondering what the benefits are to each and what different ways that might be accomplished in a field setting. So much of what we learn is lab-based, but how ...

- Sat Mar 14, 2020 8:10 pm
- Forum: General Rate Laws
- Topic: rate in an uncontrolled solution
- Replies:
**2** - Views:
**199**

### rate in an uncontrolled solution

What would one need to consider differently when determining the rate of a reaction in an uncontrolled system like a pond, in which there may be many, many different types of molecules affecting the species in your reaction? How would that be handled experimentally?

- Sat Mar 14, 2020 8:05 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: G at different stages of a run
- Replies:
**1** - Views:
**100**

### G at different stages of a run

"The value of DG at a particular stage of the reaction is the difference in the molar Gibbs free energies of the products and the reactants at the partial pressures or concentrations that they have at that stage, weighted by the stoichiometric coefficients interpreted as amounts in moles" ...

- Sat Mar 14, 2020 6:25 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: self-test explanation
- Replies:
**1** - Views:
**79**

### self-test explanation

Self-test 4J.1A Can a nonspontaneous process with a negative DS become spontaneous if the temperature is increased (assuming that DH and DS are both independent of temperature)? [Answer: No]

Why is the answer no? I thought it would be yes since T is multiplied by DS

Why is the answer no? I thought it would be yes since T is multiplied by DS

- Sat Mar 14, 2020 6:16 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: irreversible expansion of ideal gas
- Replies:
**3** - Views:
**149**

### irreversible expansion of ideal gas

Why is w=0 for this? the example on p. 326 uses this to show that the entropy change of the surroundings is 0, which doesn't make a lot of sense to me on a conceptual level.

- Sat Mar 14, 2020 6:10 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: Clausius Inequality [ENDORSED]
- Replies:
**1** - Views:
**111**

### Clausius Inequality [ENDORSED]

"If qrev in the definition of entropy DS = q(rev)/T is replaced by the smaller quantity q(irrev), then DS = q(irrev)/T. In general, the Clausius inequality is DS >= q/T with the equality applicable to a reversible process." Why is this applicable to a reversible process if we are using the...

- Sat Mar 14, 2020 5:54 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: Entropy and complexity
- Replies:
**2** - Views:
**116**

### Entropy and complexity

Why do larger, more complex molecules have greater standard entropies than small, simple ones? Mass and standard entropies are inversely related? Which one weighs out over the other?

- Tue Mar 10, 2020 11:25 pm
- Topic: predicting entropy
- Replies:
**3** - Views:
**119**

### predicting entropy

4G.3 Which would you expect to have a higher molar entropy at T=0, single crystals of BF3 or COF2? Why? The answer given in the solutions manual says that COF2 is the right answer because it is asymmetrical, with an O and two F instead of three F. I also said it was COF2, but I said that it was beca...

- Tue Mar 10, 2020 10:55 pm
- Topic: residual entropy interpretation
- Replies:
**2** - Views:
**126**

### residual entropy interpretation

"When the entropy of 1.00 mol CO(s) is actually measured at temperatures close to T = 0 (by using the technique in Topic 4G), the value found is 4.6 J/K. This value—which is called the residual entropy of the sample, the entropy of a sample at T = 0 arising from positional disorder surviving at...

- Tue Mar 10, 2020 10:30 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: q vs delta H to calculate delta S
- Replies:
**2** - Views:
**114**

### q vs delta H to calculate delta S

4F.1 A human body generates heat at the rate of about 100. W (1 W 5 1 J?s21). (a) At what rate does your body heat generate entropy in your surroundings, taken to be at 20. 8C? (b) How much entropy do you generate each day? (c) Would the entropy generated be greater or less if you were in a room kep...

- Tue Mar 10, 2020 10:09 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: memorizing acids?
- Replies:
**4** - Views:
**204**

### memorizing acids?

This should be in the acid/base section, but my laptop is only giving me the equilibrium section followed immediately by thermodynamics in the Chem 14B menu. Sorry! In the review session this morning, one of the questions listed 4 acids by name and then asked which one had the most protons. It has b...

- Tue Mar 10, 2020 9:46 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: when to use a different C
- Replies:
**2** - Views:
**116**

### when to use a different C

4F.7 Assuming that the heat capacity of an ideal gas is independent of temperature, calculate the entropy change associated with raising the temperature of 1.00 mol of ideal gas atoms reversibly from 37.6 8C to 157.9 8C at (a) constant pressure and (b) constant volume. the solution manual wants me t...

- Tue Mar 10, 2020 9:19 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: when doesn't a solid's temp change?
- Replies:
**3** - Views:
**157**

### when doesn't a solid's temp change?

4F.3 (a) Calculate the change in entropy of a block of copper at 25 8C that absorbs 65 J of energy from a heater. (b) If the block of copper is at 100. 8C and it absorbs 65 J of energy from the heater, what is its entropy change? (c) Explain any difference in entropy change. I understand how the boo...

- Tue Mar 10, 2020 2:23 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Temp and reversibility
- Replies:
**1** - Views:
**85**

### Temp and reversibility

In section 4F.4 of textbook, the "how is that done?" section reads: "To calculate the entropy change in a system due to a temperature change, first note that Eq. 1 itself applies only when the temperature remains constant as heat is supplied to a system.--->Except in special cases, th...

- Mon Mar 09, 2020 11:41 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: predicting solubility
- Replies:
**3** - Views:
**87**

### predicting solubility

One of the learning outcomes is "Use equilibrium constants to predict solubility." I know from my previous chem experience that the solubility of one particle can be affected by the concentrations of other solutes in the solution. If the equilibrium constant is directly related to solubili...

- Mon Mar 09, 2020 11:36 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: cubic equations, assumption
- Replies:
**3** - Views:
**127**

### cubic equations, assumption

Will we ever be in a position where the negligible x assumption in a cubic equation in a K calculation isn't appropriate? If so, how do we solve for x without a graphing calculator?

- Mon Mar 09, 2020 11:32 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding a Catalyst
- Replies:
**6** - Views:
**175**

### Adding a Catalyst

How does adding a catalyst affect the equilibrium concentrations? A catalyst speeds up a reaction's rate, so I thought that a catalyst would favor the products, but 5.33 says that it doesn't have an effect on the eq concentrations. 5.33 Dissociation of a diatomic molecule, X2(g) -> 2 X(g) occurs at ...

- Sun Mar 08, 2020 11:47 pm
- Forum: General Rate Laws
- Topic: 7A.1
- Replies:
**3** - Views:
**57**

### 7A.1

7A.1 Complete the following statements relating to the production of ammonia by the Haber process, for which the overall reac- tion is N2(g) 1 3 H2(g) S 2 NH3(g). (a) The rate of consumption of N2 is ______________ times the rate of consumption of H2. (b) The rate of formation of NH3 is ____________...

- Sun Mar 08, 2020 11:43 pm
- Forum: Second Order Reactions
- Topic: half-life for second order runs
- Replies:
**2** - Views:
**94**

### half-life for second order runs

A half life is the time it takes for the reactant concentration to decrease by half, but how does that work when the stoichiometric coefficients of a chemical equation are not all 1? Does each reactant get a separate half-life, or is the concentration of all the reactants to be summed for an overall...

- Sun Mar 08, 2020 11:41 pm
- Forum: First Order Reactions
- Topic: equation derivations
- Replies:
**9** - Views:
**204**

### equation derivations

Are we ever going to be asked to replicate the derivation of an equation on an exam? Some of the derivations in this section were confusing, and if I can just memorize the equation I need and get full points, it would be really helpful for me.

- Sun Mar 08, 2020 11:41 pm
- Forum: First Order Reactions
- Topic: equation derivations
- Replies:
**5** - Views:
**67**

### equation derivations

Are we ever going to be asked to replicate the derivation of an equation on an exam? Some of the derivations in this section were confusing, and if I can just memorize the equation I need and get full points, it would be really helpful for me.

- Sun Mar 08, 2020 11:38 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Molecularity
- Replies:
**4** - Views:
**87**

### Molecularity

I'm a little confused on the definition of molecularity. Or I suppose, the definition of "species" Is a species a single molecule, or is it a single type of molecule? I may be confused because in biology, a species is a type of organism, but this definition seems to have little to do with ...

- Sun Feb 23, 2020 6:10 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Units for delta G calculations w/E
- Replies:
**1** - Views:
**32**

### Units for delta G calculations w/E

The units listed in the solutions manual for the delta G under standard conditions is kj/mol, and I am confused as to where the /mol comes from.

The equation is G=-nFE, and n is the number of moles, so shouldn't that cancel with the /mol in the unit of Faraday's constant?

The equation is G=-nFE, and n is the number of moles, so shouldn't that cancel with the /mol in the unit of Faraday's constant?

- Sun Feb 23, 2020 5:59 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagram, what to include
- Replies:
**3** - Views:
**92**

### Cell Diagram, what to include

For the rxn 2No3- + 8H+ + 6Hg(l) -> 3Hg2^2+ + 2NO(g) + 4H20(l), the cell diagram given by the solutions manual was Hg|Hg2^2+||No3-, H+|NO(g)|Pt(s) I'm confused about the right hand side of the cell diagram. Why is Hydrogen included? Why are there three separate sections? How do I tell that I should ...

- Sun Feb 23, 2020 5:08 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Solution Manual Error??
- Replies:
**1** - Views:
**59**

### Solution Manual Error??

6M.1 "A student was given a standard Cu(s)|Cu^2+(aq) half-cell and another half-cell containing unknown metal M in 1.00M M(NO3)2 and formed the cell M(S)|M+||Cu2+|Cu(s). The cell potential was found to be -.689V. What is the standard potential of (M^2+/M)?" The solution manual rewrites the...

- Sun Feb 16, 2020 11:51 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic conditions- relevant?
- Replies:
**1** - Views:
**38**

### Acidic conditions- relevant?

We are frequently given the condition "under acidic conditions" to let us know that hydrogen ions aren't a limiting reactant, but will we ever be in a situation in which they will be limiting? In that case, would it be appropriate to use an ice box to figure out the initial H ion concentra...

- Sun Feb 16, 2020 11:46 pm
- Forum: Balancing Redox Reactions
- Topic: Possibly helpful: LEO the lion goes GER
- Replies:
**2** - Views:
**202**

### Possibly helpful: LEO the lion goes GER

In high school, I learned to use Leo the lion like Dr. Lavelle said during lecture, but my teacher included an acronym to remember reduction as well, making the entire phrase "Leo the lion goes ger" with GER standing for Gain of Electrons is Reduction. I don't know if it was just Dr. Lavel...

- Sun Feb 16, 2020 11:42 pm
- Forum: Balancing Redox Reactions
- Topic: Odd number of electrons
- Replies:
**3** - Views:
**112**

### Odd number of electrons

On a practice problem for balancing redox reactions, I found that one compound is gaining three electrons, but there were only two atoms of the same element within that compound that were able to accept electrons. I had made a mistake and figured out what I did wrong using the solutions manual, but ...

- Sun Feb 16, 2020 11:38 pm
- Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
- Topic: Light bulbs? [ENDORSED]
- Replies:
**1** - Views:
**58**

### Light bulbs? [ENDORSED]

How do light bulbs work? I know that photons are emitted when an electron is excited to a higher energy level and then drops back, but if electricity is just a flow of electrons, how does that make electrons in the light bulb do this? Also, where do the electrons that are making this happen go?

- Sun Feb 16, 2020 11:36 pm
- Forum: Balancing Redox Reactions
- Topic: Electron transfer and entropy
- Replies:
**1** - Views:
**41**

### Electron transfer and entropy

How does the transfer of electrons affect a reactions change in entropy? Like, does an electron being transferred from an element with low electronegativity to high electronegativity decrease the amount of disorder in the system since the electronegative atom will hold more "tightly" to th...

- Sun Feb 16, 2020 11:32 pm
- Forum: Balancing Redox Reactions
- Topic: Assuming Oxidation Number
- Replies:
**1** - Views:
**17**

### Assuming Oxidation Number

In high school, I was taught to always assume that oxygen has an oxidation number of -2 and that hydrogen has an oxidation number of +1. Is it safe for me to continue making that assumption in this course?

- Tue Feb 11, 2020 11:46 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Why is delta U a state function?
- Replies:
**4** - Views:
**99**

### Why is delta U a state function?

Conceptually, I understand how the internal energy of a system is not dependent upon the path taken to get to that state. But work and heat are not state functions, and so it's hard for me to wrap my head around two non-state functions being able to combine to make a state function. The other state ...

- Sun Feb 09, 2020 11:36 pm
- Topic: Qualitative Entropy of Diatomic Gases
- Replies:
**1** - Views:
**27**

### Qualitative Entropy of Diatomic Gases

"Which would you expect have a higher standard molar entropy at 298K? a) Iodine vapor or bromine vapor" Both of these elements are diatomic, and since they're both in the same state and it is asking about standard molar entropy, the only difference between them is their molar mass. What ef...

- Sun Feb 09, 2020 11:26 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Nonexpansion work
- Replies:
**1** - Views:
**48**

### Nonexpansion work

"The change in Gibbs free energy for a process is also a measure of the maximum nonexpansion work that the system can do at constant temperature and pressure" What work can a chemical system do other than expansion? Is this aspect of the definition of Gibbs free energy going to be relevant...

- Sun Feb 09, 2020 11:20 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Vaporization of water below 100C?
- Replies:
**1** - Views:
**57**

### Vaporization of water below 100C?

"Calculate the standard entropy of the vaporization of water at 85 degrees C, given that its standard entropy of vaporization at 100 degrees C is 109.0 J/K/mol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/K/mol and 33.6 J/K/mol, respectively, in ...

- Sun Feb 09, 2020 11:12 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Pistons and Reversibility
- Replies:
**1** - Views:
**45**

### Pistons and Reversibility

In the sixth edition of the textbook, one of the practice problems describes a situation in which a gas is compressed with a piston, but says that this compression is irreversible, and asks to calculate the entropy. This question confuses me for two different reasons, 1) isn't entropy a state functi...

- Sun Feb 09, 2020 11:08 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Reversible or Irreversible
- Replies:
**1** - Views:
**28**

### Re: Reversible or Irreversible

This should have been in the entropy section, sorry!

- Sun Feb 09, 2020 11:04 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Reversible or Irreversible
- Replies:
**1** - Views:
**28**

### Reversible or Irreversible

I have the last edition of the textbook, and one of the questions describes a situation in which 40.0 heat energy is transferred from a large reservoir at 800.K to one at 200.K. It then asks for the entropy change. With so little detail provided, how can I tell if this heat transfer is reversible or...

- Sun Feb 09, 2020 11:00 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Reversibility and Entropy [ENDORSED]
- Replies:
**2** - Views:
**151**

### Reversibility and Entropy [ENDORSED]

In the lecture, Prof Lavelle said that since entropy is a state function, the reversibility of a reaction doesn't matter in calculating delta S. I am a little confused about this, since we also know that entropy increases with the number of possible states, and the components of reversible reaction ...

- Mon Feb 03, 2020 12:00 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Double bonds
- Replies:
**4** - Views:
**68**

### Double bonds

I am a little bit confused about what to do when only one bond within a double bond is broken. I'm using the value listed in the table, but I am not getting the right answer. I am using the same method as with the other problems, and the only difference I can tell is that there is a double bond invo...

- Sun Feb 02, 2020 11:57 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: taking phase change into account
- Replies:
**5** - Views:
**65**

### taking phase change into account

I am a little bit confused about when the phase change needs to be taken into account in enthalpy change calculations. I have written in my notes that it is only necessary to include the phase change when there are gases involved. Why is this the case?

- Sun Feb 02, 2020 11:54 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Sig figs and calorimetry example
- Replies:
**2** - Views:
**33**

### Sig figs and calorimetry example

On last Monday's lecture, Prof Lavelle did a problem solving calorimetry example, and I am confused about the way that the significant figures were calculated. The given temperatures were 25 and 31.9 degrees Celsius, and the delta T calculated was 6.9 degrees, but. it was my understanding that sig f...

- Sat Jan 25, 2020 11:58 pm
- Forum: Phase Changes & Related Calculations
- Topic: sublimation???
- Replies:
**1** - Views:
**30**

### sublimation???

can the delta h of sublimation be calculated by adding the delta h of melting with the delta h of vaporization? Or does it take a totally separate path? But because delta H is a state function, shouldn't it be the case that sublimation's enthalpy change is the same as the enthalpy change of melting ...

- Sat Jan 25, 2020 11:55 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Constant Pressure and how you get it in a calorimeter
- Replies:
**3** - Views:
**73**

### Constant Pressure and how you get it in a calorimeter

In the lecture where this was discussed, Dr. Lavelle said that delta h was equal to q at a constant pressure. When he was talking about this with an open vessel, I understood how that was possible, but aren't calorimeters sealed? If their volume can't change, then how do they maintain a constant pre...

- Sat Jan 25, 2020 11:53 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Negative Square Root solving an ICE box
- Replies:
**13** - Views:
**114**

### Negative Square Root solving an ICE box

While trying to solve an ICE box, I was using the quadratic formula and got a negative number inside of the square root term. What am I supposed to do with this? Is it supposed to be possible, or have I definitely made a mistake elsewhere?

- Sat Jan 25, 2020 9:06 pm
- Forum: Phase Changes & Related Calculations
- Topic: Bond Enthalpies with State Changes
- Replies:
**4** - Views:
**47**

### Bond Enthalpies with State Changes

I am a little bit confused as to when I should include phase change enthalpies in my delta H calculations. From the lecture, I would think that it is only included when the state change involves a gas, and not when it is between a liquid and a solid. This doesn't make sense to me, so I'm wondering i...

- Thu Jan 23, 2020 12:32 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: State Properties and q vs H
- Replies:
**2** - Views:
**60**

### State Properties and q vs H

From my understanding of the lecture yesterday, delta H and q are equal to one another in an open vessel, so why is delta H a state property but q isn't? Shouldn't the heat also not depend on the path that was taken to get to that heat? If it is 50 degrees outside, it is 50 regardless of yesterday's...