Search found 37 matches

by OliviaShearin2E
Sat Mar 17, 2018 10:57 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: total entropy of the system
Replies: 3
Views: 224

Re: total entropy of the system

The second law does not mean that entropy always increases, but that entropy can never decrease. If total entropy is negative, the reaction is not spontaneous as you said. This means the reverse reaction is spontaneous so the total entropy increases. When the reaction is at equilibrium, the entropy ...
by OliviaShearin2E
Tue Mar 13, 2018 6:06 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Friday
Replies: 4
Views: 311

Lecture Friday

Is there a lecture on Friday?
by OliviaShearin2E
Mon Mar 12, 2018 9:56 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Distinguishing a Catalyst
Replies: 4
Views: 184

Re: Distinguishing a Catalyst

I believe the catalyst also does not appear in the overall reaction (though it may appear in the rate law).
by OliviaShearin2E
Mon Mar 12, 2018 9:55 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Given information
Replies: 5
Views: 215

Re: Given information

I believe he said in class that we would always be given the slow step and the course reader practice finals specify which step is slow as well. Another type of problem is identifying which step would be the slow step based on the rate law, in which case you naturally would not be given this informa...
by OliviaShearin2E
Mon Mar 12, 2018 9:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 163

Re: Cell Diagram

Eli is right, I would disregard the last reply as I believe the species will always be solid or aqueous.
by OliviaShearin2E
Wed Mar 07, 2018 9:11 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.27
Replies: 2
Views: 231

Re: 15.27

Personally (I don't have the solutions manual) I knew that to find t_{1/2} you divide ln 2 by k, so generally you divide ln(reciprocal of the fraction) by k. 15% is equivalent to the fraction 15/100 which equals 3/20, so the reciprocal is 20/3. I found the solution by taking ln(20/3) and dividing by...
by OliviaShearin2E
Wed Mar 07, 2018 9:09 am
Forum: General Rate Laws
Topic: Homework Problem 15.19C
Replies: 5
Views: 204

Re: Homework Problem 15.19C

Yup, it's definitely a typo. When I searched old chem community problems I found the same discussion.
by OliviaShearin2E
Wed Mar 07, 2018 9:08 am
Forum: Student Social/Study Group
Topic: Test 3
Replies: 3
Views: 337

Re: Test 3

I would expect everything before problem 15.45 to be covered.
by OliviaShearin2E
Tue Feb 27, 2018 5:38 pm
Forum: Zero Order Reactions
Topic: K0 vs K1
Replies: 2
Views: 134

Re: K0 vs K1

Can you clarify your question? I am not sure what is meant by k0. For zero order reactions, Rate = k so k is still present.
by OliviaShearin2E
Tue Feb 27, 2018 5:36 pm
Forum: General Rate Laws
Topic: 15.17
Replies: 4
Views: 181

Re: 15.17

Johann is right but to be clearer, first order in B means that the rate is proportional to , second order in B means that the rate is proportional to . and third order in B means that the rate is proportional to .
by OliviaShearin2E
Tue Feb 27, 2018 5:33 pm
Forum: First Order Reactions
Topic: 15.105
Replies: 1
Views: 113

15.105

To prepare a 15-kg dog for surgery, 150 mg of the anesthetic phenobarbitol is administered intravenously. The reaction in which the anesthetic is metabolized (decomposed in the body) is rst order in phenobarbitol and has a half-life of 4.5 h. After about 2 h, the drug begins to lose its effect. Howe...
by OliviaShearin2E
Wed Feb 21, 2018 6:34 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: #15.19-rate constant
Replies: 2
Views: 300

Re: #15.19-rate constant

I dont think chem mod actually looked at your work, you're on the right track but you should be multiplying by 10^-12 instead of 10^-3 because the units are mmol^-4 so you would need to think about that factor of -4 when converting units.
by OliviaShearin2E
Mon Feb 19, 2018 7:32 pm
Forum: Balancing Redox Reactions
Topic: Oxidation states
Replies: 2
Views: 72

Re: Oxidation states

The oxidation state of any element in its most stable form is 0.
by OliviaShearin2E
Mon Feb 19, 2018 7:31 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrode
Replies: 2
Views: 171

Re: Inert Electrode

An inert electrode is needed when the species in the electrode do not conduct electricity, so you would use one in every situation except when the electrode is made of metals that would conduct electricity like transition metals.
by OliviaShearin2E
Mon Feb 19, 2018 7:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells vs Electrochemical Cells
Replies: 4
Views: 145

Re: Galvanic Cells vs Electrochemical Cells

From LibreTexts: "There are two types of electrochemical cells: galvanic cells and electrolytic cells. A galvanic (voltaic) cell uses the energy released during a spontaneous redox reaction (ΔG < 0) to generate electricity. This type of electrochemical cell is often called a voltaic cell after ...
by OliviaShearin2E
Thu Feb 15, 2018 4:30 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Homework Q14.117
Replies: 2
Views: 194

Re: Homework Q14.117

14.117 The body functions as a kind of fuel cell that uses oxygen from the air to oxidize glucose: C_{6}H_{12}O_{6}(aq)+6O_{2}(g)\rightarrow 6CO_{2}(g)+6H_{2}O(l) During normal activity, a person uses the equivalent of about 10 MJ of energy a day. Assume that this val...
by OliviaShearin2E
Wed Feb 14, 2018 1:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Using Kelvin [ENDORSED]
Replies: 3
Views: 161

Re: Using Kelvin [ENDORSED]

The formula sheet online uses 273.15 so I would stick with that.
by OliviaShearin2E
Wed Feb 14, 2018 1:06 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible
Replies: 4
Views: 198

Re: Reversible

As well as what Adrian said, a process can have delta U = 0 even with a temperature change if the system returns to its original state, since U is a state function.
by OliviaShearin2E
Wed Feb 14, 2018 1:04 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Maximum Energy Able to Do Work [ENDORSED]
Replies: 3
Views: 179

Re: Maximum Energy Able to Do Work [ENDORSED]

Can someone clarify what types of work? Some sites say maximum reversible work and others say maximum nonexpansion work.
by OliviaShearin2E
Sat Feb 10, 2018 4:42 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: O2 Microstates
Replies: 2
Views: 218

O2 Microstates

Does someone know why O2 has one microstate (in context of S=Kb lnW) instead of 2? Wouldn't translational motion mean that there would be 2 states (each O2 molecule on the left/ right), or is it different because both O2 molecules are identical?
by OliviaShearin2E
Tue Feb 06, 2018 2:56 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Tendency of processes
Replies: 2
Views: 98

Re: Tendency of processes

Manasa pointed out that a reaction will be spontaneous at low Gibbs energy, but as a whole reactions will proceed until they are at equilibrium where ΔG=0. Since ΔG = ΔGº + RT lnQ and ΔGº= -RT lnK, ΔG=0 when Q=K. Essentially, the reaction tries to minimize its Gibbs free energy as it proceeds toward...
by OliviaShearin2E
Tue Feb 06, 2018 2:48 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Differing Equations Used For delta S with Change in Temperature
Replies: 3
Views: 173

Re: Differing Equations Used For delta S with Change in Temperature

S=nRln(T2/T1) and S=nRln(P1/P2) are for isothermal expansion. S=Cln(T2/T1) is for expansion where temperature changes, but the system is at either constant pressure or volume.
by OliviaShearin2E
Tue Feb 06, 2018 2:41 pm
Forum: Balancing Redox Reactions
Topic: Ozone oxidation number
Replies: 2
Views: 100

Ozone oxidation number

What is the oxidation number of ozone (O3)? I think it's zero but I don't know if this qualifies a stable form of oxygen. I'm asking in context of problem 14.5a.
by OliviaShearin2E
Mon Jan 29, 2018 8:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy [ENDORSED]
Replies: 6
Views: 510

Re: Gibbs Free Energy [ENDORSED]

Can you further clarify your question?
by OliviaShearin2E
Mon Jan 29, 2018 8:24 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 3
Views: 136

Re: 9.13

I can confirm that you get the correct answer from using 1 mol of gas. There are also a few other problems in the homework with this assumption.
by OliviaShearin2E
Mon Jan 29, 2018 8:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy equations
Replies: 4
Views: 170

Re: Gibbs free energy equations

Sorry, is there any way you could clarify what the molar Gibbs free energy is further? I am still slightly confused. Thank you for your response!
by OliviaShearin2E
Mon Jan 22, 2018 10:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy equations
Replies: 4
Views: 170

Gibbs free energy equations

Is there a difference between using standard molar Gibbs energies and standard Gibbs free energies of formation to calculate \Delta G^{\circ} in the equation \Delta G^{\circ} = \Sigma nG_{m}^{\circ}(products)- \Sigma nG_{m}^{\circ}(reactants) (or \Delta G^{\circ} = \Sigma nG_{f}^{\ci...
by OliviaShearin2E
Mon Jan 22, 2018 10:11 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Confusion about entropy formula
Replies: 6
Views: 154

Re: Confusion about entropy formula

Does this basically mean the reaction takes place at a constant temperature?
by OliviaShearin2E
Mon Jan 22, 2018 10:11 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Confusion about entropy formula
Replies: 6
Views: 154

Confusion about entropy formula

\Delta S= q_{rev} / T apparently only works for heat transferred reversibly. How do we know when the situation has heat transferred reversibly, and what exactly does this mean? Quite a few of the homeworks so far have used this equation but there is no specification on the method of heat transfer. ...
by OliviaShearin2E
Wed Jan 17, 2018 2:59 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Is there a way specific way to approach into seeing if open closed or isolated?
Replies: 9
Views: 335

Re: Is there a way specific way to approach into seeing if open closed or isolated?

To elaborate on what Ryan said, a closed system allows the movement of energy but not mass. An open system allows the movement of energy and mass.
by OliviaShearin2E
Wed Jan 17, 2018 2:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework 8.93b
Replies: 1
Views: 82

Homework 8.93b

(a) Calculate the work that must be done against the atmosphere for the expansion of the gaseous products in the combustion of 1.00 mol C6H6(l) at 25 C and 1.00 bar. (b) Using data in Appendix 2A, calculate the standard enthalpy of the reaction. (c) Calculate the change in internal energy, U , of th...
by OliviaShearin2E
Wed Jan 17, 2018 2:46 pm
Forum: Phase Changes & Related Calculations
Topic: 8.91
Replies: 1
Views: 93

8.91

Can someone show their work for problem 8.91 in the homework? I don't understand how to relate rate of time to the other side of the equation. I figured: rate of heat transfer x time = heat to melt the ice + heat to change the temperature of the water to 5ºC And that rate of heat transfer is connect...
by OliviaShearin2E
Thu Jan 11, 2018 1:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Most Stable Forms
Replies: 4
Views: 212

Most Stable Forms

How do we know the most stable form of an element, such that standard enthalpy of formation would be zero for that element? For instance, I would assume the most stable form of water would be H2O(l) because it is found in most commonly in nature, but its enthalpy of formation is -285.83. Is the most...
by OliviaShearin2E
Wed Jan 10, 2018 3:21 pm
Forum: Phase Changes & Related Calculations
Topic: Energy and Phase Changes
Replies: 5
Views: 248

Re: Energy and Phase Changes

I agree with Justin and Tatiana. I found this description on Quora to summarize: "In ice, water molecules are very closely packed together; the intermolecular forces of attraction are particularly strong in solids, which means that the molecules have little to no freedom to move. When you heat ...
by OliviaShearin2E
Wed Jan 10, 2018 3:16 pm
Forum: Calculating Work of Expansion
Topic: Homework Question 8.3
Replies: 4
Views: 234

Re: Homework Question 8.3

I will attach my work to the post, hope it helps!
IMG_4013.jpg
by OliviaShearin2E
Mon Jan 08, 2018 4:04 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.3 Reversible Isothermal Expansion
Replies: 3
Views: 230

8.3 Reversible Isothermal Expansion

8.3 describes, "In an isothermal expansion, the pressure of the gas falls as it expands (by Boyle’s law); so, to achieve reversible expansion, the external pressure must be reduced in step with the change in volume so that at every stage the external pressure is the same as the pressure of the ...

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