CHEMISTRY COMMUNITY

OliviaShearin2E

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 ...

OliviaShearin2E

Is there a lecture on Friday?

OliviaShearin2E

I believe the catalyst also does not appear in the overall reaction (though it may appear in the rate law).

OliviaShearin2E

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...

OliviaShearin2E

Eli is right, I would disregard the last reply as I believe the species will always be solid or aqueous.

OliviaShearin2E

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...

OliviaShearin2E

Yup, it's definitely a typo. When I searched old chem community problems I found the same discussion.

OliviaShearin2E

I would expect everything before problem 15.45 to be covered.

OliviaShearin2E

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.

OliviaShearin2E

Johann is right but to be clearer, first order in B means that the rate is proportional to $[B]^{1}$ , second order in B means that the rate is proportional to $[B]^{2}$ . and third order in B means that the rate is proportional to $[B]^{3}$ .

OliviaShearin2E

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...

OliviaShearin2E

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.

OliviaShearin2E

The oxidation state of any element in its most stable form is 0.

OliviaShearin2E

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.

OliviaShearin2E

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 ...

OliviaShearin2E

Enthalpy is a state function.

OliviaShearin2E

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...

OliviaShearin2E

The formula sheet online uses 273.15 so I would stick with that.

OliviaShearin2E

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.

OliviaShearin2E

Can someone clarify what types of work? Some sites say maximum reversible work and others say maximum nonexpansion work.

OliviaShearin2E

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?

OliviaShearin2E

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...

OliviaShearin2E

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.

OliviaShearin2E

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.

OliviaShearin2E

Can you further clarify your question?

OliviaShearin2E

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.

OliviaShearin2E

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!

OliviaShearin2E

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...

OliviaShearin2E

Does this basically mean the reaction takes place at a constant temperature?

OliviaShearin2E

\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. ...

OliviaShearin2E

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.

OliviaShearin2E

(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...

OliviaShearin2E

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...

OliviaShearin2E

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...

OliviaShearin2E

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 ...

OliviaShearin2E

I will attach my work to the post, hope it helps!

OliviaShearin2E

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 ...

CHEMISTRY COMMUNITY

Search found 37 matches

Re: total entropy of the system

Lecture Friday

Re: Distinguishing a Catalyst

Re: Given information

Re: Cell Diagram

Re: 15.27

Re: Homework Problem 15.19C

Re: Test 3

Re: K0 vs K1

Re: 15.17

15.105

Re: #15.19-rate constant

Re: Oxidation states

Re: Inert Electrode

Re: Galvanic Cells vs Electrochemical Cells

Re: Is enthalpy a state function?

Re: Homework Q14.117

Re: Using Kelvin [ENDORSED]

Re: Reversible

Re: Maximum Energy Able to Do Work [ENDORSED]

O2 Microstates

Re: Tendency of processes

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

Ozone oxidation number

Re: Gibbs Free Energy [ENDORSED]

Re: 9.13

Re: Gibbs free energy equations

Gibbs free energy equations

Re: Confusion about entropy formula

Confusion about entropy formula

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

Homework 8.93b

8.91

Most Stable Forms

Re: Energy and Phase Changes

Re: Homework Question 8.3

8.3 Reversible Isothermal Expansion