Linked Questions

8
votes
2answers
18k views

What is the difference between ΔG and ΔG “with an o on top”? [duplicate]

What is the difference between $\Delta G$ and $\Delta G^\circ$? I couldn't figure it out. Ex: $\Delta G^\circ = -RT\ln K$ $\Delta G = \Delta G^\circ + RT \ln Q$ What is the difference, is it that $\...
25
votes
1answer
33k views

Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

The reaction of one equivalent of hydrogen bromide with 1,3-butadiene gives different products at under different conditions:1 The addition of hydrogen chloride also gives rise to similar products.2 ...
12
votes
1answer
36k views

Derivation of van 't Hoff equation for temperature dependence of equilibrium constant

While I was reading about the usefulness of the quantity $\Delta H$, I found that it can be used to calculate the how the equilibrium constant varies with temperature. How can this be done? Does it ...
11
votes
2answers
5k views

Is the Gibbs standard free energy always constant?

I am a biochemistry student and we are learning about thermodynamics. Is the Gibbs standard free energy for a reaction always constant? The equation below suggests that it changes with temperature: $$...
11
votes
3answers
4k views

What is the difference between ΔG and ΔrG?

Consider the reaction $$\ce{A -> B}$$ The reaction Gibbs free energy, $\Delta_\mathrm{r} G$ is given by the following equation $$\Delta_\mathrm{r} G = \Delta_\mathrm{r} G^\circ + RT \ln Q$$ Now ...
4
votes
3answers
635 views

If change in free energy (G) is positive, how do those reactions still occur?

I was doing a couple of problems for homework: Calculate $K_\mathrm{sp}$ of $\ce{AgI}$ at $55.0\ \mathrm{^\circ C}$ Calculate $K_\mathrm{b}$ of $\ce{NH3}$ at $36.0\ \mathrm{^\circ C}$ I have to use ...
6
votes
3answers
488 views

Calculating ΔG at the extremes of reaction extent

This question follows on from a great post on comparing $\Delta_\mathrm{r} G^{\circ}$ to $\Delta_\mathrm{r} G$ answered here The G vs ξ graph that is used in the answer is an excellent tool to ...
4
votes
2answers
380 views

Change in standard Gibbs energy is always zero?

So I have this statement from our professor : We have $\Delta G^\circ = -RT\ln K$ and under standard conditions the activities of all substances in the reaction is $1$ ($a=1$), therefore $\Delta G^\...
2
votes
2answers
1k views

Gibbs free energy in standard state vs. equilibrium

I have a problem with the definition of the standard Gibbs energy and its connection to the equilibrium constants. I think, that I've basically understood what the different equation mean but there ...
4
votes
1answer
800 views

Do I use the Nernst equation when the concentrations of electrolyte in both half cells are equal?

I'm doing a chemistry report, and for my experiment I investigated the amount of voltage produced by different half cells in a voltaic cell. However, I tested them under nonstandard conditions as ...
0
votes
1answer
3k views

Temperature in the Gibbs Free Energy equation

My professor gave us 2 different ways to calculate this problem. I did it using the Clausis-Clapeyron equation. However, I don't quite get the second method because I thought that if the change in ...
4
votes
2answers
367 views

How come ∆G ≤ 0 is used for spontaneity in electrochemistry, not ∆G ≤ W(other)?

The spontaneity condition for a system at constant temperature and pressure in which the only type of work accomplished is of the $pV$ type can be expressed as: $$\Delta G\le0\tag1$$ In case of ...
2
votes
1answer
305 views

Gibbs Free Energy Notation

What's the difference between $G$, $\Delta G$, $\Delta G^\circ$, and $\Delta_\mathrm r G^\circ$? I've seen the first two used interchangably, and seen $G$ specifically referred to as change in Gibbs ...
-2
votes
1answer
421 views

What does “heat is evolved at standard-state conditions” mean?

When $\pu{0.539 g}$ of $\ce{Na(s)}$ reacts with excess $\ce{F2(g)}$ to form $\ce{NaF(s)}$, $\pu{13.3 kJ}$ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation ($\...
2
votes
1answer
95 views

Discrepancies in calculating free energy values listed in Stumm and Morgan

I am hoping someone can help me with a clarifying a calculation on a fundamental thermodynamic understanding of reactions. Below is Table 2.5 from Stumm and Morgan's Aquatic Chemistry. Table 2.5. ...

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