# Tag Info

Accepted

### What is the difference between ∆G and ∆G°?

Short answer Does it need to be at $25~^\circ\mathrm{C}$? No. $\Delta_\mathrm{r} G^\circ$ can be defined at any temperature you wish to define it at, since the standard state does not ...
Accepted

### Which equilibrium constant is appropriate to use?

As noted in this previous question, the correct definition of the equilibrium constant $K$ depends on activities. If you are interested in the derivation of the equation $\Delta G^\circ = -RT \ln K$ (...

### Can single molecules of C and O2 react in isolation, and if so how will momentum be conserved?

$\ce{C + O2}$ is awfully complicated, so let's just pretend you've asked this: In a single act of the reaction $\ce{H. + H .-> H2}$, how is momentum conserved? That's a legitimate concern all right....

### Why is entropy favorable?

Thermodynamics. The second law of thermodynamics states that entropy always increases in an isolated system. This is taken as a fundamental postulate---we simply accept this statement as a fact ...
Accepted

### What is the difference between ΔG and ΔrG?

Not for the faint-hearted: There is an excellent, but very mathsy, article here: J. Chem. Educ. 2014, 91, 386 describing the difference. The Gibbs free energy change, $\Delta G$ You are quite right ...
Accepted

### Why proton concentration is divided by 10⁻⁷?

The textbook is precisely correct. The equilibrium constant $K$ which the logarithm is taken of is dimensionless, and includes activities or fugacities, and not concentrations and pressures. In ...
Accepted

### Why would there be a non-zero Gibbs energy of mixing for ideal gases?

When we talk about mixing, we usually mean that two components are in different parts of a container before mixing and then they share the entire container after mixing. In other words, the total ...
Accepted

### Is there a way to experimentally measure entropy?

The most common way of measuring $\Delta S^\circ$ for a chemical reaction is probably by making a van't Hoff plot. You measure the equilibrium constant $K$ at different temperatures and plot $\ln K$ ...
Accepted

### Why is entropy favorable?

It appears you're looking for an ELI5-style answer, not an elaborate definition. Entropy just happens – as long as the universe isn't frozen solid, things will always be moving around, and that ...
Accepted

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

$\Delta G^\circ_m$ is the difference in molar Gibbs free energy between the reagents and products in their standard states (in the case of $\ce{AgI(s)}$, the standard state for the reagent is the pure ...

### Why exactly are standard potentials additive?

Following on Derek's great answer, it is very important to remind that the conventional way we use to add half-cell potentials is a consequence of the conservation of energy. Therefore, we should look ...

### True or false: "If a reaction has a large negative value of ∆G, then it will be a fast reaction."

There is the Bell–Evans–Polanyi principle stating that "the difference in activation energy between two reactions of the same family is proportional to the difference of their enthalpy of ...

### Why is entropy favorable?

Do not think of entropy as 'disorder' as this is misleading, better is that it is a 'measure of disorder' but this is equally vague. It is better to think of entropy as the number of ways that '...

### When is a reaction reversible?

"Reversible" is not binary. Both the forward and backward reactions always occur and the equilibrium system never has zero reactants or zero products. Thus, irreversible reactions are called this ...

### What is the difference between ∆G and ∆G°?

I think the answer to these questions can be simplified considerably. My answer would start out with the part of orthocresol's answer which says: What exactly, then, is $\Delta G^\circ$? The truth ...

### Why at constant pressure and temperature Gibbs energy change of a process can be negative?

The relation $$\mathrm dG = V\,\mathrm dp - S\,\mathrm dT\tag{1}$$ implies that the Gibbs free energy of the system depends only on the two variables $T$ and $p$, e.g., as in the case of a single-...

### Why would there be a non-zero Gibbs energy of mixing for ideal gases?

With your reply you seem to have answered part of your question. I would like to add a bit about the other part. I will have to do it mathematically first, there is no other shortcut, but then we will ...
Accepted

### Why can't a reaction go to completion?

You alluded to the answer when you mention activation energy. Kinetically the equilibrium constant is $K_e = k_f/k_b$ where $k_f$ and $k_b$ are the forward are reverse reaction rate constants in the ...

### How to estimate the temperature needed to overcome an activation energy barrier?

You could convert the rate constant($k$) to half-life($t_{1/2}$) which would give you an idea of the time scale required for the reaction to finish at a certain temperature. The equation to obtain ...

### How to estimate the temperature needed to overcome an activation energy barrier?

From the Eyring equation, we can simply calculate the $k$ value for it. \begin{align} k &= \frac{k_\mathrm{b} T}{h}\exp\left(\frac{-\Delta G^\ddagger}{RT}\right)\\ k_\mathrm{b} &= \pu{1.38E-9 ...

### Is there a reason for the mathematical form of the equilibrium constant?

I will make "the proof" mentioned by Silvio Levy. Let's consider a chemical reaction, written as: $$\sum_{i} \nu_i \ce{A}_i \longrightarrow 0$$ where $\nu_i$ are the stoichiometric coefficients of ...
Accepted

### What is the difference between ∆G and ∆G°?

I see it in different way. You are right in most textbooks $\Delta G^0$ means free energy change at $25~\mathrm{^\circ C}$ but in this case you have to think in a different way. I see it as ...

### Is there a way to experimentally measure entropy?

The entropy change between two thermodynamic equilibrium states of a system can definitely be directly measured experimentally. To do so, one needs to devise (dream up) a reversible path between the ...
The fundamental relation for an Ideal Gas, in the entropy representation is S(U,V,N) = NS_0 + NR\ln\left[ \left( \frac{U}{U_0} \right)^c \left( \frac{V}{V_0} \right) ...