57 votes
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What would be the effect of the addition of an inert gas to a reaction at equilibrium?

Dissociation obviously increases the number of moles. The addition of an inert gas can affect the equilbrium, but only if the volume is allowed to change. There are two cases on which equilibrium ...
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Why don't everyday things burn?

The equilibrium constant for combustion of organic matter in air with oxygen is not small, but extremely large ($K_\mathrm{eq} \gg 1$), as is expected from a reaction that is simultaneously very ...
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53 votes
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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 ...
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44 votes

What would be the effect of the addition of an inert gas to a reaction at equilibrium?

Nick's answer is good. Let's add a little maths. Let's take an example dissociation reaction $\ce{A<=>B + C}$ for which $K_p=1$. Since $$K_p = \frac{P_B P_C}{P_A}$$ one equilibrium scenario ...
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30 votes
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Won't the net effect of a catalyst be zero if it creates a new path with lower activation energy?

Your realisation is correct and something chemistry teachers try to hammer into their students’ heads time and time again (and yet, the point is still often lost): Catalysts will never change the ...
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25 votes
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How does a chemical "know" which other species are present and where equilibrium is?

What we got here is a dynamic equilibrium, not a static one. For a static one the molecules would need to know when to stop reacting or when to react in a certain way, in a dynamic equilibrium you don'...
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24 votes
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Is there a difference between equilibrium and steady state?

Yes, equilibrium and steady-state are distinct concepts. A reaction is at equilibrium if reactants and products are both present, the forward and reverse rates are equal and the concentrations don't ...
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23 votes
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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 $\Delta G^\circ = -RT \ln K$ (...
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20 votes

In a saturated solution, why is there ongoing dissolution and crystallisation?

Because equilibrium is dynamic not static There are many things in the world of chemistry which could be simpler but are not. Equilibrium is one of them. There are few chemical processes where ...
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19 votes
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Is every chemical reaction in equilibrium?

Yes, every chemical reaction can theoretically be in equilibrium. Every reaction is reversible. See my answer to chem.SE question 43258 for more details. This includes even precipitation reactions ...
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19 votes
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I'm pretty sure this doesn't follow Le Chatelier's Principle

Le Chatelier's Principle does not directly say what happens to concentration ratios. Nor does it directly compare conditions after a disturbance with those before. It says what happens only after a ...
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19 votes

What does “to the left” mean?

Yes, "to the left" refers to the left side of an equilibrium expression. Traditionally, the autoionization of water is written as $$\ce{2H2O <=> H3O+ + OH-}$$ When we talk about equilibrium ...
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18 votes
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Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

It very much depends on what definition of the equilibrium constant you are looking. The most common usage of the same has quite a variety of possible setups, see goldbook: Equilibrium Constant ...
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Why is chromate stable in basic medium and dichromate stable in acidic medium?

I will be using an approach which has been enlisted in the following book for answering this question: Arrow Pushing in Inorganic Chemistry ;A Logical Approach to the Chemistry of the Main-Group ...
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17 votes

What's the pH of vinegar containg 5% acetic acid?

Consider the choices. Since it's acetic acid, you can rule out any pH values that indicate a basic or neutral solution. Knowing that acetic acid is a weak acid and that vinegar is a fairly dilute ...
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Why is the Haber process carried out at such high temperatures?

As others have pointed out, it is purely kinetics, but you may still wonder, why. For a reaction to actually occur (in both directions) and thus for an equilibrium to be reached, you need to overcome ...
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Can a zeroth order reaction be reversible?

A zeroth order reaction does not achieve equilibrium as a zeroth order reaction. Instead the kinetics will go away from zeroth order when we get close to the equilibrium condition. Zeroth order ...
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16 votes
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Which factors determine the keto:enol ratio for aldehydes, ketones, and 1,3-dicarbonyl compounds?

Your reasoning is along the right lines, but it is incomplete. enol of B is more stable because of more substituted alkene. The methyl group in acetone does stabilize the carbon-carbon double bond ...
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16 votes
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Formation of a stable hydrate

What can I say about (A) and (D)? When a carbonyl compound and water are present together, an equilibrium is set up between the carbonyl compound and the corresponding gem-diol. Like any equilibrium, ...
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16 votes
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What is the correct unit for the equilibrium constant?

Andselisk correctly identified the law of dilution and the name Ostwald is often connected with it. $$K_\text{dissociation} = \frac{\alpha^2}{1-\alpha}\cdot c$$ However, the degree of dissociation is $...
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What is the difference between chemical equilibrium and dynamic equilibrium?

Chemical equilibrium is a type of dynamic equilibrium, but not every dynamic equilibrium is a chemical equilibrium. In a chemical equilibrium there is no change on the macroscopic scale. That means ...
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What do curly brackets {} mean?

The curly brackets denote "activity of" the species therein. See the Wikipedia section: Basic definitions and properties of Equilibrium constant
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15 votes

What is active mass?

The term "active mass" is a historical term. The concept of an equilibrium constant was developed by Cato Maximilian Guldberg and Peter Waage. The Law of Mass Action has also been referred to as the ...
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15 votes
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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 ...
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15 votes

What is the difference between chemical equilibrium and dynamic equilibrium?

A chemical equilibrium concerns chemical reactions. There should be at least a forward- and backward reaction between two species but more complex systems with multiple individual reactions may occur. ...
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15 votes

Apparent paradox in the formation of ice at room temperature

Now that you've got $K_{eq}$, you need to take a look at the expression for the equilibrium constant, which is $$K_{eq} = \frac{a_{\text{ice}}}{a_{\text{water}}},$$ where $a$ is the activity of each ...
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Can the equilbrium constant ever be exactly 1?

For a chemical reaction, $$\Delta G = -R T \ln K_{eq}$$ $$\implies K_{eq} = e^{\frac{-\Delta G}{RT}} $$ Thus, in order for a chemical reaction to have $K_{eq}=1$*, it is necessary to have $\Delta G = ...
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14 votes
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Derivation of van 't Hoff equation for temperature dependence of equilibrium constant

The equation linking $\Delta H^\circ$ and $K$ is called the van 't Hoff equation. Since Philipp's comment on your question already links to a very thorough discussion of where the equation $\Delta G^\...
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14 votes
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Why exactly does precipitation occur?

Short story Maybe it will help to think first about a ridiculous case. Say you have a large hydrophilic solid, and a small drop of water is added on top. We would not expect the entire solid to ...
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