Question 1

What does an equilibrium state mean in a chemical reaction?

Accepted Answer

At equilibrium, the forward and reverse reaction rates are equal. The concentrations therefore remain constant, although the forward and reverse reactions continue and reactant or product amounts need not be equal.

Question 2

How is Kc calculated?

Accepted Answer

For aA + bB ⇌ cC + dD, Kc equals [C]^c[D]^d divided by [A]^a[B]^b. Every concentration in the expression is its equilibrium molar concentration, not the initial amount entered into an ICE table.

Question 3

How are Kp and Kc related?

Accepted Answer

The relation is Kp = Kc(RT) raised to the power Δng. The gas change Δng is calculated from the gaseous stoichiometric coefficients of products minus those of reactants in the balanced reaction as written.

Question 4

Why do pure solids not appear in a heterogeneous equilibrium expression?

Accepted Answer

A pure solid has unit activity under the standard convention. Therefore, for CaCO3(s) ⇌ CaO(s) + CO2(g), both solid activities are 1 and the expression reduces to Kp = pCO2.

Question 5

What happens to K when a reaction is changed?

Accepted Answer

Reversing a reaction changes K to 1/K, multiplying every coefficient by n raises K to the power n, and adding reactions multiplies their equilibrium constants. These transformations must be applied to both the equation and its K value.

Equilibrium Numbers Lab — Kc, Kp, K Tricks & Gases

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