Practice Chemical Equilibrium in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

A dynamic state in a reversible reaction where the forward and reverse reactions proceed at equal rates, so the macroscopic concentrations of reactants and products.

The reaction is still happening both ways, but the amounts stay constant.

Showing a random 20 of 76 problems.

Example 1

easy
Does adding a catalyst shift the equilibrium position?

Example 2

easy
For H2(g)+I2(g)⇌2HI(g)\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g), at equilibrium [H2]=0.10 M[\text{H}_2] = 0.10\,\text{M}, [I2]=0.10 M[\text{I}_2] = 0.10\,\text{M}, and [HI]=0.80 M[\text{HI}] = 0.80\,\text{M}. Compute KcK_c.

Example 3

medium
For the reaction N2+3H2⇌2NH3\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3, at equilibrium [N2]=0.50 M[\text{N}_2] = 0.50\,\text{M}, [H2]=1.50 M[\text{H}_2] = 1.50\,\text{M}, and [NH3]=0.60 M[\text{NH}_3] = 0.60\,\text{M}. Calculate KeqK_{eq}.

Example 4

hard
For an endothermic reaction at equilibrium, predict the effect on KK of (a) raising TT, (b) adding an inert gas at constant volume.

Example 5

easy
At chemical equilibrium, what is true about the forward and reverse reaction rates?

Example 6

medium
For PCl5(g)⇌PCl3(g)+Cl2(g)\text{PCl}_5(g) \rightleftharpoons \text{PCl}_3(g) + \text{Cl}_2(g), Kc=0.040K_c = 0.040 at TT. If [PCl5]=0.10 M[\text{PCl}_5]=0.10\,\text{M}, [PCl3]=0.20 M[\text{PCl}_3]=0.20\,\text{M}, [Cl2]=0.10 M[\text{Cl}_2]=0.10\,\text{M}, compute QQ and predict the shift direction.

Example 7

challenge
For H2+I2⇌2HI\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI}, K=50K = 50. If [H2]0=[I2]0=1.00 M[\text{H}_2]_0 = [\text{I}_2]_0 = 1.00\,\text{M}, no HI initially, find [HI][\text{HI}] at equilibrium.

Example 8

medium
For 2SO2+O2⇌2SO32\text{SO}_2+\text{O}_2\rightleftharpoons2\text{SO}_3, at equilibrium [SO2]=0.20[\text{SO}_2]=0.20, [O2]=0.50[\text{O}_2]=0.50, [SO3]=0.40 M[\text{SO}_3]=0.40\,\text{M}. Find KK.

Example 9

medium
For A⇌B\text{A}\rightleftharpoons\text{B} with K=0.01K=0.01, are reactants or products favored, and by roughly how much?

Example 10

hard
Reaction 1: A⇌B\text{A} \rightleftharpoons \text{B} has K1=2K_1 = 2. Reaction 2: B⇌C\text{B} \rightleftharpoons \text{C} has K2=3K_2 = 3. Find KK for A⇌C\text{A} \rightleftharpoons \text{C}.

Example 11

medium
For N2O4⇌2NO2\text{N}_2\text{O}_4 \rightleftharpoons 2\text{NO}_2, K=0.211K = 0.211 at equilibrium [N2O4]=0.500 M[\text{N}_2\text{O}_4] = 0.500\,\text{M}. Find [NO2][\text{NO}_2].

Example 12

medium
At equilibrium in a reversible reaction, have the reactions stopped? Explain what is equal at equilibrium.

Example 13

challenge
Reaction X⇌Y\text{X}\rightleftharpoons\text{Y} has K=9K=9 at 300 K300\,\text{K} and K=4K=4 at 400 K400\,\text{K}. Is the forward reaction exothermic or endothermic? Explain.

Example 14

easy
If K≫1K\gg1 for a reaction at equilibrium, are products or reactants favored?

Example 15

easy
Which direction does CO(g)+H2O(g)⇌CO2(g)+H2(g)\text{CO}(g) + \text{H}_2\text{O}(g) \rightleftharpoons \text{CO}_2(g) + \text{H}_2(g) shift if H2\text{H}_2 is removed?

Example 16

hard
Reaction X⇌Y\text{X} \rightleftharpoons \text{Y} has K=16K = 16 at 25∘C25^\circ\text{C} and K=4K = 4 at 80∘C80^\circ\text{C}. Is the forward reaction exothermic or endothermic?

Example 17

hard
KcK_c for N2+3H2⇌2NH3\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3 is 0.500.50 at TT. Compute KcK_c for 12N2+32H2⇌NH3\tfrac{1}{2}\text{N}_2 + \tfrac{3}{2}\text{H}_2 \rightleftharpoons \text{NH}_3.

Example 18

medium
Acetic acid dissociates as HC2H3O2⇌H++C2H3O2−\text{HC}_2\text{H}_3\text{O}_2 \rightleftharpoons \text{H}^+ + \text{C}_2\text{H}_3\text{O}_2^- with Ka=1.8×10−5K_a = 1.8 \times 10^{-5}. Find [H+][\text{H}^+] in a 0.10 M0.10\,\text{M} solution.

Example 19

hard
KpK_p for N2+3H2⇌2NH3\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3 at T=500 KT = 500\,\text{K} is 1.5×10−5 atm−21.5 \times 10^{-5}\,\text{atm}^{-2}. Convert to KcK_c. Use R=0.0821 L atm/(mol K)R = 0.0821\,\text{L atm/(mol K)}.

Example 20

hard
If Kc=4.0K_c = 4.0 for A+B⇌C+D\text{A} + \text{B} \rightleftharpoons \text{C} + \text{D}, what is KcK_c for the reverse reaction C+D⇌A+B\text{C} + \text{D} \rightleftharpoons \text{A} + \text{B}?
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