Chemistry: Chemical Equilibrium and Le Chatelier's Principle Worksheet

Question 1

For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), write the equilibrium constant expression, Kc.

Accepted Answer

The equilibrium expression is Kc = [NH3]^2 / ([N2][H2]^3). Pure solids and liquids are not included, but all species here are gases and are included.

Question 2

At equilibrium, the concentrations for H2(g) + I2(g) ⇌ 2HI(g) are [H2] = 0.20 M, [I2] = 0.20 M, and [HI] = 1.60 M. Calculate Kc.

Accepted Answer

Kc = [HI]^2 / ([H2][I2]) = (1.60)^2 / (0.20 × 0.20) = 2.56 / 0.040 = 64. The equilibrium constant is 64.

Question 3

For the equilibrium CO(g) + 2H2(g) ⇌ CH3OH(g), predict the shift if more CO is added to the container.

Accepted Answer

The equilibrium shifts to the right, toward products, because adding CO increases the reactant concentration. The system uses some of the added CO to form more CH3OH.

Question 4

For the equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g), predict the shift if SO3 is removed from the container.

Accepted Answer

The equilibrium shifts to the right, toward products, because removing SO3 lowers the product concentration. The system responds by producing more SO3.

Question 5

For the equilibrium N2O4(g) ⇌ 2NO2(g), the forward reaction is endothermic. Predict the shift when the temperature is increased.

Accepted Answer

The equilibrium shifts to the right, toward NO2, because heat acts like a reactant for an endothermic forward reaction. Increasing temperature favors the endothermic direction.

Question 6

For the equilibrium 2NO2(g) ⇌ N2O4(g), the forward reaction is exothermic. Predict the shift when the temperature is decreased.

Accepted Answer

The equilibrium shifts to the right, toward N2O4, because decreasing temperature favors the exothermic direction. The system produces heat to oppose the temperature decrease.

Question 7

For the equilibrium PCl5(g) ⇌ PCl3(g) + Cl2(g), predict the shift if the pressure is increased by decreasing the volume.

Accepted Answer

The equilibrium shifts to the left because the left side has 1 mole of gas and the right side has 2 moles of gas. Increasing pressure favors the side with fewer gas particles.

Question 8

For the equilibrium H2(g) + Cl2(g) ⇌ 2HCl(g), predict the shift if the volume is decreased.

Accepted Answer

There is no shift due to the volume change because both sides have 2 moles of gas. Changing volume does not favor either side when the number of gas particles is the same.

Question 9

For the equilibrium CaCO3(s) ⇌ CaO(s) + CO2(g), write the equilibrium constant expression, Kc.

Accepted Answer

The equilibrium expression is Kc = [CO2]. The solids CaCO3 and CaO are not included because pure solids do not appear in equilibrium expressions.

Question 10

For the reaction 2A(g) ⇌ B(g), Kc = 25 at a certain temperature. If [A] = 0.50 M and [B] = 2.0 M, calculate Qc and determine whether the reaction will shift left, shift right, or remain at equilibrium.

Accepted Answer

Qc = [B] / [A]^2 = 2.0 / (0.50)^2 = 2.0 / 0.25 = 8.0. Since Qc is less than Kc, the reaction shifts right to form more products.

Question 11

For the equilibrium Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq), the product FeSCN2+ is deep red. Predict the color change when more SCN- is added.

Accepted Answer

The solution becomes a deeper red because adding SCN- shifts the equilibrium to the right. More FeSCN2+ forms, increasing the red color.

Question 12

For the equilibrium 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g), predict the shift if pressure is increased by decreasing volume.

Accepted Answer

The equilibrium shifts to the left because the reactant side has 9 moles of gas and the product side has 10 moles of gas. Higher pressure favors the side with fewer gas particles.

Question 13

A catalyst is added to a reaction mixture already at equilibrium. Explain what happens to the position of equilibrium and to the rate at which equilibrium is reached.

Accepted Answer

The position of equilibrium does not change because a catalyst speeds up the forward and reverse reactions equally. A catalyst helps the system reach equilibrium faster, but it does not change K.

Question 14

For the equilibrium CO2(g) + H2(g) ⇌ CO(g) + H2O(g), Kc = 1.0 at a certain temperature. If the mixture contains [CO2] = 0.30 M, [H2] = 0.30 M, [CO] = 0.30 M, and [H2O] = 0.30 M, is the system at equilibrium?

Accepted Answer

Qc = ([CO][H2O]) / ([CO2][H2]) = (0.30 × 0.30) / (0.30 × 0.30) = 1.0. Since Qc equals Kc, the system is at equilibrium.

Question 15

For the equilibrium 2NO(g) + O2(g) ⇌ 2NO2(g), predict the shift when O2 is removed and explain how the concentration of NO changes.

Accepted Answer

The equilibrium shifts to the left because removing O2 lowers a reactant concentration. As the system shifts left, more NO is produced, so the concentration of NO increases.

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Chemistry: Chemical Equilibrium and Le Chatelier's Principle

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