Question

An important reaction in the commercial production of hydrogen is $$ \mathrm{CO}(\mathrm{g})+\mathrm{H}_{2} \mathrm{O}(g) \rightleftharpoons \mathrm{H}_{2}(\mathrm{~g})+\mathrm{CO}_{2}(g) $$ How will this system at equilibrium shift in each of the five following cases? a. Gaseous carbon dioxide is removed. b. Water vapor is added. c. In a rigid reaction container, the pressure is increased by adding helium gas. d. The temperature is increased (the reaction is exothermic). e. The pressure is increased by decreasing the volume of the reaction container.

Short answer

a. The system will shift to the right, favoring the formation of hydrogen and carbon dioxide. b. The system will shift to the right, favoring the formation of hydrogen and carbon dioxide. c. There will be no shift in the reaction equilibrium. d. The system will shift to the left, favoring the formation of carbon monoxide and water vapor. e. There will be no shift in the reaction equilibrium.

Step-by-step solution

Identify affected component and direction

Gaseous carbon dioxide (CO₂) is a product of the reaction. Since it is removed, its concentration will decrease.

Apply Le Chatelier's principle

To counteract the decrease in CO₂ concentration, the system will shift the equilibrium to the right (production of more CO₂). Thus, the reaction will favor the formation of hydrogen and carbon dioxide. #b. Water vapor is added.#

Identify affected component and direction

Water vapor (H₂O) is a reactant in the reaction. Since it is added, its concentration will increase.

Apply Le Chatelier's principle

To counteract the increase in H₂O concentration, the system will shift the equilibrium to the right. Thus, the reaction will favor the formation of hydrogen and carbon dioxide. #c. In a rigid reaction container, the pressure is increased by adding helium gas.#

Identify affected component and direction

The pressure is increased by adding helium gas (an inert gas). This change does not directly affect the concentrations of the reactants or products in the reaction.

Apply Le Chatelier's principle

Since there is no change in the concentrations of the components, the system's equilibrium position will not be affected. Therefore, there will be no shift in the reaction equilibrium. #d. The temperature is increased (the reaction is exothermic).#

Identify affected component and direction

The temperature of the system is increased. Since the reaction is exothermic, heat can be considered as a product.

Apply Le Chatelier's principle

To counteract the increase in temperature, the system will shift the equilibrium to the left (consume more heat). Thus, the reaction will favor the formation of carbon monoxide and water vapor. #e. The pressure is increased by decreasing the volume of the reaction container.#

Identify affected component and direction

The pressure is increased by decreasing the volume of the reaction container. This change will affect the concentrations of the reactants and products equally.

Determine the shift direction based on the number of moles of gas

Since the number of moles of gas on the left side (CO + H₂O) is equal to the number of moles on the right side (H₂ + CO₂), the reaction's equilibrium position will not shift in response to the pressure change. Thus, there will be no shift in the reaction equilibrium.

Key concepts

Equilibrium Shift

Le Chatelier's principle helps us predict how a chemical reaction at equilibrium responds to external changes. When a system is disturbed, it will try to restore balance by shifting its equilibrium position. Various factors such as the removal or addition of substances, pressure changes, and temperature variations can cause this shift.

• When a product, like carbon dioxide in our example reaction, is removed, the system shifts to produce more of that product. It moves in the direction that will counteract the disturbance.
• Likewise, adding more of a reactant, such as water vapor, compels the system to shift towards forming more products, thus restoring equilibrium.
• Importantly, inert gases like helium do not affect the system's equilibrium as they do not change reactant or product concentrations.

Understanding these dynamics allows us to predict the outcome of changes applied to a chemical reaction system.

Chemical Reaction

A chemical reaction involves the rearrangement of atoms to form new substances. In our reaction between carbon monoxide (CO) and water vapor (H₂O), these reactants transform into hydrogen gas (H₂) and carbon dioxide (CO₂).

• One critical aspect of reactions is the dynamic yet stable nature of equilibrium. At equilibrium, the forward and reverse reactions occur at equal rates, resulting in constant concentrations of reactants and products.
• Changes to the system, like adding or removing substances, disrupt this balance. Consequently, the reaction will adjust to restore equilibrium, either by making more products or reactants.
• In the case of adding more water vapor, there will be a shift towards producing more hydrogen and carbon dioxide to rebalance the system.

Grasping these processes is crucial for mastering how reactions function and under what conditions they are optimized.

Pressure Effects

Pressure can influence reaction equilibrium, especially for reactions involving gases. Le Chatelier's principle assists in predicting such effects. However, the response to pressure alterations depends on how these changes are made.

• For example, increasing the system's pressure by adding a non-reactive gas like helium does not change the concentration of the reactants or products, leaving the equilibrium unaltered. This is because only gas molecules involved in the reaction can shift equilibrium.
• Decreasing the container's volume, another method of increasing pressure, can also affect equilibrium. However, for reactions with equal numbers of moles on both sides, like our example, there is no shift. This is because the reaction system lacks a favored side that would counteract the change in pressure.

Understanding pressure effects is crucial in industrial applications where controlling reaction conditions is vital for efficiency.

Temperature Effects

Temperature changes play a crucial role in influencing chemical equilibrium. When temperature is altered, it affects the kinetic energy of molecules, potentially shifting the equilibrium position. For our reaction, which is exothermic, heat is released as a product.

• Increasing temperature adds more heat to the system. According to Le Chatelier's principle, the reaction will shift to consume this excess heat, moving towards the endothermic side (left side) of the equation.
• Thus, the reaction favors the formation of the reactants, carbon monoxide and water vapor, rather than producing additional hydrogen and carbon dioxide.
• This principle enables chemists to control reaction outcomes by adjusting temperature, either boosting reactant formation or product yield as necessary.

Mastering temperature's impact on equilibrium provides a pathway to optimizing reactions for various practical applications.