Question

An important reaction in the commercial production of hydrogen is $$ \mathrm{CO}(g)+\mathrm{H}_{2} \mathrm{O}(g) \rightleftharpoons \mathrm{H}_{2}(g)+\mathrm{CO}_{2}(g) $$ 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, producing more H₂(g) and CO₂(g). b. The system will shift to the right, producing more H₂(g) and CO₂(g). c. The system remains at the same equilibrium point. d. The system will shift to the left, producing more CO(g) and H₂O(g). e. The system remains at the same equilibrium point.

Step-by-step solution

Case a: Gaseous carbon dioxide is removed.

When gaseous carbon dioxide is removed from the equilibrium system, according to Le Châtelier's principle, the system will shift to the side that produces gaseous carbon dioxide to counteract the disturbance and restore equilibrium. So, the system will shift to the right, producing more H₂(g) and CO₂(g).

Case b: Water vapor is added.

When water vapor is added to the equilibrium system, this disturbs the balance in favor of the reactants. According to Le Châtelier's principle, the system will shift to the side that reduces the amount of water vapor to restore equilibrium. Therefore, the system will shift to the right, producing more H₂(g) and CO₂(g).

Case c: Pressure is increased by adding helium gas.

Adding helium gas to a rigid reaction container increases the pressure, but it does not directly affect the number of moles of any component in the reaction. Hence, the change in pressure does not result in a shift in the equilibrium of the reaction. The system remains at the same equilibrium point.

Case d: Temperature is increased (the reaction is exothermic).

Since the reaction is exothermic, increasing the temperature adds heat to the equilibrium system. According to Le Châtelier's principle, the system will try to minimize the disturbance by shifting to the side that consumes the added heat. In this case, heat is produced in the forward reaction (CO + H₂O → H₂ + CO₂), so the system will shift to the left, producing more CO(g) and H₂O(g).

Case e: Pressure is increased by decreasing the volume of the reaction container.

Decreasing the volume of the reaction container increases the pressure in the system. According to Le Châtelier's principle, the system will shift to the side with fewer moles of gas to reduce the pressure and restore equilibrium. In this reaction, there are equal numbers of moles of reactants and products (1 mol of CO + 1 mol of H₂O ⇌ 1 mol of H₂ + 1 mol of CO₂), so the change in volume does not result in a shift in the equilibrium of the reaction, and the system remains at the same equilibrium point.

Key concepts

Chemical Equilibrium

Chemical equilibrium refers to a state in a reversible chemical reaction where the rates of the forward and reverse reactions are equal. At this point, the concentrations of the reactants and products remain constant over time. This does not necessarily mean that the concentrations of reactants and products are equal, but that their ratios remain constant. Chemical equilibrium is dynamic, meaning that reactions continue to occur, but without any net change.
The concept of equilibrium is central to understanding how reactions respond to various changes in conditions. This can be particularly important in industrial settings, where maximizing the yield of desired products is critical.
Factors that can affect equilibrium include changes in concentration, temperature, and pressure. Each of these can cause a reaction to shift, favoring either the forward or reverse reaction, according to Le Chatelier's Principle.

Reaction Shifts

Reaction shifts occur in response to changes in concentration, pressure, volume, or temperature. According to Le Chatelier's Principle, if a system at equilibrium is subjected to an external change, the system will adjust itself to minimize the effect of that change and restore a new equilibrium.
For example:

• If a reactant or product is added, the equilibrium will shift to consume the added substance.
• If a reactant or product is removed, the equilibrium will shift to produce more of the removed substance.
• Changing the pressure by altering the volume impacts reactions involving gases, encouraging shifts to the side with fewer or more moles of gas, depending on the change.

Understanding these shifts helps chemists predict how changes in the environment will affect the outcome of a reaction, allowing for improved control over reaction conditions.

Exothermic Reaction

An exothermic reaction is a chemical reaction that releases heat into its surroundings. In these reactions, the energy of the products is lower than that of the reactants. As such, heat can be considered a product of the reaction.
When temperature changes occur in an exothermic reaction, Le Chatelier's Principle helps predict how the equilibrium will shift. Increasing the temperature results in more heat in the system, prompting the system to shift towards the endothermic direction to absorb the extra heat, which is the reverse direction for exothermic reactions.
Conversely, decreasing the temperature will cause the system to favor the exothermic direction, producing more heat to compensate for the temperature drop. This concept is crucial in industrial chemistry where temperature control is used to maximize yields or manage reaction speed.

Gas Laws in Chemistry

Gas laws in chemistry describe the behavior of gases and how they respond to changes in conditions such as pressure, volume, and temperature. These principles are essential for understanding reactions involving gases, particularly those in equilibrium states.

• Boyle's Law: States that for a given mass of gas at constant temperature, the product of pressure and volume is constant. (P₁V₁ = P₂V₂)
• Charles's Law: States that the volume of a given mass of gas is directly proportional to its temperature at constant pressure. (V₁/T₁ = V₂/T₂)
• Avogadro's Law: States that equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules.

These laws are critical for predicting how changes will impact the behavior of gases in a reaction, aiding in the understanding of reaction dynamics and equilibrium.