18.2 Shifting Equilibrium

Summary

This video delves into Le Chatelier's Principle, explaining how changes in pressure, concentration, and temperature shift the equilibrium of chemical systems. Using the Haber process as an example, it shows how pressure affects reactions involving gases, particularly ammonia synthesis. It explores how altering the concentration of reactants or products shifts equilibrium and discusses the influence of temperature on reaction rates and equilibrium constants. The video also explains irreversible reactions, the common ion effect, and the three main ways reactions go to completion: gas formation, precipitation, and slightly ionized products, making the concepts accessible and engaging.

Takeaways

• 😀 Le Chatelier's Principle states that when a system at equilibrium is stressed, it shifts to relieve that stress.
• 😀 Pressure affects chemical reactions involving gases, shifting the equilibrium towards the side with fewer gas molecules to reduce pressure.
• 😀 In the Haber process, increasing pressure favors ammonia production by shifting the equilibrium to the right.
• 😀 Changes in concentration can shift equilibrium, but they do not affect the equilibrium constant (K).
• 😀 Adding more of a reactant shifts the equilibrium to the right, while removing reactants shifts it to the left.
• 😀 Increasing the concentration of a product shifts the equilibrium to the left, while decreasing it shifts it to the right.
• 😀 Pure solids and liquids do not affect the equilibrium position because their concentrations are constant.
• 😀 Changes in temperature affect the equilibrium constant (K), shifting the equilibrium position depending on whether the reaction is exothermic or endothermic.
• 😀 In an exothermic reaction, increasing temperature shifts equilibrium to the left, while decreasing temperature shifts it to the right.
• 😀 Reactions can go to completion if they form a gas, a precipitate, or a slightly ionized product, preventing reverse reactions.
• 😀 The common ion effect describes how adding ions already present in a solution can shift the equilibrium, leading to precipitation or other changes in concentration.

Q & A

What does Le Chatelier's Principle state?

Le Chatelier's Principle states that when a system experiences a stress (such as a change in pressure, concentration, or temperature), it will shift its equilibrium in the direction that relieves this stress. This can either be physical or chemical in nature.

How does pressure affect the equilibrium of a chemical reaction?

Pressure only affects chemical reactions involving gases. When pressure is increased, the system will shift in a direction that reduces the number of gas molecules, thus relieving the pressure. For example, in the Haber process, an increase in pressure shifts the equilibrium towards the production of more ammonia, as it reduces the number of gas molecules.

Why does a change in pressure only affect reactions involving gases?

A change in pressure only affects reactions involving gases because gases are more sensitive to volume changes. The number of gas molecules in a given volume can change, which allows the system to shift equilibrium to adjust to the new pressure.

What happens when the concentration of a reactant is increased in a chemical reaction?

When the concentration of a reactant is increased, the equilibrium shifts to the right to produce more products. This is to restore the ratio of reactants and products as determined by the equilibrium constant.

How does the addition of a product affect the equilibrium of a reaction?

Increasing the concentration of a product shifts the equilibrium to the left, favoring the formation of more reactants. Conversely, decreasing the concentration of a product shifts the equilibrium to the right to produce more products.

What is the role of solids and liquids in equilibrium expressions?

Pure solids and pure liquids do not change their concentrations in equilibrium and, therefore, do not appear in the equilibrium expression. Only the concentrations of gases and aqueous solutions are considered.

How does temperature affect the equilibrium constant?

Temperature changes affect the equilibrium constant (K). An increase in temperature can shift the equilibrium of a reaction, especially in endothermic or exothermic reactions, and will alter the value of K. This occurs because temperature influences the rate of the forward and reverse reactions differently.

What happens in an endothermic reaction when heat is added?

In an endothermic reaction, adding heat shifts the equilibrium towards the reactants, favoring the reverse reaction. This happens because the system tries to absorb the added heat, thus breaking bonds and producing more of the reactants.

What is the common ion effect and how does it influence equilibrium?

The common ion effect occurs when a substance is added to a solution that shares an ion with the reactants in a reversible reaction. This increases the concentration of that ion and shifts the equilibrium to the left, favoring the formation of more reactants and potentially causing precipitation of a solid.

What are the three main ways in which a reaction can go to completion?

A reaction can go to completion in three main ways: (1) by forming a gas that bubbles out of the solution, (2) by forming a precipitate that settles out, or (3) by forming a slightly ionized product that doesn't react back into the reactants.