AP Chem unit 7 Le Chatelier principle practice questions

What is Le Chatelier's Principle?

A principle stating that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.

True or False: Le Chatelier's Principle applies only to gaseous reactions.

False. It applies to all types of equilibria, including solids, liquids, and gases.

Effect of increasing concentration of reactants?

Shifts equilibrium to products - favors the forward reaction.

Fill in the blank: Le Chatelier's Principle predicts the response of a system at ________.

equilibrium.

How does temperature affect equilibrium?

Increasing temperature shifts equilibrium in the direction of the endothermic reaction.

Question: What happens when pressure increases in a gaseous equilibrium?

Equilibrium shifts to the side with fewer moles of gas.

Compare endothermic and exothermic reactions in terms of temperature changes.

- Endothermic: Heat is a reactant; increasing temp shifts right. - Exothermic: Heat is a product; increasing temp shifts left.

Cause: Decrease in volume of a gas mixture. What is the effect?

Shifts equilibrium toward the side with fewer moles of gas.

What does it mean if a system is at equilibrium?

The rates of the forward and reverse reactions are equal, and concentrations remain constant.

True or False: Adding an inert gas at constant volume changes equilibrium position.

False. It does not affect concentrations of reactants/products.

Effect of removing a product from equilibrium?

Shifts equilibrium to the right - favors the production of more products.

What is the effect of adding heat to an exothermic reaction?

Shifts equilibrium to the left - favors the reactants.

What happens when a catalyst is added to an equilibrium system?

No shift in equilibrium position; it only speeds up the rates of both the forward and reverse reactions equally.

Describe the dynamic nature of equilibrium.

Equilibrium is dynamic; the forward and reverse reactions continue at equal rates.

Fill in the blank: Le Chatelier's Principle helps predict the ________ of equilibrium systems to changes.

response.

How does increasing temperature affect an exothermic reaction at equilibrium?

It shifts equilibrium to the left, favoring the reactants.

How does increasing temperature affect an exothermic reaction?

According to Le Chatelier's Principle, increasing temperature shifts equilibrium to the left, favoring reactants.

True or False: Decreasing pressure shifts equilibrium towards the side with more gas molecules.

False. Decreasing pressure shifts equilibrium towards the side with fewer gas molecules.

Effect of adding a catalyst on equilibrium?

A catalyst speeds up the rate of both forward and reverse reactions equally; no change in equilibrium position.

Increasing concentration of reactants will lead to...

A shift to the right, favoring the formation of products.

What is the effect of decreasing temperature on an endothermic reaction?

It shifts equilibrium to the left, favoring reactants.

CaCl2(s) ⇌ Ca^2+(aq) + 2Cl^−(aq). Effect of adding CaCl2?

Adding CaCl2 shifts equilibrium to the right, producing more ions.

Fill in the blank: Increasing pressure shifts equilibrium to the side with ____ gas molecules.

Fewer.

Effect of removing a product on equilibrium?

Removing a product shifts equilibrium to the right, favoring product formation.

True or False: Changes in concentration affect the equilibrium constant.

False. Changes in concentration do not affect the equilibrium constant itself.

What happens to equilibrium when a system is compressed?

It shifts towards the side with fewer gas molecules to relieve stress.

Example: Effect of heating N2(g) + 3H2(g) ⇌ 2NH3(g).

Heating favors the reactants; equilibrium shifts left.

What effect does adding an inert gas have on equilibrium?

Adding an inert gas at constant volume does not affect the position of equilibrium.

Cause: Dilution of a solution. Effect?

Dilution decreases concentration of all species, shifting equilibrium towards the side with more moles.

CaO(s) + CO2(g) ⇌ CaCO3(s). Effect of increasing CO2?

Increasing CO2 shifts equilibrium to the right, producing more CaCO3.

What is the general effect of decreasing volume on gas equilibria?

Decreasing volume increases pressure, shifting equilibrium towards fewer gas molecules.

Example of Le Chatelier's principle in action?

Carbonated beverages: opening a bottle causes CO2 to escape, shifting equilibrium to produce more CO2.

What happens to equilibrium when concentration is increased?

The system shifts to the right, favoring products, to reduce the increased concentration.

True or False: Adding a catalyst affects equilibrium position.

False – A catalyst speeds up both forward and reverse reactions equally, not affecting equilibrium position.

Effect of increasing temperature on an exothermic reaction?

The equilibrium shifts left, favoring reactants as heat is treated as a product.

Cause → Effect: Increase in pressure on gaseous equilibrium.

Shift towards the side with fewer moles of gas, reducing pressure.

What is the equilibrium expression for: 2A + B ⇌ C?

The expression is: $\displaystyle K_c = \\frac{[C]}{[A]^2[B]}$.

Increase in volume effect on equilibrium?

The equilibrium shifts towards the side with more moles of gas to counteract volume increase.

Effect of decreasing concentration of reactants?

The equilibrium shifts left, favoring reactants to counteract the decrease.

True or False: Removing a product shifts equilibrium right.

True – Removing a product shifts equilibrium towards the right to produce more products.

Comparison: Change in temperature vs. change in pressure effects.

Temperature changes affect all equilibria; pressure changes primarily affect gaseous reactions.

Fill in the blank: An increase in pressure favors the side with _____ moles of gas.

fewer – This helps to decrease pressure.

Effect of decreasing temperature on an endothermic reaction?

The equilibrium shifts left, favoring reactants as heat is treated as a reactant.

What happens when a system at equilibrium is disturbed?

According to Le Chatelier's Principle, the system shifts to counteract the disturbance.

Example: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Effect of increased N₂?

The equilibrium shifts right, favoring NH₃ production.

True or False: Pressure changes affect solid equilibria.

False – Solids have constant volume; pressure changes do not affect them.

What is the impact of decreasing volume on a reaction with more gas moles?

The equilibrium shifts toward the side with fewer gas moles to reduce pressure.

Increasing concentration of products effect?

The equilibrium shifts left, favoring reactants to reduce product concentration.