Equilibrium and Le Chatelier's principle

What is dynamic equilibrium in a reversible reaction?

The forward and reverse reactions occur at equal rates, so concentrations remain constant

Which condition is necessary for a reversible reaction to establish equilibrium?

The system must be closed

What does Le Chatelier's principle predict?

How an equilibrium system responds to a change in conditions

For a reaction aA + bB ⇌ cC + dD, which expression represents Kc?

[C]^c[D]^d/[A]^a[B]^b

At a fixed temperature, what does a very large equilibrium constant usually indicate?

Products are strongly favored at equilibrium

Which change alters the value of an equilibrium constant for a particular reaction?

Changing the temperature

For A(g) + B(g) ⇌ C(g), what happens when more A is added at constant temperature and volume?

The equilibrium shifts right to consume some added A

For N2(g) + 3H2(g) ⇌ 2NH3(g), how does increasing pressure by decreasing volume affect the equilibrium position?

It shifts toward NH3 because that side has fewer moles of gas

When does a change in pressure generally have no effect on the position of a gaseous equilibrium?

When both sides contain the same total number of moles of gas

For an exothermic forward reaction, how does increasing temperature affect the equilibrium?

It shifts toward reactants and decreases the forward-reaction equilibrium constant

For an endothermic forward reaction, which change favors product formation at equilibrium?

Increasing the temperature

What is the effect of adding a catalyst to a system already at equilibrium?

It speeds up both directions equally and does not change the equilibrium position

If the reaction quotient Q is smaller than the equilibrium constant K, what occurs as equilibrium is approached?

The reaction proceeds in the forward direction to form more products

If Q is greater than K, which statement is correct?

The mixture contains too many products relative to equilibrium, so it shifts left

Why are pure solids and pure liquids omitted from equilibrium constant expressions?

Their effective concentrations are constant under the stated conditions

Consider CaCO3(s) ⇌ CaO(s) + CO2(g) in a closed container at constant temperature. What is the effect of adding more CaCO3(s) when both solids are already present?

The equilibrium position is unchanged because the amount of a pure solid is not in the equilibrium expression

At equilibrium, what can be said about reactant and product concentrations?

They remain constant over time but need not be equal

For 2SO2(g) + O2(g) ⇌ 2SO3(g), what is the expected effect of removing SO3 at constant temperature?

The equilibrium shifts right to replace some removed SO3