Chapter 12 – Chemical Equilibrium

These flashcards cover essential concepts and equations regarding chemical equilibrium as discussed in Chapter 12.

What is chemical equilibrium?

The state when the concentrations of reactants and products remain constant over time (rate forward = rate reverse).

If there are more products than reactants at equilibrium, this means __________.

The reaction favors products.

If there are more reactants than products at equilibrium, this means __________.

The reaction favors reactants.

What is a dynamic equilibrium?

Equilibrium occurs when concentrations of [A], [B], [C], and [D] stop changing, while species do not stop forming or being destroyed.

In the reaction A + B ⇌ C + D, what do [C] and [D] represent?

The concentration of products.

In the reaction A + B ⇌ C + D, what do [A] and [B] represent?

The concentration of reactants.

What expression represents the equilibrium constant Kc?

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

What happens to the concentration of pure solids in an equilibrium constant?

Pure solids are omitted from Kc as their concentration is constant.

Are pure liquids included in the equilibrium constant Kc?

No, pure liquids are omitted for the same reason as solids.

At 25°C, the equilibrium constant for NH3(aq) + H2O(ℓ) ⇌ NH4+(aq) + OH-(aq) is what?

Kc = [NH4+][OH-] / [NH3].

What is the effect of temperature on Kc for endothermic reactions?

Kc increases as temperature increases.

What is the effect of temperature on Kc for exothermic reactions?

Kc decreases as temperature increases.

What illustrates Le Chatelier's principle?

If a system at equilibrium is disturbed, it will shift to minimize the disturbance.

What does it mean if the reaction is strongly product favored?

Very little reactant remains, often written as completion of reaction.

What does it mean if the reaction is strongly reactant favored?

Very little product forms, usually written as no reaction.

If Q < Kc, what must occur?

More product must be formed to reach equilibrium.

If Q > Kc, what must occur?

Less product must be formed to reach equilibrium.

What is the effect of increasing the volume of a gaseous reaction mixture?

The equilibrium will shift toward the side with more moles of gas.

In a reaction with no change in Δngas, how is K affected by a volume change?

Kc remains unchanged.

What is the formula to calculate Kp from Kc?

Kp = Kc(RT)^Δngas.

If Δngas is zero, how does a volume change affect the equilibrium?

No effect; concentrations remain unchanged.

How does adding an inert gas at constant volume affect the equilibrium?

It has no effect on the equilibrium concentrations.

What does a catalyst do to a reaction at equilibrium?

It speeds up both forward and reverse reactions but does not change equilibrium concentrations.

If the temperature is increased in an exothermic reaction, what happens to Kc?

Kc decreases.

For the reaction P + Q ⇌ R + S, what does the equilibrium constant Kc depend on?

On the concentrations of the products raised to their stoichiometric powers divided by the concentrations of the reactants raised to their stoichiometric powers.

What must happen to achieve equilibrium if Q < Kc?

The reaction will proceed forward.

What must happen to achieve equilibrium if Q > Kc?

The reaction will proceed in reverse.

What do you do to Kc if you multiply the entire reaction by a factor?

Raise Kc to the power of that factor.

If the reaction is reversed, what happens to Kc?

Kc becomes 1/Kc.

For the reaction N2 + 3H2 ⇌ 2NH3, what is Kc?

Kc = [NH3]^2 / [N2][H2]^3.

What does Kc indicate about the position of equilibrium?

It gives an indication of the relative amounts of products and reactants at equilibrium.

What characterizes a reaction at dynamic equilibrium?

Rates of forward and reverse reactions are equal.

What is included in Kp calculations?

Only gaseous components are included.

What can be said about pure solids at equilibrium?

Their concentrations don’t change over the course of the reaction.

At 25°C, what is the Kc for the reaction N2 + 3H2 ⇌ 2NH3 if it's known to be 5.6 x 10^5?

Kc for the reverse reaction is 1/(5.6 x 10^5).

What is a major factor influencing the direction of a shift in equilibrium according to Le Chatelier's Principle?

Changes in concentration, temperature, or pressure.

What happens to the equilibrium constant as ΔH changes?

Kc may increase or decrease depending on whether the reaction is endothermic or exothermic.

What does the term ‘reaction quotient’ Q represent?

The ratio of concentrations of products to reactants at any given point in time.

If a pure liquid is added to a reaction mixture at equilibrium, what is its effect?

It does not change the equilibrium constant.

How do you calculate Kc from known equilibrium concentrations?

Use the equilibrium expression Kc = [products]^coefficients / [reactants]^coefficients.

What is the effect of volume decrease on gaseous equilibria?

Shifts equilibrium toward the side with fewer moles of gas.

What does a change in pressure affect in a gaseous equilibrium?

It shifts equilibrium toward the side with fewer moles of gas.

When a reaction moves to the right, which side is favored?

The product side is favored.

If we double the volume of a gas at equilibrium, what happens?

The equilibrium position shifts toward the side with more moles of gaseous species.

What does the symbol Δngas represent?

The change in the number of moles of gas during the reaction.

In a reaction at equilibrium, what is true of the rates of reaction?

They are equal for both the forward and reverse reactions.

What do you determine from observed concentrations of reactants and products?

The reaction quotient Q, to predict the direction of the equilibrium shift.

What happens to reaction rates if a catalyst is added?

Both the forward and backward rates increase, but K remains unchanged.

What happens to Kp if Kc is known and you want to find Kp?

Use Kp = Kc(RT)^Δngas.

If Kc = 10, what will Kc be if the equation is reversed?

Kc will be 0.1 (1/Kc).

What happens to equilibrium if a product is removed?

The equilibrium shifts toward the right to produce more product.

What does [product]^m represent in terms of Kc?

The concentration of the product raised to the power of its stoichiometric coefficient.