AP Chemistry Flashcards: Reaction Quotient And Equilibrium Constant

What this deck covers

This deck focuses on Reaction Quotient And Equilibrium Constant, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: For $CaCO_3(s)\rightleftharpoons CaO(s)+CO_2(g)$, what is the correct $K_p$ expression?

Answer: $K_p=P_{CO_2}$. Solids omitted; only gas pressure appears.

Flashcard 2: What is $\Delta n_{gas}$ in $K_p=K_c(RT)^{\Delta n_{gas}}$ for $aA(g)\rightleftharpoons bB(g)$?

Answer: $\Delta n_{gas}=b-a$. Moles of gas products minus moles of gas reactants.

Flashcard 3: What happens to $K$ if the balanced equation is reversed?

Answer: $K_{rev}=\frac{1}{K}$. Reversing flips the fraction.

Flashcard 4: What happens to $K$ if all coefficients in the balanced equation are multiplied by $n$?

Answer: $K_{new}=K^n$. Each concentration term gets raised to the new coefficient.

Flashcard 5: For $2NO_2(g)\rightleftharpoons N_2O_4(g)$, what is the correct $Q_p$ expression?

Answer: $Q_p=\frac{P_{N_2O_4}}{(P_{NO_2})^2}$. Products over reactants with stoichiometric exponents.

Flashcard 6: If $K_c=2.0\times10^{4}$, which side is favored at equilibrium: reactants or products?

Answer: Products are favored. $K>>1$ means equilibrium lies far to the right.

Flashcard 7: If $K_c=5.0\times10^{-3}$, which side is favored at equilibrium: reactants or products?

Answer: Reactants are favored. $K<<1$ means equilibrium lies far to the left.

Flashcard 8: For $H_2(g)+I_2(g)\rightleftharpoons 2HI(g)$, what is $\Delta n_{gas}$?

Answer: $\Delta n_{gas}=0$. 2 moles gas products minus 2 moles gas reactants.

Flashcard 9: For $H_2(g)+I_2(g)\rightleftharpoons 2HI(g)$, what is the relationship between $K_p$ and $K_c$?

Answer: $K_p=K_c$. When $\Delta n_{gas}=0$, $(RT)^0=1$.

Flashcard 10: Calculate $Q_c$ for $A\rightleftharpoons B$ if $[A]=0.50$ and $[B]=2.0$.

Answer: $Q_c=4.0$. $Q_c=\frac{[B]}{[A]}=\frac{2.0}{0.50}=4.0$

Flashcard 11: Identify the shift for $A\rightleftharpoons B$ if $K_c=10$ and $Q_c=4$.

Answer: Shifts right (toward products). $Q<K$ means more products needed for equilibrium.

Flashcard 12: What is the expression for $Q_c$ for $aA+bB\rightleftharpoons cC+dD$ using concentrations?

Answer: $Q_c=\frac{[C]^c[D]^d}{[A]^a[B]^b}$. Products over reactants, each raised to its coefficient.

Flashcard 13: What is the expression for $Q_p$ for $aA(g)+bB(g)\rightleftharpoons cC(g)+dD(g)$ using partial pressures?

Answer: $Q_p=\frac{(P_C)^c(P_D)^d}{(P_A)^a(P_B)^b}$. Uses partial pressures instead of concentrations.

Flashcard 14: What is the definition of $K$ in terms of $Q$ for a reaction at equilibrium?

Answer: $K=Q$ at equilibrium. At equilibrium, reaction quotient equals equilibrium constant.

Flashcard 15: Which species are omitted from $Q$ and $K$: pure solids, pure liquids, solutes, or gases?

Answer: Pure solids and pure liquids are omitted. Their activities equal 1, so they don't affect the ratio.

Flashcard 16: What is the exponent on each term in $Q$ or $K$ relative to the balanced chemical equation?

Answer: Each exponent equals its stoichiometric coefficient. Reflects how many moles participate in the reaction.

Flashcard 17: Identify the correct comparison rule: if $Q<K$, which direction does the reaction shift to reach equilibrium?

Answer: Shifts right (toward products). System needs more products to reach equilibrium.

Flashcard 18: Identify the correct comparison rule: if $Q>K$, which direction does the reaction shift to reach equilibrium?

Answer: Shifts left (toward reactants). System has too many products relative to equilibrium.

Flashcard 19: Identify the correct comparison rule: if $Q=K$, what is the system’s status?

Answer: At equilibrium (no net shift). Forward and reverse rates are equal.

Flashcard 20: State the formula relating $K_p$ and $K_c$ using $\Delta n_{gas}$ and $R$ and $T$.

Answer: $K_p=K_c(RT)^{\Delta n_{gas}}$. Converts between pressure and concentration units.

Flashcard 21: State the formula for $Q_p$ for $aA(g)+bB(g) \rightleftharpoons cC(g)+dD(g)$ using partial pressures.

Answer: $Q_p = \frac{(P_C)^c(P_D)^d}{(P_A)^a(P_B)^b}$. Uses partial pressures instead of concentrations for gas-phase species.

Flashcard 22: What is the relationship between $K$ and $Q$ at equilibrium for a reaction mixture?

Answer: At equilibrium, $Q = K$. System reaches equilibrium when reaction quotient equals equilibrium constant.

Flashcard 23: State the formula for $Q_c$ for $aA + bB \rightleftharpoons cC + dD$ using molar concentrations.

Answer: $Q_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Products over reactants, each raised to its stoichiometric coefficient.

Flashcard 24: Which species are omitted from $Q$ and $K$ expressions: pure solids and pure liquids or aqueous solutes?

Answer: Pure solids and pure liquids are omitted. Their activities equal 1, so they don't affect the equilibrium expression.

Flashcard 25: What is the exponent on each term in a $Q$ or $K$ expression relative to the balanced chemical equation?

Answer: Each exponent equals its stoichiometric coefficient. Reflects how many moles of each species participate in the reaction.

Flashcard 26: Identify the correct reaction direction if $Q < K$ for the current mixture.

Answer: The reaction proceeds forward (toward products). More products must form to increase $Q$ until it equals $K$.

Flashcard 27: Identify the correct reaction direction if $Q > K$ for the current mixture.

Answer: The reaction proceeds in reverse (toward reactants). More reactants must form to decrease $Q$ until it equals $K$.

Flashcard 28: What is the correct conclusion if $Q = K$ for a reaction mixture at a fixed temperature?

Answer: The system is at equilibrium. No net change occurs; forward and reverse rates are equal.

Flashcard 29: State the expression for $K$ of the reverse reaction in terms of $K$ for the forward reaction.

Answer: $K_{\text{reverse}} = \frac{1}{K_{\text{forward}}}$. Products and reactants swap positions, inverting the ratio.

Flashcard 30: State the expression for $K$ when the entire balanced equation is multiplied by a factor $n$.

Answer: $K_{\text{new}} = K^n$. Each concentration term gets raised to the power $n$.