AP Chemistry Flashcards: Calculating Equilibrium Concentrations

What this deck covers

This deck focuses on Calculating Equilibrium Concentrations, 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 the reaction $CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(g)$, write the $K_c$ expression.

Answer: $K_c = \frac{[CO_2][H_2O]^2}{[CH_4][O_2]^2}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 2: Calculate $K_c$ for $H_2 + I_2 \rightleftharpoons 2HI$ with $[H_2] = 1M$, $[I_2] = 1M$, $[HI] = 2M$.

Answer: $K_c = \frac{4}{1}$. $K_c = \frac{[HI]^2}{[H_2][I_2]} = \frac{2^2}{1 \times 1} = 4$.

Flashcard 3: State the effect of adding a reactant on the equilibrium position.

Answer: Shifts right to form more products. Le Chatelier's principle: system responds by consuming the added reactant.

Flashcard 4: What is the effect of a catalyst on the equilibrium constant $K$?

Answer: No effect. Catalysts only affect reaction rate, not equilibrium position or $K$.

Flashcard 5: Identify the equilibrium expression for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.

Answer: $K_c = \frac{[NH_3]^2}{[N_2][H_2]^3}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 6: State the relationship between $K_p$ and $K_c$ for gaseous reactions.

Answer: $K_p = K_c(RT)^{\Delta n}$. Where $\Delta n$ is moles of gaseous products minus gaseous reactants.

Flashcard 7: State the unit for $K_c$ for the reaction $aA + bB \rightleftharpoons cC + dD$ if $c+d = a+b$.

Answer: Unitless. When total moles of products equals total moles of reactants.

Flashcard 8: What happens to $K_c$ of an exothermic reaction when temperature increases?

Answer: $K_c$ decreases. Higher temperature opposes exothermic reactions, decreasing $K_c$.

Flashcard 9: Find $K_c$ for the reaction $2A \rightleftharpoons B + C$ if $[A] = 0.5M$, $[B] = 1M$, $[C] = 1M$.

Answer: $K_c = \frac{1 \times 1}{0.5^2}$. $K_c = \frac{[B][C]}{[A]^2} = \frac{1 \times 1}{0.5^2} = 4$.

Flashcard 10: For the reaction $2NO(g) + O_2(g) \rightleftharpoons 2NO_2(g)$, what is the $K_p$ expression?

Answer: $K_p = \frac{P_{NO_2}^2}{P_{NO}^2 P_{O_2}}$. Products over reactants using partial pressures, raised to coefficients.

Flashcard 11: What is the effect of adding an inert gas at constant volume on the equilibrium of a reaction?

Answer: No effect. Inert gas doesn't participate and doesn't change partial pressures.

Flashcard 12: For the endothermic reaction $A \rightleftharpoons B$, what is the effect of increasing temperature?

Answer: Shifts towards $B$. Higher temperature favors endothermic reactions (heat-absorbing direction).

Flashcard 13: For the reaction $C(s) + CO_2(g) \rightleftharpoons 2CO(g)$, write the $K_c$ expression.

Answer: $K_c = [CO]^2/[CO_2]$. Solid carbon is excluded, only gaseous species are included.

Flashcard 14: Given $K_c = 10$ for $A \rightleftharpoons B$, find $K_c$ for $2A \rightleftharpoons 2B$.

Answer: $K_c = 10^2$. When reaction is doubled, equilibrium constant is squared.

Flashcard 15: What happens to the equilibrium position when pressure is increased for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

Answer: Shifts towards $NH_3$. Higher pressure favors the side with fewer gas molecules (2 vs 4).

Flashcard 16: What happens to the equilibrium position when pressure is increased for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

Answer: Shifts towards $NH_3$. Higher pressure favors the side with fewer gas molecules (2 vs 4).

Flashcard 17: Identify the equilibrium expression for $CO(g) + Cl_2(g) \rightleftharpoons COCl_2(g)$.

Answer: $K_c = \frac{[COCl_2]}{[CO][Cl_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 18: What is the equilibrium constant expression for $2H_2O_2(aq) \rightleftharpoons 2H_2O(l) + O_2(g)$?

Answer: $K_c = [O_2]$. Liquids are excluded from equilibrium expressions, only gases included.

Flashcard 19: State the $K_c$ expression for the reaction $C_2H_4(g) + H_2(g) \rightleftharpoons C_2H_6(g)$.

Answer: $K_c = \frac{[C_2H_6]}{[C_2H_4][H_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 20: What is the equilibrium expression for $H_2(g) + S(s) \rightleftharpoons H_2S(g)$?

Answer: $K_c = [H_2S]$. Solids are excluded from equilibrium expressions, only gases included.

Flashcard 21: State the unit for $K_c$ for the reaction $aA + bB \rightleftharpoons cC + dD$ if $c+d = a+b$.

Answer: Unitless. When total moles of products equals total moles of reactants.

Flashcard 22: For $2NO_2(g) \rightleftharpoons N_2O_4(g)$, what happens to $K_c$ if temperature is increased?

Answer: $K_c$ decreases. Higher temperature opposes exothermic reactions, decreasing $K_c$.

Flashcard 23: For the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, find $K_c$ if $[HI] = 2M$, $[H_2] = 1M$, $[I_2] = 1M$.

Answer: $K_c = 4$. $K_c = \frac{[HI]^2}{[H_2][I_2]} = \frac{2^2}{1 \times 1} = 4$.

Flashcard 24: For the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, find $K_c$ if $[HI] = 2M$, $[H_2] = 1M$, $[I_2] = 1M$.

Answer: $K_c = 4$. $K_c = \frac{[HI]^2}{[H_2][I_2]} = \frac{2^2}{1 \times 1} = 4$.

Flashcard 25: What is the effect of a catalyst on the equilibrium constant $K$?

Answer: No effect. Catalysts only affect reaction rate, not equilibrium position or $K$.

Flashcard 26: What is the equilibrium expression for $H_2(g) + S(s) \rightleftharpoons H_2S(g)$?

Answer: $K_c = [H_2S]$. Solids are excluded from equilibrium expressions, only gases included.

Flashcard 27: For the reaction $CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(g)$, write the $K_c$ expression.

Answer: $K_c = \frac{[CO_2][H_2O]^2}{[CH_4][O_2]^2}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 28: If $K_c = 1.5$ for the reaction $A \rightleftharpoons B$, what is the value of $K_c$ for $B \rightleftharpoons A$?

Answer: $K_c = \frac{1}{1.5}$. For the reverse reaction, $K_c$ becomes the reciprocal of the original.

Flashcard 29: If $K_c = 1.5$ for the reaction $A \rightleftharpoons B$, what is the value of $K_c$ for $B \rightleftharpoons A$?

Answer: $K_c = \frac{1}{1.5}$. For the reverse reaction, $K_c$ becomes the reciprocal of the original.

Flashcard 30: State the relationship between $K_p$ and $K_c$ for gaseous reactions.

Answer: $K_p = K_c(RT)^{\Delta n}$. Where $\Delta n$ is moles of gaseous products minus gaseous reactants.

Flashcard 31: What is the effect of adding an inert gas at constant volume on the equilibrium of a reaction?

Answer: No effect. Inert gas doesn't participate and doesn't change partial pressures.

Flashcard 32: What is the expression for the equilibrium constant $K_c$ for the reaction $aA + bB \rightleftharpoons cC + dD$?

Answer: $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$. Products in numerator raised to their coefficients, reactants in denominator.

Flashcard 33: For the reaction $PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)$, what is the effect of decreasing temperature?

Answer: Shifts towards $PCl_5$. Lower temperature favors the exothermic direction (heat-producing side).

Flashcard 34: For the reaction $2NO(g) + O_2(g) \rightleftharpoons 2NO_2(g)$, what is the $K_p$ expression?

Answer: $K_p = \frac{P_{NO_2}^2}{P_{NO}^2 P_{O_2}}$. Products over reactants using partial pressures, raised to coefficients.

Flashcard 35: For the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, find $K_c$ if $[HI] = 2M$, $[H_2] = 1M$, $[I_2] = 1M$.

Answer: $K_c = 4$. $K_c = \frac{[HI]^2}{[H_2][I_2]} = \frac{2^2}{1 \times 1} = 4$.

Flashcard 36: What is the effect of adding a product on the position of equilibrium?

Answer: Shifts left to form more reactants. Le Chatelier's principle: system responds by consuming the added product.

Flashcard 37: Calculate $K_c$ for $H_2 + I_2 \rightleftharpoons 2HI$ with $[H_2] = 1M$, $[I_2] = 1M$, $[HI] = 2M$.

Answer: $K_c = \frac{4}{1}$. $K_c = \frac{[HI]^2}{[H_2][I_2]} = \frac{2^2}{1 \times 1} = 4$.

Flashcard 38: State the $K_c$ expression for the reaction $C_2H_4(g) + H_2(g) \rightleftharpoons C_2H_6(g)$.

Answer: $K_c = \frac{[C_2H_6]}{[C_2H_4][H_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 39: Identify the equilibrium expression for $CO(g) + Cl_2(g) \rightleftharpoons COCl_2(g)$.

Answer: $K_c = \frac{[COCl_2]}{[CO][Cl_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 40: For $A \rightleftharpoons B + C$, if $K_c = 2$, what is $K_c$ for $B + C \rightleftharpoons A$?

Answer: $K_c = \frac{1}{2}$. For the reverse reaction, $K_c$ becomes the reciprocal of the original.

Flashcard 41: Find $K_c$ for $A \rightleftharpoons 2B$ if $[A] = 1M$, $[B] = 0.5M$ at equilibrium.

Answer: $K_c = \frac{0.5^2}{1}$. $K_c = \frac{[B]^2}{[A]} = \frac{0.5^2}{1} = 0.25$.

Flashcard 42: Given $K_c = 10$ for $A \rightleftharpoons B$, find $K_c$ for $2A \rightleftharpoons 2B$.

Answer: $K_c = 10^2$. When reaction is doubled, equilibrium constant is squared.

Flashcard 43: What is the effect of pressure decrease on equilibrium of $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

Answer: Shifts left. Lower pressure favors the side with more gas molecules (4 vs 2).

Flashcard 44: State the unit for $K_c$ for the reaction $aA + bB \rightleftharpoons cC + dD$ if $c+d = a+b$.

Answer: Unitless. When total moles of products equals total moles of reactants.

Flashcard 45: For the reaction $CH_4(g) + 2O_2(g) \rightleftharpoons CO_2(g) + 2H_2O(g)$, write the $K_c$ expression.

Answer: $K_c = \frac{[CO_2][H_2O]^2}{[CH_4][O_2]^2}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 46: For the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, what is the expression for $K_p$?

Answer: $K_p = \frac{P_{SO_3}^2}{P_{SO_2}^2 P_{O_2}}$. Products over reactants using partial pressures, raised to coefficients.

Flashcard 47: State the effect of adding a reactant on the equilibrium position.

Answer: Shifts right to form more products. Le Chatelier's principle: system responds by consuming the added reactant.

Flashcard 48: Identify the equilibrium expression for $CO(g) + Cl_2(g) \rightleftharpoons COCl_2(g)$.

Answer: $K_c = \frac{[COCl_2]}{[CO][Cl_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 49: State the $K_c$ expression for the reaction $C_2H_4(g) + H_2(g) \rightleftharpoons C_2H_6(g)$.

Answer: $K_c = \frac{[C_2H_6]}{[C_2H_4][H_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 50: If $K_c = 1.5$ for the reaction $A \rightleftharpoons B$, what is the value of $K_c$ for $B \rightleftharpoons A$?

Answer: $K_c = \frac{1}{1.5}$. For the reverse reaction, $K_c$ becomes the reciprocal of the original.

Flashcard 51: For $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, how does increasing pressure affect equilibrium?

Answer: Shifts towards $N_2O_4$. Higher pressure favors the side with fewer gas molecules (1 vs 2).

Flashcard 52: What is the effect of adding an inert gas at constant volume on the equilibrium of a reaction?

Answer: No effect. Inert gas doesn't participate and doesn't change partial pressures.

Flashcard 53: State the relationship between $K_p$ and $K_c$ for gaseous reactions.

Answer: $K_p = K_c(RT)^{\Delta n}$. Where $\Delta n$ is moles of gaseous products minus gaseous reactants.

Flashcard 54: For $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, how does increasing pressure affect equilibrium?

Answer: Shifts towards $N_2O_4$. Higher pressure favors the side with fewer gas molecules (1 vs 2).

Flashcard 55: For the reaction $2NO(g) + O_2(g) \rightleftharpoons 2NO_2(g)$, what is the $K_p$ expression?

Answer: $K_p = \frac{P_{NO_2}^2}{P_{NO}^2 P_{O_2}}$. Products over reactants using partial pressures, raised to coefficients.

Flashcard 56: If $[N_2] = 2M$, $[H_2] = 1M$, $[NH_3] = 0.5M$, find $Q_c$ for $N_2 + 3H_2 \rightleftharpoons 2NH_3$.

Answer: $Q_c = \frac{0.5^2}{2 \times 1^3}$. $Q_c = \frac{[NH_3]^2}{[N_2][H_2]^3} = \frac{0.5^2}{2 \times 1^3} = \frac{0.25}{2}$.

Flashcard 57: For the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, what is the expression for $K_p$?

Answer: $K_p = \frac{P_{SO_3}^2}{P_{SO_2}^2 P_{O_2}}$. Products over reactants using partial pressures, raised to coefficients.

Flashcard 58: What is the equilibrium expression for $H_2(g) + S(s) \rightleftharpoons H_2S(g)$?

Answer: $K_c = [H_2S]$. Solids are excluded from equilibrium expressions, only gases included.

Flashcard 59: How does a decrease in the concentration of $O_2$ affect equilibrium in $2SO_2 + O_2 \rightleftharpoons 2SO_3$?

Answer: Shifts left. Removing reactant shifts equilibrium to replace it via reverse reaction.

Flashcard 60: Determine the equilibrium constant $K_c$ for the reaction $2NO_2(g) \rightleftharpoons N_2O_4(g)$ given $[NO_2] = 0.5M$, $[N_2O_4] = 0.2M$.

Answer: $K_c = 0.8$. $K_c = \frac{[N_2O_4]}{[NO_2]^2} = \frac{0.2}{0.5^2} = 0.8$.

Flashcard 61: What is the effect of increasing temperature on the equilibrium position of an exothermic reaction?

Answer: Shifts towards reactants. Higher temperature opposes exothermic reactions, favoring the reverse direction.

Flashcard 62: Calculate $K_c$ for $H_2 + I_2 \rightleftharpoons 2HI$ with $[H_2] = 1M$, $[I_2] = 1M$, $[HI] = 2M$.

Answer: $K_c = \frac{4}{1}$. $K_c = \frac{[HI]^2}{[H_2][I_2]} = \frac{2^2}{1 \times 1} = 4$.

Flashcard 63: State the effect of a temperature decrease on an endothermic reaction's equilibrium position.

Answer: Shifts towards reactants. Lower temperature opposes endothermic reactions, favoring reactant formation.

Flashcard 64: Identify the expression for $K_c$ for $H_2O(l) \rightleftharpoons H^+(aq) + OH^-(aq)$.

Answer: $K_w = [H^+][OH^-]$. Auto-ionization of water uses $K_w$ notation for the equilibrium constant.

Flashcard 65: What is the equilibrium constant expression for $2H_2O_2(aq) \rightleftharpoons 2H_2O(l) + O_2(g)$?

Answer: $K_c = [O_2]$. Liquids are excluded from equilibrium expressions, only gases included.

Flashcard 66: If $[N_2] = 2M$, $[H_2] = 1M$, $[NH_3] = 0.5M$, find $Q_c$ for $N_2 + 3H_2 \rightleftharpoons 2NH_3$.

Answer: $Q_c = \frac{0.5^2}{2 \times 1^3}$. $Q_c = \frac{[NH_3]^2}{[N_2][H_2]^3} = \frac{0.5^2}{2 \times 1^3} = \frac{0.25}{2}$.

Flashcard 67: For the endothermic reaction $A \rightleftharpoons B$, what is the effect of increasing temperature?

Answer: Shifts towards $B$. Higher temperature favors endothermic reactions (heat-absorbing direction).

Flashcard 68: Find $K_c$ for the reaction $2A \rightleftharpoons B + C$ if $[A] = 0.5M$, $[B] = 1M$, $[C] = 1M$.

Answer: $K_c = \frac{1 \times 1}{0.5^2}$. $K_c = \frac{[B][C]}{[A]^2} = \frac{1 \times 1}{0.5^2} = 4$.

Flashcard 69: What is the effect of adding a product on the position of equilibrium?

Answer: Shifts left to form more reactants. Le Chatelier's principle: system responds by consuming the added product.

Flashcard 70: Identify the expression for $K_c$ for $H_2O(l) \rightleftharpoons H^+(aq) + OH^-(aq)$.

Answer: $K_w = [H^+][OH^-]$. Auto-ionization of water uses $K_w$ notation for the equilibrium constant.

Flashcard 71: Which factor does not affect the value of the equilibrium constant $K$?

Answer: Concentration of reactants or products. $K$ depends only on temperature, not concentrations at equilibrium.

Flashcard 72: Which factor does not affect the value of the equilibrium constant $K$?

Answer: Concentration of reactants or products. $K$ depends only on temperature, not concentrations at equilibrium.

Flashcard 73: For $2NO_2(g) \rightleftharpoons N_2O_4(g)$, what happens to $K_c$ if temperature is increased?

Answer: $K_c$ decreases. Higher temperature opposes exothermic reactions, decreasing $K_c$.

Flashcard 74: State the effect of adding a reactant on the equilibrium position.

Answer: Shifts right to form more products. Le Chatelier's principle: system responds by consuming the added reactant.

Flashcard 75: For $2NO_2(g) \rightleftharpoons N_2O_4(g)$, what happens to $K_c$ if temperature is increased?

Answer: $K_c$ decreases. Higher temperature opposes exothermic reactions, decreasing $K_c$.

Flashcard 76: What is the effect of pressure decrease on equilibrium of $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

Answer: Shifts left. Lower pressure favors the side with more gas molecules (4 vs 2).

Flashcard 77: What is the effect of a catalyst on the equilibrium constant $K$?

Answer: No effect. Catalysts only affect reaction rate, not equilibrium position or $K$.

Flashcard 78: State the effect of adding a reactant on the equilibrium position.

Answer: Shifts right to form more products. Le Chatelier's principle: system responds by consuming the added reactant.

Flashcard 79: For the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$, what is the expression for $K_p$?

Answer: $K_p = \frac{P_{SO_3}^2}{P_{SO_2}^2 P_{O_2}}$. Products over reactants using partial pressures, raised to coefficients.

Flashcard 80: For $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, how does increasing pressure affect equilibrium?

Answer: Shifts towards $N_2O_4$. Higher pressure favors the side with fewer gas molecules (1 vs 2).

Flashcard 81: For the reaction $C(s) + CO_2(g) \rightleftharpoons 2CO(g)$, write the $K_c$ expression.

Answer: $K_c = [CO]^2/[CO_2]$. Solid carbon is excluded, only gaseous species are included.

Flashcard 82: For $N_2O_4(g) \rightleftharpoons 2NO_2(g)$, how does increasing pressure affect equilibrium?

Answer: Shifts towards $N_2O_4$. Higher pressure favors the side with fewer gas molecules (1 vs 2).

Flashcard 83: Identify the expression for $K_c$ for $H_2O(l) \rightleftharpoons H^+(aq) + OH^-(aq)$.

Answer: $K_w = [H^+][OH^-]$. Auto-ionization of water uses $K_w$ notation for the equilibrium constant.

Flashcard 84: What is the equilibrium constant expression for $2H_2O_2(aq) \rightleftharpoons 2H_2O(l) + O_2(g)$?

Answer: $K_c = [O_2]$. Liquids are excluded from equilibrium expressions, only gases included.

Flashcard 85: What is the equilibrium expression for $H_2(g) + S(s) \rightleftharpoons H_2S(g)$?

Answer: $K_c = [H_2S]$. Solids are excluded from equilibrium expressions, only gases included.

Flashcard 86: What is the effect of increasing temperature on the equilibrium position of an exothermic reaction?

Answer: Shifts towards reactants. Higher temperature opposes exothermic reactions, favoring the reverse direction.

Flashcard 87: Identify the equilibrium expression for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.

Answer: $K_c = \frac{[NH_3]^2}{[N_2][H_2]^3}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 88: Which factor does not affect the value of the equilibrium constant $K$?

Answer: Concentration of reactants or products. $K$ depends only on temperature, not concentrations at equilibrium.

Flashcard 89: What happens to the equilibrium position when pressure is increased for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

Answer: Shifts towards $NH_3$. Higher pressure favors the side with fewer gas molecules (2 vs 4).

Flashcard 90: Find $K_c$ for the reaction $2A \rightleftharpoons B + C$ if $[A] = 0.5M$, $[B] = 1M$, $[C] = 1M$.

Answer: $K_c = \frac{1 \times 1}{0.5^2}$. $K_c = \frac{[B][C]}{[A]^2} = \frac{1 \times 1}{0.5^2} = 4$.

Flashcard 91: If $[N_2] = 2M$, $[H_2] = 1M$, $[NH_3] = 0.5M$, find $Q_c$ for $N_2 + 3H_2 \rightleftharpoons 2NH_3$.

Answer: $Q_c = \frac{0.5^2}{2 \times 1^3}$. $Q_c = \frac{[NH_3]^2}{[N_2][H_2]^3} = \frac{0.5^2}{2 \times 1^3} = \frac{0.25}{2}$.

Flashcard 92: Identify the equilibrium expression for the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$.

Answer: $K_c = \frac{[NH_3]^2}{[N_2][H_2]^3}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 93: What is the effect of a catalyst on the equilibrium constant $K$?

Answer: No effect. Catalysts only affect reaction rate, not equilibrium position or $K$.

Flashcard 94: Determine the equilibrium constant $K_c$ for the reaction $2NO_2(g) \rightleftharpoons N_2O_4(g)$ given $[NO_2] = 0.5M$, $[N_2O_4] = 0.2M$.

Answer: $K_c = 0.8$. $K_c = \frac{[N_2O_4]}{[NO_2]^2} = \frac{0.2}{0.5^2} = 0.8$.

Flashcard 95: What is the equilibrium constant expression for $2H_2O_2(aq) \rightleftharpoons 2H_2O(l) + O_2(g)$?

Answer: $K_c = [O_2]$. Liquids are excluded from equilibrium expressions, only gases included.

Flashcard 96: State the $K_c$ expression for the reaction $C_2H_4(g) + H_2(g) \rightleftharpoons C_2H_6(g)$.

Answer: $K_c = \frac{[C_2H_6]}{[C_2H_4][H_2]}$. Products over reactants, each raised to their stoichiometric coefficients.

Flashcard 97: Find $K_c$ for $A \rightleftharpoons 2B$ if $[A] = 1M$, $[B] = 0.5M$ at equilibrium.

Answer: $K_c = \frac{0.5^2}{1}$. $K_c = \frac{[B]^2}{[A]} = \frac{0.5^2}{1} = 0.25$.

Flashcard 98: Determine the equilibrium constant $K_c$ for the reaction $2NO_2(g) \rightleftharpoons N_2O_4(g)$ given $[NO_2] = 0.5M$, $[N_2O_4] = 0.2M$.

Answer: $K_c = 0.8$. $K_c = \frac{[N_2O_4]}{[NO_2]^2} = \frac{0.2}{0.5^2} = 0.8$.

Flashcard 99: What is the effect of pressure decrease on equilibrium of $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$?

Answer: Shifts left. Lower pressure favors the side with more gas molecules (4 vs 2).

Flashcard 100: If $K_c = 1.5$ for the reaction $A \rightleftharpoons B$, what is the value of $K_c$ for $B \rightleftharpoons A$?

Answer: $K_c = \frac{1}{1.5}$. For the reverse reaction, $K_c$ becomes the reciprocal of the original.