This practice test covers the key concepts in AP Chemistry Unit 6: Thermodynamics and Equilibrium. Remember to consult your textbook and notes for a thorough review before attempting these questions. Good luck!
Section 1: Multiple Choice
Instructions: Choose the best answer for each multiple-choice question.
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Which of the following statements is true regarding a spontaneous process? a) It always occurs rapidly. b) It always releases heat. c) It always increases the entropy of the system. d) It always proceeds in the direction of lower Gibbs free energy.
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What is the standard free energy change (ΔG°) for a reaction at 298 K if the equilibrium constant (K) is 10? (R = 8.314 J/mol·K) a) A large positive value b) A large negative value c) Approximately zero d) Cannot be determined without more information
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Consider the reaction: A(g) + B(g) <=> C(g). Increasing the pressure on this system at equilibrium will: a) Shift the equilibrium to the left. b) Shift the equilibrium to the right. c) Have no effect on the equilibrium. d) Increase the value of K.
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Which of the following is NOT a state function? a) Enthalpy (H) b) Entropy (S) c) Gibbs Free Energy (G) d) Heat (q)
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What is the effect of increasing temperature on an exothermic reaction at equilibrium? a) The equilibrium shifts to the left. b) The equilibrium shifts to the right. c) The equilibrium constant (K) increases. d) The equilibrium constant (K) remains unchanged.
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A reaction with a positive ΔH and a positive ΔS will be spontaneous under which conditions? a) Never b) Always c) At high temperatures d) At low temperatures
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What is the relationship between Gibbs Free Energy (ΔG), enthalpy (ΔH), entropy (ΔS), and temperature (T)? a) ΔG = ΔH + TΔS b) ΔG = ΔH – TΔS c) ΔG = ΔS – TΔH d) ΔG = TΔS – ΔH
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The equilibrium expression for the reaction: 2A(g) + B(s) <=> 3C(g) is: a) K = [C]³/[A]²[B] b) K = [C]³/[A]² c) K = [A]²[B]/[C]³ d) K = [A]²/ [C]³
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A catalyst will affect which of the following aspects of a reversible reaction? a) Equilibrium constant (K) b) ΔG c) Activation energy d) ΔH
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Le Chatelier's Principle states that: a) The rate of a reaction is proportional to the concentration of reactants. b) A system at equilibrium will shift to relieve stress. c) The equilibrium constant is independent of temperature. d) The entropy of the universe is always increasing.
Section 2: Free Response
Instructions: Answer the following free-response questions completely and show all your work.
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A reaction has a ΔH of +50 kJ/mol and a ΔS of +150 J/mol·K. Calculate the ΔG at 298 K and 500 K. Is the reaction spontaneous at either temperature? Explain your answer.
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Consider the reaction: N₂(g) + 3H₂(g) <=> 2NH₃(g).
- Write the equilibrium expression for this reaction.
- Predict the effect on the equilibrium position if the pressure is increased.
- Predict the effect on the equilibrium position if more hydrogen gas is added.
- Predict the effect on the equilibrium position if the temperature is increased (assuming this is an exothermic reaction).
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Explain the difference between ΔG and ΔG°. How are they related?
This practice test provides a good starting point for your review of AP Chemistry Unit 6. Remember to focus on understanding the underlying principles and concepts, not just memorizing formulas. Good luck on your exam!
