5 Steps to a 5 AP Chemistry

AP Chemistry Practice Exam 2  335

AP Chemistry Practice Exam 2—Free Response

Time—1 hour and 35 minutes

Answer the following questions in the time allowed. You may use the tables at the

back of the book. Write the answers on a separate sheet of paper.

Part A. Time — 55 minutes

You may use a calculator for part A.

Question 1.

The value of Kpfor the above equilibrium is 0.262 at 1270 K.

(a) Write the equilibrium constant expression for the above equation.

(b) Determine the value of Kcfor the above equation at this temperature.

(c) What is the value of Kpfor the following equilibrium at 1270 K? Justify your answer.

(d) Methane gas is introduced to a rigid container. The container is heated to 1270 K, and the initial par-

tial pressure of the methane is 0.200 atm. What is the partial pressure of H 2 once equilibrium has been

established?

(e) In a separate experiment, a container with the initial equilibrium established is heated to 1350 K. At

the higher temperature, the amount of CH 4 present has decreased, and the amount of H 2 present has

increased. Is the initial equilibrium endothermic or exothermic? Justify your answer.

(f ) A small amount of carbon is introduced to a rigid container that is already at equilibrium. What

changes, if any, would there be in the partial pressure of H 2? Justify your answer.

Question 2.

The above reaction occurs in basic solution. The following data were obtained from a series of experiments.

INITIAL CONCENTRATIONS INITIAL RATE

(MOLARITIES) (mol/L s)

[I-] [CIO-] [OH-]

Experiment 1 0.200 0.200 0.200 1.22

Experiment 2 0.400 0.200 0.200 2.44

Experiment 3 0.200 0.400 0.200 2.44

Experiment 4 0.200 0.200 0.400 0.610

Answer the following questions.

(a) Determine the order of the reaction for I–, ClO–, and OH–. Justify your answers.

(b) Write the rate law for the reaction.

I aq−−−−()+→+ClO aq()IO aq()Cl aq()

CH g 42 ()C s()+ 2 H g()

Cs +2H g() 24 ()CH g()

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