# Question 6

Pure hydrogen iodide gas, HI(g), of concentration 1 mol∙dm-3 , is sealed in a 500 cm3
container at temperature T. The reaction reaches equilibrium according to the following balanced equation:

6.1 Define the term chemical equilibrium. (2)

6.2 The graph below shows how the concentrations of the reactant and products vary with time during the reaction.

6.2.1 Which ONE of the curves, X or Y, represents the changes in the concentration of the products? Give a reason for the answer. (2)

6.2.2 How does the rate of the forward reaction compare to that of the reverse reaction at t = 4 minutes? Choose from HIGHER THAN, LOWER THAN or EQUAL TO. (1)

6.3 The equilibrium constant, Kc, for the reaction is 0,04 at temperature T.
Calculate the number of moles of iodine, I2(g), present at time t = 6 minutes. (9)

6.4 The graph below shows how the rates of the forward and reverse reactions change with time.

The temperature of the container is increased at t = 10 minutes.
6.4.1 Which reaction(s) show(s) an increase in rate at t = 10 minutes?
Choose from FORWARD, REVERSE or BOTH FORWARD AND REVERSE. (1)

6.4.2 Is the heat of reaction (∆H) for this reaction POSITIVE or NEGATIVE? Fully explain the answer. (4)
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