Hydrogen iodide decomposes according to
2HI(g)⇌H2(g)+I2(g)
At 700 K the equilibrium constant Kp is 1.70.
A 5.00 L reaction vessel at 700 K is initially charged with 0.800 mol HI, 0.100 mol H2, and 0.040 mol I2.
Immediately after sealing, an additional 0.200 mol of I2 is injected, and the temperature is held constant while the reaction is allowed to attain equilibrium.
Subsequently, without changing the temperature, the vessel volume is suddenly compressed to 2.50 L, and the system again comes to equilibrium.
Answer the following questions regarding the two successive disturbances.
(a) For the initial mixture before any I2 is added, determine whether the system is at equilibrium. Justify mathematically.
(b) After the I2 injection, calculate the value of the reaction quotient Qp and state the direction of net reaction required to restore equilibrium.
(c) Compute the equilibrium partial pressures of all species after the first disturbance has been resolved.
(d) Using the equilibrium state obtained in part (c) as a new starting point, evaluate Qp immediately after the volume is halved, and determine the direction in which the reaction will proceed.
(e) Calculate the final equilibrium partial pressures of each species after the compression and comment on how the total pressure compares with the value just before the compression step.