A sealed 1.00 L flask at 298 K contains the gas–phase equilibrium N_2O_4(g) ; ; 2…
CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
A sealed 1.00 L flask at 298 K contains the gas–phase equilibrium
N2O4(g)⇌2NO2(g)ΔHfwd=+57kJmol−1
At equilibrium the partial pressures are
• PN2O4=0.40atm
• PNO2=0.80atm
Two separate stresses are applied in the order given below, and after each stress the system is allowed to return to equilibrium at 298 K.
1. An additional 0.10 atm of N2O4 is injected.
2. The volume of the flask is then suddenly reduced to one-half of its original value while the temperature remains constant.
Answer the following questions about the sequence of events.
(a) For the first stress, state the direction in which the equilibrium shifts and explain your reasoning in terms of the reaction quotient Q.
(b) After the system has re-established equilibrium following the first stress, the volume is halved. Predict the direction of the second equilibrium shift and justify your answer with reference to total gaseous moles on each side of the balanced equation.
(c) Compare the final partial pressure of NO2 after both stresses to its original value (greater than, less than, or equal to). Provide a concise justification that cites the cumulative effect of both stresses.