Hydrogen iodide is formed according to the gaseous equilibrium H₂(g) + I₂(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
Hydrogen iodide is formed according to the gaseous equilibrium
H₂(g) + I₂(g) ⇌ 2 HI(g)
A rigid 4.00 L vessel at 700 K contains an equilibrium mixture with partial pressures PH2=0.30atm, PI2=0.30atm, and PHI=1.20atm. Helium gas is then injected into the vessel until the total pressure doubles, while the temperature and volume remain constant.
(a) Show quantitatively that the reaction quotient Qp after the helium addition is equal to the original equilibrium constant. Explain each step in your reasoning.
(b) Based on your result in part (a), state and justify whether any net shift in the position of equilibrium will occur after the helium addition.
(c) Describe qualitatively how the partial pressure of each reacting species and the total pressure change between the moment just before helium injection and the final state after re-equilibration.