CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)
Problem
Consider the gaseous equilibrium H2(g)+I2(g)⇌2HI(g). A particulate diagram produced by a lab partner shows 20 purple diatomic molecules labelled H2, 20 red diatomic molecules labelled I2, and 40 purple-red heteronuclear molecules labelled HI. Closer inspection reveals that the purple diatomic molecules actually contain iodine atoms and the red diatomic molecules actually contain hydrogen atoms: the labels are reversed.
(1) Identify the labelling error in the diagram and explain why it would mislead someone analysing the equilibrium mixture.
(2) Describe how the mislabeled diagram could lead to an incorrect numerical value for the equilibrium constant when the particle counts are used in the equilibrium expression.
(3) Propose two best-practice guidelines students should follow to avoid such representational errors when constructing particulate diagrams for equilibrium systems.