Sometimes gaseous equilibria can appear so mathematical that students lose a sense of why finding values of K_p is useful. It's well worth asking them what the actual value of K_p tells us in terms of the composition of the equilbrium mixture. This is particularly important in some industrial processes. We will explore this in greater detail in topic 7 (Equilibria in industry).

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K _p for the Haber process, the synthesis of ammonia from hydrogen and nitrogen, is 7.76 x 10^–5 atm^–2 at 700 K. What does this value indicate about the composition of the equilibrium mixture at ths temperature?

The equilibrium mixture contains more reactants than products.

K _p for the conversion of SO₂ to SO₃ in the Contact process for the manufacture of sulfuric acid is 3.0 x 10⁴ atm^–1 at 700 K. What does this value indicate about the composition of the equilibrium mixture at this temperature?

The equilibrium mixture contains more products than reactants

K _p for the equilibrium H₂(g) + I₂(g) _∏ 2HI(g) is 54 at 700 K. What can you say about the equilibrium mixture at this temperature?

The equilibrium mixture contains similar concentrations of reactants and products.