 Solution

ID: past-exam-of-the-chemistry-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2025/4/a/i/solution

a_{i} = [i] / c^{\circ}

K_{a} = \frac{a _{H^{+}} a _{H N_{2} O_{2}^{-}}}{a _{H_{2} N_{2} O_{2}}} = \frac{[ H ^{+} ] [ H N _{2} O _{2}^{-} ]}{[ H _{2} N _{2} O _{2} ] c ^{\circ}}, c^{\circ} = 1 mol L^{- 1} .

The factor

c^{\circ}

makes the equilibrium constant compatible with

Δ_{r} G^{\circ} = - RT ln K_{a}

c^{\circ}

is used instead, it has concentration units and its numerical value is identical only when the standard concentration is expressed as

1 M

 New to topics? Read the docs here!