Dynamic Equilibrium — rates, concentrations and Kc

Reaction

Q_c expression

Preset

Temperature & K_c

T350 K

ΔH−45 kJ mol⁻¹

K_c

2.80

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Concentration vs timeAmounts level off at equilibrium

Rate vs timeForward and reverse rates become equal

forward

reverse

The K_c expression vs timeRises or falls onto the K_c line as the system reaches equilibrium

Q_c (current)

K_c = k_f/k_r

Model. Elementary kinetics assumed, so orders equal the stoichiometric coefficients: rate_f = k_f·∏[reactant]^coeff, rate_r = k_r·∏[product]^coeff. At equilibrium the rates are equal, which rearranges to K_c = k_f/k_r. The plotted Q_c is that same expression at the current concentrations — equal to K_c only once equilibrium is reached. Rate-constant units are illustrative.

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Temperature & Kc

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Temperature & K_c