14. Chemical Equilibrium   Previous PageNext Page
       Examples of Equilibrium Constants

Combustion of hydrogen

The water reaction is even more extreme. The reaction is

(g) + (g) (g)
G = -109.3 kcal per 2 moles of

and the equilibrium-constant expression is

Even without putting pencil to paper we can see that there should be infinitesimal amounts of hydrogen and oxygen gases at equilibrium. The equilibrium mixture should be nearly pure water. As the large negative also indicates, the forward reaction will be very spontaneous.

This equilibrium-constant expression, unlike that for HCl, has different powers of concentration in the numerator and denominator. If concentrations are specified as partial pressures in atmospheres, then will have units of atm / atm = atm.

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