��The experiments were made at 10*2° with solutions which were 0*02485 normal with respect to ethyl acetate and sodium hydroxide.
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��Velocity in Heterogeneous Sjrstems.— In the preceding chapter it was pointed out that the equilibrium of a system of molecules is to be regarded as " mobile." The state of equilibrium is therefore attained in a chemical system when the two reactions proceeding in opposite directions have the same velocity. If the velocity of decomposition of the ester be represented by the formula —
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��- '^^e»ter ^water ^ ^alcohol ^add.
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��the equilibrium constant of the ester-hydrolysis, K, is equal to the quotient of the two velocity constants —
��It has been found by the study of vaporisation and solution that the relationship between velocity and equilibrium is just as simple in heterogeneous systems.
Equilibrium is attained between liquid and its vapour when the maximum tension P of the liquid is equal to the partial pressure ip of its molecules in the vapour space, i.e. when P ^ p. The rate of evaporation is at every moment proportional to the difference between these two values, i.e. it is equal to k(P — p),
Noyes and Whitney Q) have found that the rate of
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