Unformatted text preview: tants and vice versa. When the rate of the forward reaction is
equal to the rate of the reverse reaction, the amounts of the chemical species remain constant, and the system is
in a state of e quilibrium. Anything that changes a variable associated with the equilibrium induces a s tre s s on
the system. If a stress is applied, the system will shift to accommodate and offset this stress, and a new
equilibrium condition will be established. This principle was first articulated by a French chemist, Henri- Louis
Le Châtelier, in 1884, and it still bears his name. His concise expression of the principle is:
If a stress is applied to a system at equilibrium, the system will respond by shifting in the direction that
reduces the stress.
As an example of a stress, consider the addition of more ammonia to the equilibrium in equation 3
4 NH3(g) + 3 O2(g) 2 N2(g) + 6 H2O(g)
. To reduce this stress, some of the added ammonia reacts with oxygen to produce more products (nitrogen and
water). A new equilibrium co...
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