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3.1.6 Equilibria (Equilibrium constant Kc for homogeneous systems…
3.1.6 Equilibria
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Reversible Reactions
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Equilibria Mixture: the mixture of reactants and products formed when a reversible reaction is allowed to proceed in a closed container until no further change occurs; forward and backward reactions are proceeding at the same rate
A + B ⇌ C + D
At start of reaction, forward rate is fast as there is a lot of the reactants A and B; there is no reverse reaction because there is no products (C and D) yet
concentrations of C and D start to build up as forward reaction progresses; reverse reaction speeds up; concentration of A and B decrease at same time
equilibria is reached when same number of particles are in forward reaction, as in reverse reaction
Dynamic Equilibria: a situation in which the composition of a constant concentration reaction does not change because both forward and backward reactions are proceeding at the same rate
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Le Chatelier’s principle
Le Chatelier's principle can be used to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions.
A catalyst does not affect the position of equilibrium, as they provide an alternative route for the reaction, with lower activation energy
If a system at equilibria is disturbed, the equilibrium moves in the direction which tends to reduce the disturbance
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Reactions in industry
compromise temperature may be used; need to have fast rate of reaction, but also need high yield
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