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Chemical Equilibrium
Dr G Mnguni
Mangosuthu University of Technology
Department of Environmental Health
Academic year – 2020s

Lesson objectives
´ To understand what is meant by a chemical equilibrium
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´ To gain an understanding of which factors affect an equilibrium and how
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There is no observable change in the properties of the
system
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´ There is no net change in concentrations of reactants and
products
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´ Not equal concentrations, equal opposite rates
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All
particles are at rest
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g
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,
pressure changes), it will respond to restore a new equilibrium
state
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´ A catalyst affects the rate of a reaction but doesn’t shift
equilibrium, it only makes a reaction reach equilibrium
faster by lowering the activation energy
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´ aA + bB ↔ cC + dD
´ Rate = -k1 [A]a[B]b = k1[C]c[D]d
´ When the rate = 0, then A, B, C & D are at equilibrium
with each other
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Gibb’s free energy
´ Dynamic equilibrium – useful in predicting whether the
forward or reverse reaction is spontaneous of nonspontaneous
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´ What is Gibbs free energy?
´ Formation of 1 mole of a substance in it’s standard state (1 bar,
25 degrees)

Gibb’s free energy contd
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´ When Q < K, more reactants are present initially than at
equilibrium = equilibrium shifts towards products
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Pressure
´ Adding an inert gas to a constant volume mixture effects pressure but partial
pressures remain the same so the equilibrium conditions are not affected
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2
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´ Endothermic reaction – requires/consumes heat
´ Increasing temp – shift equilibrium in the direction of endothermic reaction
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3
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´ Makes reaction reach equilibrium faster
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Concentration
´ The concentration of reactants and products affects the
reaction
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