Simple Equilibria

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  • Created by: zoolouise
  • Created on: 17-04-16 17:20


Reversible Reactions

  • A reversible reaction is one that can go in either direction depending on the conditions

Reactions don't only move in the forward direction, some also go backwards and products change back into reactants. These reactions are called reversible and we use a special symbol in the equations (⇌)

A reversible reaction you are familiar with is water. If you lower the temperature of water below 0 it freezes to ice, if the ice is allowed to reach room temperature it melts back to water

Water  Ice or H2O(I)  H2O(s)

Blue coppier (II) sulfate crystals have the formula CuSO4.5H2O, the water is caled water of crystallisation. When the water is heated, the water of crystallisation is given off as steam leaving a white powder called anhydrous copper (II) sulfate. When water is added to the ***********, the owder gets hot and turns blue. 

CuSO4.5H2O ⇌ cUso4 + 5h2o

The Haber process is a well-known industrial example:

N2(g) + 3H2(g) ⇌ 2NH3(g)

Dynamic equilbria 

  • Dynamic equilibrum is when the forward and reverse reactions occur at the same rate.

Equilibrum is a term used to denote balance. The two main types are static and dynamic. An example of dynamic equilibrum is dissolving an ionic compound in water. When copper(II) sulfate crystals are added to water, the crystals dissolve and the solution turns blue. The more copper(II) sulfate added, the deeper the blue colour. When no more dissolves and copper(II) sulfate crystals remain in the solution, the solution has become saturated and the intensity of the blue colour remains constant.

At this point the solution is in equilibrium with the undissolved solid. Although nothing seems to be happening since the concentration of the saturated soliution remains the same, the copper(II) solution is still dissolving. This can be proved by using radioactive tracers. Dynamic equilibra can also develop during chemical changes. The balance of reactants and products at equilibrum is called the equilibrium mixture. If the equilibrum mixture contains mostly products and hardy any reactants, we say that the reaction has gone to completion. If the equilibrium mixture consists mostly of reactants and hardy any products, we say that the reaction doesn't happen under these conditions.

At equilibrium there's no observable change; the properties that we can see or measure remain constant. These are called macroscopic properties. The system is in constant motion - the dyanmic change happening at a molecular level. The reacts and products must be in contact at all time  so a closed system is needed for this to happen. When equilibrium is estabalished in a chemica process, normally the concentrations of the reactans and products change rapidly at first and then reach stedy values. At this point the reactants are being converted into producst at exactly the same rate as products are being converted into reactants.

Position of equilibrium

  • Position of equilibrum is the proportion of products to reactants in an equilibrium mixture
  • Le Chatelier's principle states that if


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