#LeChateliersprinciple

#Chemistry

#RateOfReaction

Introduction

• The relative amounts of all the reactants and products at equilibrium depend on the conditions of the reaction

  • This balance is framed in an important concept known as Le Chatelier's Principle,

  • This principle states that when a change is made to the conditions of a system at equilibrium, the system automatically moves to oppose the change

  • The principle is used to predict changes to the position of equilibrium when there are changes in:

    • Temperature

    • Pressure 

    • Concentration

  • Knowing the energy changes, states and concentrations involved allows us to use the principle to manipulate the outcome of reversible reactions

  • For example, if pressure is increased, the position of equilibrium moves in the direction which has the smallest amount of gaseous molecules

  • The position of equilibrium is said to shift to the right when the forward reaction is favoured

    • This means that there is an increase in the amount of products formed

  • The position of equilibrium is said to shift to the left when the reverse reaction is favoured

    • So, there is an increase in the amount of reactants formed

How temperature affects equilibrium

• We can predict the effect of changes in temperature on systems in equilibrium

  • To make this prediction it is necessary to know whether the reaction is exothermic or endothermic

• If the temperature is raised:

  • The yield from the endothermic reaction increases

  • The yield from the exothermic reaction decreases

• If the temperature is lowered:

  • The yield from the endothermic reaction decreases

  • The yield from the exothermic reaction increases

• When a change in temperature is made to a system, the system will oppose the change

  • E.g. If the temperature is increased, the system will oppose the change by decreasing the temperature

  • It will do this by favouring the endothermic reaction

The effects of temperature on equilibrium 

• Increase in temperature - Equilibrium moves in the endothermic direction to reverse the change

• Decrease in temperature - Equilibrium moves in the exothermic direction to reverse the change 

How pressure affects equilibrium

• Changes in pressure only affect reactions where the reactants or products are gases

• We can predict the effect of changes in pressure on systems in equilibrium

  • To make this prediction, the balanced symbol equation must be known

The effects of pressure on equilibrium

• Increase in pressure - Equilibrium shifts in the direction that produces the least number of molecules

• Decrease in pressure - Equilibrium shifts in the direction that produces the greatest number of molecules

How concentration affects equilibrium

• The effect of changing concentration can be thought of as a balance, with the reactants on the left and the products on the right

  • If the concentration of a reactant increases, then the equilbrium shifts to the right to balance this balance

The effects of concentration on equilibrium

• Increase in concentration of a reactant - Equilibrium shifts to the right

• Decrease in concentration of a reactant - Equilibrium shifts to the left 

• Increase in concentration of a product - Equilibrium shifts to the left 

• Decrease in concentration of a product - Equilibrium shifts to the right