10.1.1 Dynamic equilibrium and reversible reactions

• Reversible reactions refer to reactions in which the products of a reaction can react together to form the original reactants. They are represented using a double arrow.
• In a reaction system, one reaction will be endothermic and the opposite will be exothermic.
• Reversible reactions will eventually reach a state of dynamic equilibrium. At this stage : the rate of the forwards reaction equals the rate of the backwards reaction and the concentration of the products and reactants remains constant.
• Dynamic equilibrium can only occur in closed systems where no substances can get in or out, and the reaction must be reversible.
• When the forwards reaction begins, the reactants begin to react to form the products of the reaction. As this occurs, the concentration of the reactants is decreasing, so the rate of the forwards reaction also decreases. Eventually, the products begin to decompose (the backwards reaction), and the concentration of the products continues to increase due to the forwards reaction. This causes the rate of the backwards reaction to increase, and eventually the rate of the forwards and backwards reaction is equal.
• Le Chatelier's Principle is used to predict how an equilibrium mixture will change if the reaction conditions are altered. It states that 'when a system is subject to change, the system will alter to lessen the effect of that change'.
• Le Chatelier's Principle can be used in industry through altering the reaction conditions to maximise yield of a desired product.