C6: Dynamic Equilibrium and Reverse Reactions

• Reversible reactions are a type of chemical reaction where the products of the reaction can react to produce the original reactants.
• A larger volume of gas (more moles) has a smaller volume of gas (fewer moles).
• An increase in pressure decreases the yield of a reaction.
• A decrease in pressure increases the yield of a reaction.
• The direction of a reversible reaction can be changed by changing the conditions, for example, for a forwards reaction use hot conditions and for a reverse use cool.
• The symbol ⇌ is used to represent a reversible reaction.
• The Haber Process: hydrogen + nitrogen ⇌ ammonia is an example of a reversible reaction.
• If a reversible reaction is endothermic one way, it is exothermic in the opposite direction.
• The same amount of energy is transferred each way in a reversible reaction.
• When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in each direction.
• The relative amounts of all the reacting substances at equilibrium depend on the conditions of the reaction.
• If temperature is increased, equilibrium moves in the direction of the endothermic reaction, producing more product if the forwards reaction is endothermic and temperature is increased.
• If concentration of products is increased, the position of equilibrium shifts towards reactants, producing more reactant until equilibrium is reached again.
• If pressure is decreased, equilibrium will shift to side of equation with more moles of gas, producing more reactant.
• For a forwards reaction being exo/endothermic and yielding, an increase in temperature decreases yield of reaction, while a decrease in temperature increases yield of reaction.
• If concentration of reactants is increased, the position of equilibrium shifts towards products, producing more product until equilibrium is reached again.
• In gaseous reactions, an increase in pressure favours the reaction that produces the least number of molecules as shown by the symbol equation for that reaction.
• If temperature is decreased, equilibrium moves in the direction of the exothermic reaction.
• If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change, this is known as Le Chatelier's principle.
• If pressure is increased, equilibrium shifts to side of equation with fewer moles of gas, producing more product.
• If the concentration of one of the reactants or products is changed, the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.