The rate and extent of chemical change

• Activation energy


  The minimum amount of energy that particles must collide with to react
• Catalyst

  Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. They are not used up during the reaction
• Collision theory


  According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
• If the concentration of a reactant is increased


  More products will be formed until equilibrium is reached again
• If the concentration of a product is decreased


  More reactants will react until equilibrium is reached again
• An increase in pressure


  Causes the equilibrium position to shift towards the side with the smaller number of molecules
• A decrease in pressure

  Causes the equilibrium position to shift towards the side with the larger number of molecules
• If the temperature of an equilibrium system is increased

  The relative amount of products at equilibrium increases for an endothermic reaction and decreases for an exothermic reaction
• Increasing the concentration of reactants in solution

  Means the reacting particles will be closer together, so they will collide more often resulting in a higher rate of successful collisions and a faster rate of reaction
• Increasing the pressure of gaseous reactants

  Means the reacting particles will be closer together, so they will collide more often resulting in a higher rate of successful collisions and a faster rate of reaction
• Increasing the surface area of the reactants

  Means there are more exposed reacting particles, so there are more frequent successful collisions and the rate of reaction increases
• Increasing the temperature


  Means the particles will have more kinetic energy and move faster, resulting in more frequent collisions and a larger proportion of particles having at least the activation energy, so the rate of reaction increases
• Equilibrium


  When a reversible reaction occurs in apparatus which prevents the escape of reactants and products, equilibrium is reached when the forward and reverse reactions occur at exactly the same rate
• Le Chatelier's Principle


  If a reaction at equilibrium is subjected to a change in concentration, temperature or pressure, the position of equilibrium will move to counteract the change
• Rate of reaction


  The measure of the amount of product formed or reactant used over time. The units of rate of reaction may be given as g/s, cm3/s or mol/s
• Reversible reaction

  Reactions in which the products from the reaction can react together to form the original reactants. The direction of reversible reactions can be changed by changing the conditions