Rate of reactions

• The rate of a chemical reaction can be found by measuring the quantity of reactant used or the quantity of product formed over time.
• Increasing concentration of reactants in solution or pressure of reacting gases increases the frequency of collisions and rate of reaction.
• Reversible reactions can occur, with the forward and backward reactions happening at the same rate at equilibrium.
• The quantity of reactant or product can be measured by mass in grams or volume in cm3.
• Factors affecting rates of chemical reactions include concentrations of reactants, pressure of reacting gases, surface area of solid reactants, temperature, and presence of a catalyst.
• Increasing surface area, temperature, or using a catalyst increases the rate of reaction.
• Catalysts increase the rate of reaction by providing a different pathway with lower activation energy.
• The units of rate of reaction can be given as g/s or cm3/s.
• If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction (they are reversible/opposites). The same amount of energy is transferred in each case.
• The following reversible reaction occurs: The reaction that makes C and D is exothermic. What happens if we heat up A and B?

  A+B->C+D

  <-

  We will get less C and D
• What is meant by a reversible reaction?

  The products of a reaction can react to produce the original reactants.
• What needs to happen for equilibrium to be reached?

  Closed system; apparatus prevents the escape of reactants and products.
• What can be said about the amount of energy being transferred in a reversible reaction?

  Same amount of energy is transferred in both directions.
• What is meant by the term ‘collision theory’?

  Explains how factors affect the rate of reaction.
• What happens to the gradient of a line if the rate of reaction is increased?

  Becomes steeper