or The quantity of reactant or product can be measured by the mass in grams, by a volume in cm3 or by an amount in moles. The units of rate of reaction may be given as g/s, cm3/s or mol/s. Draw and interpret graphs showing the quantity of product formed or quantity of reactant used up against time. Draw tangents to the curves on graphs and use the slope of the tangent as a measure of the rate of reaction. (HT only) Calculate the gradient of a tangent to the curve on these graphs as a measure of rate of reaction at a specific time. MS 1a, 1c, 1d, 4a, 4b, 4c, 4d, 4e Extended writing: write instructions to another student how to calculate the mean rate of reaction. Explain what is meant by the units: g/s cm3/s mol/s. Use the results and graph to determine the mean rate of reaction. A similar reaction can be done with magnesium and hydrochloric acid. 5.6.1.2 Factors affect the rates of chemical reactions include: the concentrations of reactants in solution, the pressure of reacting gases, the surface area of solid reactants, the temperature and the presence of catalysts. Be able to recall how changing these factors affects the rate of chemical reactions. WS 2.1, 2.2, 2.3, 2.4, 2.6, 2.7 MS 1a, 1c, 1d, 2a, 2b, 4a, 4b, 4c, 4d, 4e 2 Extended writing: explain the effect on the rate of reaction of the following factors: concentration pressure surface area temperature catalyst. Required practical 11: investigate how changes in concentration affect the rates of reactions by a method involving measuring the volume of a gas produced and a method involving a change in colour or turbidity. Video clips: YouTube:
Use graphs of data obtained from concentration reactions to explain what occurs as the reaction proceeds. This should be an investigation involving developing a hypothesis. AT skills covered by this practical activity: 1, 3, 5 and 6. This topic offers opportunities for practical work and investigations in addition to required practical 11, by changing temperature and surface area of reactants and use of catalysts. 5.6.1.3 Collision theory explains how various factors affect rates of reactions. According to this theory, chemical reactions can occur only when reacting particles collide with each other and with sufficient energy. The minimum amount of energy that particles must have to react is called the activation energy. Predict and explain using collision theory the effects of changing conditions of concentration, pressure and temperature on the rate of a reaction. Predict and explain the effects of changes in the size of pieces of a reacting in terms of 1 Describe collision theory. Use collision theory to explain the change in rate of reaction in terms of particle behaviour for: concentration pressure surface area temperature catalyst. Video clips YouTube: BBC Bitesize
Increasing the concentration of reactants in solution, the pressure of reacting gases, and the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction. Increasing the temperature increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction. surface area to volume ratio. Use simple ideas about proportionality when using collision theory to explain the effect of a factor on the rate of a reaction. WS 1.2 MS 1c, 5c 5.6.1.4 Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts. Enzymes act as catalysts in biological systems. Catalysts increase the rate of reaction by providing a different pathway for the reaction that has activation energy. Be able to identify catalysts in reactions from their effect on the rate of reaction and because they are not included in the chemical equation for the reaction. Be able to explain catalytic action in terms of activation energy. Students do not need to know the names of catalysts other than 1 Define the term activation energy. Identify advantages of using catalysts in industrial reactions eg reducing costs. Explain the effect of using a catalyst on the activation energy. Research different catalysts and uses in industry. Research catalytic converters. An opportunity to investigate the catalytic effect of adding different salts to a reaction such as the decomposition of hydrogen peroxide. AT 5 Video clip YouTube: