NJC Class Quiz 4 Kinetics QP

National Junior College SH1 H1 Chemistry 1 SH1 Exit Quiz (Reaction Kinetics) Name: ____________________________________ Duration: 20 min 1 Sucrose is a sugar produced in plants such as sugarcane and sugar beet where it is extracted and refined for use as a sweetener in food and beverage. In sucrose, the bond between the monomers glucose and fructose can be broken via a hydrolysis reaction with water. The hydrolysis is so slow that a solution of sucrose can be stored for a long period of time at room temperature with negligible change. (a) Enzymes like sucrase have specific activity. When a very small amount of sucrase is added to a solution of sucrose, however, the hydrolysis reaction will proceed rapidly. (i) Explain what is meant by the term specific activity of an enzyme. ................................ ................................ ................................ ............................... ................................ ................................ ................................ ........................... [1] The graph in Fig. 1.1 shows how the initial rate varies with sucrose concentration for the hydrolysis reaction where a very small amount of sucrase was added. Fig. 1.1 (ii) “At very high concentrations, the order of reaction with respect to [sucrose] is 1.” Comment on the validity of this statement and explain your answer using Fig. 1.1. ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ........................... [1] initial rate of reaction [sucrose] 11

National Junior College SH1 H1 Chemistry 2 (iii) Using a Boltzmann distribution curve, explain why the addition of sucrase increases the rate of the hydrolysis reaction. ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ............................... ................................ ................................ ................................ ........................... [3]

National Junior College SH1 H1 Chemistry 3 (b) The hydrolysis reaction of sucrose can also be accelerated with acids such as hydrochloric acid. The hydrolysis reaction of sucrose with HC l was studied at constant temperature via a series of experiments. experiment [sucrose] / mol dm−3 [HCl] / mol dm−3 rate / mol dm−3 min−1 1 0.10 1.0 2.0  10−5 2 0.20 1.0 4.0  10−5 3 0.30 2.0 1.2  10−4 (i) Deduce the order of reaction for sucrose and HCl. Hence, give the rate equation for the reaction. [3]

National Junior College SH1 H1 Chemistry 4 In each experiment, concentration of HC l remained effectively constant throughout the hydrolysis reaction. (ii) Complete Fig. 1.2 to show how the concentration of sucrose varies with time, at constant temperature for experiment 1 where the initial concentration of sucrose used was 0.100 mol dm−3. Label any important features on Fig. 1.2. Fig. 1.2 [2] 2 The age of rock samples can be calculated using Uranium -Lead dating. 235U is an unstable isotope which decays into 207Pb. This nuclear reaction obeys first -order kinetics with a half-life of 710 million years. The decay can be summarised by the following equation: 235U → 207Pb + other decay products A rock sample has a 235U : 207Pb ratio of 1 : 15. Assuming that all the 207Pb detected is formed from the decay of 235U, what is the age of the rock sample? A 710 million years C 2130 million years B 1420 million years D 2840 million years [sucrose] / mol dm−3 time / min 0.100 0