Answers to Practise Questions (Basic) â Rate of Reaction
Transcription
Answers to Practise Questions (Basic) â Rate of Reaction
Answers to Practise Questions (Basic) – Rate of Reaction Practise questions (Basic) are designed to ensure that students are aware of the basic concepts of the topic. This should be the first step that students undertake while revising for their chemistry examination. For the O Level examination, these basic concepts will be tested although questions will not be straight forward and students will need to be able to apply these concepts to solve the questions. (1): Explain why increasing the (i) concentration (ii) temperature of reacting particles increases the rate of reaction. Increasing the concentration increases the number of reacting particles per unit volume. This increases the number of collisions between reacting particles. As a result, the number of effective collisions increases. Thus, rate of reaction increases with increasing concentration. When the temperature is increased, the reacting particles have more energy and move faster. They collide more frequently and with energy greater than the activation energy. This increases the number of effective collision. Thus, rate of reaction increases when the temperature is increased. (2): Explain why decreasing the particle size of the reactants increases the rate of reaction. When the particle size is decreased, there is an increased surface area exposed to collision with other reactants. Thus, the number of collisions and effective collisions between reacting particles increase. This increases the rate of reaction. (3): Explain why the usage of catalyst increases the rate of reaction. The usage of catalyst decreases the activation energy of the reaction. As a result, there ©Breeze Education 2015 breeze-education.com Page 1 are more reacting particles with energy greater than the activation energy. Thus, the frequency of effective collisions increase. This increases the rate of reaction. (4): State whether addition of catalyst increases the amount of energy release during a chemical reaction. Catalyst does not alter the enthalpy change of a chemical reaction. (5): Describe briefly how the rate the below reactions could be monitored: (a): Calcium carbonate with hydrochloric acid Carbon dioxide is produced during the reaction. The mass of the reacting mixture could be monitored during the reaction. As carbon dioxide is released during the reaction, the mass of the reacting mixture would decrease. By monitoring, the change in mass of the reacting mixture, the rate of reaction could be monitored. (b): Sodium thiosulfate with hydrochloric acid producing sodium chloride, water, sulfur dioxide and sulfur Sulfur is produced during the reaction and this could produce a suspension which could make the flask opaque when view from the top. By monitoring the time taken for the view to be blocked, the rate of reaction could be monitored. (c): Decomposition of hydrogen peroxide producing water and oxygen gas As oxygen gas is produced during the reaction; the reaction could be monitored by measuring the volume of gas that is released. (6): Give two examples of catalysts and their uses in industry Iron is used in the production of ammonia in the Haber process Nickel is used in the addition reaction of alkene producing alkane ©Breeze Education 2015 breeze-education.com Page 2 About Breeze Education: Breeze Education offers chemistry tuition to O Level Students. Tuition classes are conducted in small group to facilitate active discussion and consultation. Chemistry is taught in a way to facilitate easy understanding of the topic. Students are also honed on their revision techniques so that they can improve faster over a shorter period of time. Tuition sessions are planned and taught by Dr Francis who has a PhD in Biomedical Science from National University of Singapore. Lesson is conducted in Yishun with direct bus connecting to Sembawang and Woodlands. ©Breeze Education 2015 breeze-education.com Page 3
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