[CHEM] Chapter 6.1 - Rate of Reaction

1 DARRELL ER (COPYRIGHTED) © TOPIC 6.1: RATE OF REACTION DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE • Relatively okay chapter • 5 key concepts - Size of reactant particles - Concentration of reactants - Pressure applied - Temperature of mixture - Use of catalysts • Very much interlinked with Energy Changes • Energy profile diagram is commonly tested • Light overall weightage • Constitute to 3% of marks for past 5 year papers DARRELL ER (COPYRIGHTED) ©

3 MEASURING RATE OF REACTION VOLUME OF GAS COLLECTED CHANGE IN MASS CHANGE IN PRESSURE KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

4 CALCULATING RATE OF REACTION VOLUME OF GAS FORMED The rate of reaction graph measures the volume of gas produced as time passes. As the reaction progresses, the gradient of the graph becomes gentler, showing that the volume of gas produced per unit time is decreasing. This shows that the rate of reaction is falling. At the end of the reaction, the gradient of the graph reaches zero and no more gas is produced. This shows that the reaction is complete and no further reaction is occurring. Set up: DARRELL ER (COPYRIGHTED) ©

5 CALCULATING RATE OF REACTION CHANGE IN MASS As the reaction progresses, reactants are used up and hydrogen gas produced escapes from the flask, the mass of the set-up decreases over time. Comparing the product-time graph observed earlier and this graph, the variation in the gradient of the graphs are similar. The gradient of the graph is the steepest at the start of the reaction and gradually becomes gentler before finally decreasing to zero when the reaction is complete. Set up: DARRELL ER (COPYRIGHTED) ©

6 CONDITIONS FOR SUCCESSFUL REACTION RATE OF REACTION FACTORS - Size of reactant particles - Concentration of reactants - Pressure applied - Temperature of mixture - Use of catalysts KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

7 2 CONDITIONS SUFFICIENT ENERGY RIGHT ORIENTATION 2 CONDITIONS FOR EFFECTIVE COLLISION 1) SUFFICIENT ENERGY 2) RIGHT ORIENTATION Reactions occur when there are effective collisions between reacting particles. In an effective collision, reactants would need to collide with sufficient energy and in the right orientation to form products. Both conditions have to be fulfilled before an effective collision takes place and products can be formed. DARRELL ER (COPYRIGHTED) ©

8 5 FACTORS THAT AFFECT RATE OF REACTION SIZE OF REACTANT PARTICLES CONCENTRATION OF REACTANTS PRESSURE APPLIED TEMPERATURE OF MIXTURE USE OF CATALYSTS DARRELL ER (COPYRIGHTED) ©

9 SIZE OF REACTANT PARTICLES SIZE OF REACTANT PARTICLES The smaller the size of the particles, the faster the rate of reaction. The reason is that having a smaller particle size means that the total surface area for interaction between reacting particles is greater. The frequency of effective collisions in Reaction 1 is higher than 2 because of the greater total surface area that is exposed for interaction between reactants. DARRELL ER (COPYRIGHTED) ©

10 CONCENTRATION OF REACTANTS CONCENTRATION OF REACTANTS A higher concentration means that within the same volume of reactants, there is a higher number of reacting particles. For the reaction with 2 moldm-3, the initial gradient of the graph is steeper compared to the rest, indicating a higher reaction rate. However, the volume of CO2 produced for three reactions are the same. If the number of moles of the limiting reagent used in the reactions is the same, volume of CO2 produced from the reactions will be the same. DARRELL ER (COPYRIGHTED) ©