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TOPIC 5. RATE OF REACTION-ACTIVITIES

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TOPIC 5. RATE OF REACTION-ACTIVITIES

1. 1. TOPIC 5 RATE OF REACTION ACTIVITIES The rate of a reaction is the speed at which a reaction happens. If a reaction has a slow reaction rate, that means the molecules combine at a slower speed than a reaction with a fast reaction rate. Some reactions take hundreds, maybe even thousands of years while others can happen in less than one second. The rate of reaction depends on the type of molecules that are combining. Collision theory states that the more collisions in a system, the more probable combinations of molecules will happen. As the number of collisions in a system increases, more combinations of molecules will occur. The reaction will go faster, and the rate of that reaction increases. Reactions happen, no matter what. Chemicals are always combining or breaking down. The reactions happen over and over but not always at the same speed. A few things affect the overall speed of the reaction and the number of collisions that can occur. Concentration: If there is more of a substance in a system, there is a greater chance that molecules will collide and speed up the rate of the reaction. If there is less of something, there will be fewer collisions and the reaction will probably happen at a slower speed. Temperature: When you increase the temperature of a system, the molecules bounce around a lot more (because they have more energy). When they move faster, they are more likely to collide. That fact means they are also more likely to combine. When you decrease the temperature, the molecules are slower and collide less. That temperature drop slows down the rate of the reaction. Pressure: Pressure affects the rate of reaction, especially when you study gases. When you increase the pressure, the molecules have less space in which they can move. That greater concentration of molecules increases the number of collisions. When you decrease the pressure, molecules don’t collide as often. The lower pressure decreases the rate of reaction. Particle size: Reactions in which one of the reactants is a solid can be speeded up or slowed down by altering the particle size of the solid. The surface area of the solid will affect how fast the reaction goes. So the larger the surface area of the solid, the faster the reaction will be. Catalyst: The presence of a catalyst increases the reaction rate (in both the forward and reverse reactions) by providing an alternative pathway with lower activation energy.
2. 2. 1. Work in groups of 3. Work out the correct order for the 6 slips of the text and stand in that order. The teacher is going to ask you to read your slips in your chosen order to check that they are correct. The whole class listens and checks. 1. The rate of a reaction is the speed at which a reaction happens. If a reaction has a slow reaction rate, that means the molecules combine at a slower speed than a reaction with a fast reaction rate. Some reactions take hundreds; maybe even thousands of years while other can happen in less than one second. The rate of reaction depends on the type of molecules that are combining. Collision theory states that the more collisions in a system, the more probable combinations of molecules will happen. As the number of collisions in a system increases, more combinations of molecules will occur. The reaction will go faster, and the rate of that reaction increases. Reactions happen, no matter what. Chemicals are always combining or breaking down. The reactions happen over and over but not always at the same speed. A few things affect the overall speed of the reaction and the number of collisions that can occur. Concentration: If there is more of a substance in a system, there is a greater chance that molecules will collide and speed up the rate of the reaction. If there is less of something, there will be fewer collisions and the reaction will
3. 3. probably happen at a slower speed. Temperature: When you increase the temperature of a system, the molecules bounce around a lot more (because they have more energy). When they bounce around more, they are more likely to collide. That fact means they are also more likely to combine. When you decrease the temperature, the molecules are slower and collide less. That temperature drop slows down the rate of the reaction. Pressure: Pressure affects the rate of reaction, especially when you study gases. When you increase the pressure, the molecules have less space in which they can move. That greater concentration of molecules increases the number of collisions. When you decrease the pressure, molecules don't collide as often. The lower pressure decreases the rate of reaction. Particle size: Reactions in which one of the reactants is a solid can be speeded up or slowed down by altering the particle size of the solid. The surface area of the solid the solid will affect how fast the reaction goes. So the larger the surface area of the solid, the faster the reaction will be. Catalyst: The presence of a catalyst increases the reaction rate (in both the forward and reverse reactions) by providing an alternative pathway with lower activation energy
4. 4. 2. Complete the sentences with the appropriate words listed below. Remember that you may have to use the words more than once: a. If there is an ………………….in the number of collisions in a system,………… combinations of molecules will occur. b. If there is a …………….in the number of collisions in a system,....................... combinations of molecules will occur. c. If we increase the concentration of substances there is a ………… chance that molecules will collide and ………………….the rate of the reaction. d. If we decrease the concentration of substances, the rate of the reaction…………………………………………… e. When you raise the temperature of a system there is a ……...............chance that molecules will collide and …………………………...the rate of the reaction. f. When you lower the temperature the molecules move more slowly, collide less and the rate of the reaction …………………………. g. An increase in pressure…………………………. the rate of reaction h. A decrease in pressure …………………………the rate of reaction i. The …………… the surface area of the solid, the ………… the reaction will be. j. The……………..the surface area of the solid, the……………the reaction will be. j. The presence of a catalyst ……………………………. the reaction rate
5. 5. 3. In Summary: SLOW REACTIONS FAST REACTIONS Large particles …………………………………… ……………………………. High concentration Low temperatures …………………………………… ……………………………….. High pressure