#1 rate of reactions_and_collision_theory


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#1 rate of reactions_and_collision_theory

  1. 1. Page 2 - List as many factors as you can that could speed up or slow down a chemical reaction. Below this list take some notes from the video.
  2. 2. What does rate of reaction mean? The speed of different chemical reactions varies hugely. Some reactions are very fast and others are very slow. The speed of a reaction is called the rate of the reaction. What is the rate of these reactions? rusting slow baking fast explosion very fast
  3. 3. Different chemical reactions take place at different speeds. Very fast: • explosion of a petrol-air mixture • precipitation reactions • fireworks going off • coal burning Moderately fast: • reaction of metals or carbonates with dilute acids Slow: • rusting of iron in air • reaction of magnesium with cold water • oil forming • silver tarnishing
  4. 4. Group Thought: Why are some reactions faster than others?
  5. 5. Reactions, particles and collisions Reactions take place when particles collide with a certain amount of energy. The minimum amount of energy needed for the particles to react is called the activation energy, and is different for each reaction. The rate of a reaction depends on two things:  the frequency of collisions between particles  the energy with which particles collide. If particles collide with less energy than the activation energy, they will not react. The particles will just bounce off each other.
  6. 6. Changing the rate of reactions Anything that increases the number of successful collisions between reactant particles will speed up a reaction. What factors affect the rate of reactions?  increased temperature  increased concentration of dissolved reactants, and increased pressure of gaseous reactants  increased surface area of solid reactants  use of a catalyst  use of light for some reactions ie. photography or photosynthesis
  7. 7. Slower and slower! Reactions do not proceed at a steady rate. They start off at a certain speed, then get slower and slower until they stop. As the reaction progresses, the concentration of reactants decreases. This reduces the frequency of collisions between particles and so the reaction slows down. 0% 25% reactants product 50% 75% percentage completion of reaction 100%
  8. 8. GROUP ACTIVITY Reaction was slow at the start and then speeded up Reaction was fast at the start then slowed down. Rate of reaction remained constant throughout the experiment. Volume of gas produced (ml) Time (s) 1. Draw rate graphs for each scenario (use axis given) 2. Which graph would you expect to see for a rates of reaction experiment? 3. How would you calculate the rate of the reaction?
  9. 9. Calculating rate of reaction from graphs How can the rate of reaction be calculated from a graph? 70 hydrogen produced (cm3) 60 x 50 rate of reaction = 40 y x 30 y 20 10 0 0 10 20 time (seconds) 30 40 50 The gradient of the graph is equal to the initial rate of reaction at that time rate of reaction = 45 cm3 20 s rate of reaction = 2.25 cm3/s
  10. 10. Now complete your worksheet! Glue it on page 3 of your notebook (flip page).