1.4 Short Notes: Collision Theory Part 2

  1. Five (5) factors that will increase rates of reaction:
    1. Surface area of solid reactants
    2. Higher concentration
    3. Higher temperature
    4. Higher pressure
    5. Presence of a catalyst
  2. Effect of surface area on rate of reaction - (↑ surface area of reactants = ↑ rate of reaction)
    Example: Compare the rate of reaction between 1g of Magnesium ribbon and 1g of Magnesium powder in 0.1 mol dm-3 of H2SO4 solution.
    1. The Magnesium ribbon takes 30 seconds to dissolve while the Magnesium powder takes 15 seconds to dissolve because the ribbon has a smaller surface area exposed to the ions from the acid compared to the powder.
    2. The frequency of effective collisions (successful collisions) is higher where the surface area is higher.
  3. Effect of temperature in rate of reaction.
    Example: 1g of Magnesium ribbon in different temperatures of H2SO4 aqueous solution, 25oC and 40oC.
    1. H2SO4 + Mg → MgSO4 + H2
    2. For example, in 25oC, the experiment takes 30 seconds to complete while, in 40oC the experiment takes 15 seconds to complete.
    3. At low temperature, the kinetic energy of the particles is low and the move relatively slow.
    4. Some particles collide with each other with insufficient energy, and they just bounce off without any reaction occurring. This is known as inefficient reaction.
    5. Hence, the rate of reaction is low at low temperature

Questions

  1. What is a catalyst?
  2. Give 3 examples of important catalyst in the industry.
  3. What is the function of catalyst?

Answers:

  1. A catalyst is a chemical that increases the rate of reaction by reducing the activation energy required for a reaction. A catalyst does not change chemically during a reaction and can be reused many times.
  2. Nickel catalyses the hydrogenation of unsaturated fats to margarine. Iron catalyses the combination of unreactive nitrogen and hydrogen to form ammonia in Haber Process. Vanadium (V) oxide is used in the Contact Process.
  3. To increase the rate of reaction.

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