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CHEMISTRY, M3 2013 VCE 11*

The following is a student’s summary of catalysts. It contains some correct and incorrect statements.

    1. A catalyst increases the rate of a reaction.
    2. All catalysts are solids.
    3. The mass of a catalyst is the same before and after the reaction.
    4. All catalysts align the reactant particles in an orientation that is favourable for a reaction to occur.
    5. A catalyst lowers the enthalpy change of a reaction, enabling more particles to have sufficient energy to successfully react.
  1. Identify two correct statements.   (1 mark)

  2. Evaluate the student’s summary by identifying two incorrect statements. In each case, explain why it is incorrect.   (4 marks)

Show Answers Only

a.    Statements 1 and 3 are correct.

b.   Answers could include two of the following:

Incorrect statement: All catalysts are solids

→ Catalysts can be solids, liquids, gases or within aqueous solutions.
 

Incorrect statement: All catalysts align the reactant particles in an orientation that is favourable for a reaction to occur.

→ Although solid catalysts orient reactant particles to favor reactions, liquid and gaseous catalysts do not arrange reactants in this manner.
 

Incorrect statement: A catalyst lowers the enthalpy change of a reaction, enabling more particles to have sufficient energy to successfully react.

→ A catalyst does not change the relative energy contents of reactants and products.

→ It does, however, lower the activation energy/increases the proportion of successful collisions/provides an alternative reaction pathway with the same overall \(\Delta H.\)

Show Worked Solution

a.    Statements 1 and 3 are correct.

b.   Answers could include two of the following:

Incorrect statement: All catalysts are solids

→ Catalysts can be solids, liquids, gases or within aqueous solutions.
 

Incorrect statement: All catalysts align the reactant particles in an orientation that is favourable for a reaction to occur.

→ Although solid catalysts orient reactant particles to favor reactions, liquid and gaseous catalysts do not arrange reactants in this manner.
 

Incorrect statement: A catalyst lowers the enthalpy change of a reaction, enabling more particles to have sufficient energy to successfully react.

→ A catalyst does not change the relative energy contents of reactants and products.

→ It does, however, lower the activation energy/increases the proportion of successful collisions/provides an alternative reaction pathway with the same overall \(\Delta H.\)

♦ Mean mark (b) 51%.