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Rates of Reaction: Question 5

Syllabus 6.2

Multiple choice Extended 1 mark

A margarine manufacturer hardens liquid vegetable oil into a solid fat by reacting it with hydrogen gas, using a nickel catalyst: vegetable oil(l)+H2(g)→Ni catalystmargarine(s)\text{vegetable oil}(l) + \text{H}_2(g) \xrightarrow{\text{Ni catalyst}} \text{margarine}(s)

This is an exothermic reaction: the reactants have more energy than the products.

Which statement correctly describes the effect of the nickel catalyst on this reaction?

Choose an answer to check it, then compare with the worked solution below.
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Worked solution

Step 1: Recall what a catalyst does and does not change

A catalyst speeds up a reaction by offering an alternative reaction pathway with a lower activation energy, EaE_a. It does not change:

  • the kinetic energy of the particles (that is the effect of temperature),
  • how often particles collide (that is the effect of concentration or pressure),
  • or the overall energy change of the reaction (the difference in energy between reactants and products stays fixed, since the identities of reactants and products are unchanged).

Step 2: Check each option

  • Option A is wrong: it describes the effect of raising the temperature, not the effect of a catalyst. A catalyst does not make particles move faster.
  • Option B correctly describes a catalyst: it lowers the activation energy needed, so a greater proportion of the collisions between vegetable oil and hydrogen particles now have enough energy to react successfully.
  • Option C is wrong: although the first part (lowering activation energy) is correct, a catalyst does not change how much energy the reaction releases overall. The energy of the products relative to the reactants is fixed by their chemical identities, not by the presence of a catalyst.
  • Option D is wrong: it describes the effect of increasing concentration or pressure (more frequent collisions), not the effect of a catalyst. The activation energy is exactly what a catalyst does change.

Step 3: Select the answer

Only option B correctly links the catalyst to a lower activation energy and a greater proportion of successful collisions, without wrongly claiming any change to particle energy, collision frequency, or the reaction’s overall energy change.

Final answers

  • option B\boxed{\text{option B}}, the nickel catalyst provides a pathway with lower activation energy, so more collisions succeed, without changing the enthalpy change of the reaction.