$$\ce{C2H4(g) + H2(g) ->[platinum] C2H6(g)}$$

$\ce{C2H4(g)}$ is reduced by $\ce{H2(g)}$ in the presence of a solid platinum catalyst, as represented by the equation above. Factors that could affect the rate of the reaction include which of the following?

1. Changes in the partial pressure of $\ce{H2(g)}$
2. Changes in the particle size of the platinum catalyst
3. Changes in the temperature of the reaction system

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All of the factors listed would affect the rate of the reaction.

Changes in the partial pressure of any of the species would result in a change due to Le Chatlier's principle. This is because an increase in the number of reactant gas molecules increases the chance that a collision between reaction molecules occurs.

Similarly, changes in the catalyst size would affect the chance that the reactants have a suitable area to collide and react.

Temperature changes the speed of gas molecules, which also affects the chance that gas molecules collide with the correct amount of energy.