Adding a catalyst increases the rate of a reaction. If the rate increases, then

Question

Adding a catalyst increases the rate of a reaction. If the rate increases, then either k increases, or the order of the reaction changes. Explain which specific trials you might repeat with the catalyst in order to determine which is occurring. In the method of initial rates, only a small amount of reagent is used up (the change in concentration is small compared to the total concentration). The elapsed time is used to calculate the rate. Why is this more accurate than calculating the rate from the amount of time required to use up all of the reagent? If k changes due to the presence of a catalyst (at a constant temperature), what factors in the Arrhenius equation may have changed? Explain which specific trials you might repeat with the catalyst in order to discover which factor has changed.

Explanation / Answer

1. If the rate of reaction increased by adding the catalyst : The rate doubled by doubling the concentration of catalyst, then order of the reaction is constant. If the order is constant, then rate constant increased, this is a zero order reaction.

2. The rate of reaction at smaller concentration and shorter times are more accurate as with higher concentration of substrate the rate of reaction might become independent of concentration.

3. If k changed with temperature, in Arrhenius equation,

k = Ae^(-Ea/RT)

the exponential term has changed

We can run the reaction at different temperatures to confirm this result.

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