CatalystsAQA GCSE Chemistry: Flashcards

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How is mean rate of reaction calculated?

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How is mean rate of reaction calculated?: Mean rate = quantity of reactant used (or product formed) ÷ time taken
How do you find the rate of reaction at a specific moment from a graph?: Draw a tangent to the curve at that point and calculate its gradient
List the five factors that affect the rate of a chemical reaction.: Concentration, pressure (of gases), surface area (of solids), temperature, and the presence of a catalyst
According to collision theory, why does increasing concentration speed up a reaction?: It increases the frequency of collisions between reacting particles
Why does increasing temperature have a bigger effect on rate than increasing concentration?: It increases both the frequency and the energy of collisions, not just the frequency
What is a catalyst?: A substance that changes (speeds up) the rate of a reaction without being used up itself
How does a catalyst increase reaction rate?: By providing an alternative reaction pathway with a lower activation energy
What are enzymes?: Biological catalysts that speed up reactions in living organisms
How can you identify a catalyst from a chemical equation?: It does not appear in the balanced equation, since it isn't consumed in the reaction
Does a catalyst change the overall energy released or absorbed by a reaction?: No — it only lowers the activation energy needed, not the overall energy change
What happens to a catalyst's mass and identity at the end of a reaction?: They are unchanged
Why might a slope on a rate-vs-time graph flatten out?: Because a reactant is being used up, slowing then stopping the reaction