Chemistry 0620 · IGCSE · Rate of reaction

Rate of reaction — practice question

An enzyme speeds up the decomposition of aqueous hydrogen peroxide, H$_2$O$_2$. 2H$_2$O$_2$ $ ightarrow$ 2H$_2$O + O$_2$ The oxygen released as the reaction continues is measured to determine the rate. The graph shows the results.
(a(i))[1]

Deduce the volume of oxygen gas evolved when the reaction has finished.

(a(ii))[1]

Deduce the volume of oxygen gas obtained after 50 seconds from the start of the reaction.

(b)[2]

Draw a line on the grid to show how the oxygen volume varies with time when hydrogen peroxide of a higher concentration is used.

(c)[2]

Describe how each of the following affects the rate at which hydrogen peroxide decomposes: • The reaction is carried out at a lower temperature, with all other conditions unchanged. • The reaction is carried out without an enzyme, with all other conditions unchanged.

(d(i))[1]

Put the three oxides in order of how well they catalyse the reaction. Put the best catalyst first.

(d(ii))[1]

Describe how the rate of decomposition of hydrogen peroxide changes when large pieces of catalyst are used rather than powdered catalyst. Every other condition stays the same.

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