CAIE IGCSE Chemistry 6.2.7 Catalyst Decreases the Activation Questions

Interpret and draw energy-profile diagrams to show how catalysts lower activation energy while leaving reactant and product energy levels unchanged.

Exam points

state that a catalyst provides an alternative pathway with lower activation energy
draw or interpret a lower catalyst pathway peak while reactant and product energy levels stay unchanged
identify that catalysts increase rate without being used up
explain catalyst effects on activation energy in unfamiliar energy-profile diagrams

[Maximum number: 1]

Hydrogen iodide thermally decomposes into iodine and hydrogen. The reaction is reversible.

\underset{\text { colourless gas }}{2 \mathrm{HI}(\mathrm{~g})} \rightarrow \underset{\substack{\mathrm{I}_{2}(\mathrm{~g}) \\ \text { purple gas }}}{\rightleftharpoons}+\underset{\substack{\mathrm{H}_{2}(\mathrm{~g}) \\ \text { colourless gas }}}{ }

Fig. 4.1 shows a gas syringe containing a mixture of hydrogen iodide, iodine and hydrogen gases. The gas syringe is sealed and the mixture is heated to $300^{\circ} \mathrm{C}$ . The mixture of gases reaches equilibrium and is purple.

Fig. 4.1

Methanol is manufactured by reacting carbon monoxide with hydrogen.

\mathrm{CO}(\mathrm{~g})+2 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{CH}_{3} \mathrm{OH}(\mathrm{~g})

The rate of formation of methanol increases when a catalyst is used.

State the effect that a catalyst has on the activation energy, $E_{\mathrm{a}}$ , of a reaction.

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CAIE IGCSE Chemistry 6.2.7 Catalyst Decreases the Activation Questions question 1