CAIE IGCSE Chemistry 5.1.6 And Label Reaction Pathway Diagrams Questions

Draw energy profiles with reactants, products, activation energy and overall enthalpy change labelled.

Exam points

draw and label energy level diagrams
place reactants and products for exothermic reactions
show activation energy and overall enthalpy change
label ΔH and activation-energy arrows correctly
complete reaction pathway diagrams from equations
represent energy profiles for unfamiliar reactions

[Maximum number: 3]

Chemical reactions can involve transfer of thermal energy.

Tetrachloromethane gas, $\mathrm{CCl}_{4}(\mathrm{~g})$ , reacts with steam as shown.

\mathrm{CCl}_{4}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{HCl}(\mathrm{~g})

The reaction is reversible. The forward reaction is exothermic.

Fig. 5.1 shows an incomplete reaction pathway diagram for the forward reaction.

\mathrm{CCl}_{4}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightleftharpoons \mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{HCl}(\mathrm{~g})

Fig. 5.1

On Fig. 5.1:
- insert the formulae of the reactants and products
- draw an arrow, labelled $E_{\mathrm{a}}$ , to show the activation energy
- draw an arrow, labelled $\Delta H$ , to show the transfer of energy in the reaction.

M1 Labels mark

$\mathrm{CCl}_{4}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g})$ on reactant line

AND

$\mathrm{CO}_{2}(\mathrm{~g})+4 \mathrm{HCl}(\mathrm{g})$ on product line

M2 Activation E mark

upward arrow labelled $E_{\mathrm{a}}$ from energy level of reactants to top of 'hump'

M3 Energy change mark

one downward arrow labelled $\Delta \mathrm{H}$

AND

energy change starting from E level of reactants and finishing at E level of products

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CAIE IGCSE Chemistry 5.1.6 And Label Reaction Pathway Diagrams Questions question 1