This question was not popular among the candidates but the performance was fair.
In (a) (i), some candidates correctly drew and label an energy profile diagram of an endothyrmic reaction indicating the activation energy and heat change, 
H.
However, a few of them wrongly drew the energy profile diagram of an exothermic reaction and hence, lost the marks.
In (a)(ii), candidates correctly explained that addition of a catalyst increase the rate ·of a reaction by providing alternative pathway with lower activation energy and increase in temperature increases the rate of reaction because there will be more effective collisions.
In (b )(i) and (ii), candidates correctly wrote an equation for the thermal decomposition of calcium carbonate (IV) and hence, determined the volume of carbon (IV) oxide produced in the calculation as follows:
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heat |
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(i) |
CaC03(s) |
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CaO(8) + CO2 (g) |
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(ii) |
Molar mass of CaC03 |
= |
40+12+16 x3 = |
100 |
|
10g of CaC03 |
= |
10g = |
0.1 mole |
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|
lOOgmol-1 |
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|
|
1 mole of CaC03 |
= |
1 mole of C02 |
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OR |
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0.1 mole of CaC03 |
= |
0.1 mole of C02 |
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but 1 mole |
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|
= |
22.4dm3 |
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0.1 mole |
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|
= |
2.24dm3 |
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In (c )(i) I - Ill, most candidates correctly gave one use each of coal, wood charcoal and carbon (IV) oxide as follows:
I. Coal - as fuel.
II Wood charcoal - for absorbing poisonous gases/as domestic fuel
Ill. Carbon (IV)oxide - in fire extinguishers.
- manufacture of washing soda by solvay process in . carbonated drinks.
In (c )(ii) I - 11, majority of the candidates correctly wrote the thermal decomposition of NaN03(s) and MgC03(s) as follows:
heat
I. 2NaNo3 
2NaNO3(g) + O2(g)
heat
II. MgCo3(s) 
MgO(s) + CO(g)
In (d)(i)-(v) candidates correctly matches the compounds as follows:
(i) CaCO3 - cement
(ii) Ca(OH)2 - detection of CO2
(iii) CaCO3 - liberates CO2 with addition of acids
(iv) CaO - hygroscopic.
(v) NaOH - deliquescent
