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chemistry igcse acapprinted 136 · PDF 136
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cause the equilibrium to shift to the left and turn darker, while D is incorrect because adding sulfuric acid would
not cause it to shift to the right and turn lighter.
7.Which of the following reactions cannot be reversed?
A. Melting ice
B. Thermal decomposition of hydrated cobalt(II) chloride
C. Combustion of propane
D. Hydration of anhydrous copper(II) sulfate
The answer is C, combustion of propane, since its products, carbon dioxide and water, will not react together to
produce propane once more. A cannot be the answer because water can be frozen to once more provide ice, while
B and D cannot be the answers because both these substances can be hydrated and reduced again to their
anhydrous forms respectively.
8. Reversible reactions occur when products formed in the forward reaction behave as reactants and proceed in
the reverse direction to produce the original reactants again.
Which of the following statements is correct for a reversible reaction?
1 If the forward reaction is exothermic,then the reverse reaction must be endothermic
2 If the forward reaction is endothermic,then the reverse reaction must be exothermic
3 Both directions are exothermic
4 Both directions are endothermic
_____________________________________________________________________________
A. 1 and 2
B. 3 and 4
C. 1 only
D. 3 only
The answer is A, 1 and 2, because in a reversible reaction, one of the two reactions must each be exothermic and
endothermic. B and D cannot be correct because both reactions cannot be of the same type, and C is incorrect
because both the forward and backward reactions can be exothermic or endothermic.
9. Which row correctly describes the conditions used in the Haber process?
temperature/C
pressure/atm
catalyst