BPSC CCE Prelims
Chemical Reactions Previous Year Questions (PYQs)
Practice solved questions for Chemical Reactions with detailed step-by-step solutions, key insights, and trend analysis for BPSC CCE PRELIMS.
Solved Previous Year Questions
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Which of the following are exothermic processes?
i. Evaporation of water.
ii. Dilution of an acid (H2SO4).
iii. Reaction of water with quick lime.
iv. Sublimation of camphor (crystals).
Detailed Explanation:
Exothermic processes release heat to surroundings; endothermic processes absorb heat.
i. Evaporation of water – absorbs heat from surroundings (endothermic).
ii. Dilution of H₂SO₄ – releases large amount of heat when water is added (exothermic).
iii. Reaction of water with quick lime (CaO) – forms slaked lime with vigorous heat release (exothermic).
iv. Sublimation of camphor – solid to gas transition requires heat absorption (endothermic).
Only ii and iii are exothermic.
What happens to the weight of iron, when it rusts?
Detailed Explanation:
Rusting is oxidation of iron (4Fe + 3O₂ → 2Fe₂O₃·xH₂O), where oxygen and water molecules bond to iron atoms, increasing total mass as hydrated iron oxide forms.
Over time, the rust layer flakes off or detaches from the surface due to its brittle nature, causing the overall weight to decrease.
Therefore, the weight first increases (oxidation) then decreases (flaking), making Option 2 the correct answer.
Consider the following statements :
- Addition of salt to pure water increases the boiling point of water and decreases the freezing point of water.
- When methyl alcohol is added to water boiling point of water decreases.
Which of the above statements is/are correct?
Detailed Explanation:
Salt (NaCl) is a non-volatile solute that causes boiling point elevation and freezing point depression through colligative properties—saltwater boils at a higher temperature and freezes at a lower temperature than pure water.
Methyl alcohol (methanol) is a volatile solute with higher vapor pressure than water. When added to water, it increases the overall vapor pressure of the mixture, causing the boiling point to decrease.
Therefore, both statements correctly describe opposite effects due to different solute types, making Option 3 the correct answer.
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