An open beaker of water in equilibrium with water vapour is in a sealed container. When a few grams of glucose are…
Chemical Equilibrium · Class 11 · JEE Main Previous Year Question
An open beaker of water in equilibrium with water vapour is in a sealed container. When a few grams of glucose are added to the beaker of water, the rate at which water molecules:
- a
Leaves the vapour increases
- b
Leaves the solution increases
- c✓
Leaves the solution decreases
- d
Leaves the vapour decreases
Leaves the solution decreases
Step 1 — Effect of glucose on water: Glucose is a non-volatile solute. When added to water:
- It lowers the vapour pressure of water (Raoult's law)
- The mole fraction of water decreases
Step 2 — Effect on rates:
- Rate of evaporation (water leaving solution) ∝ vapour pressure of solution decreases ✓
- Rate of condensation (water leaving vapour) depends on vapour pressure of water in gas phase initially unchanged
Step 3 — New equilibrium: Since rate of evaporation < rate of condensation, net condensation occurs until a new (lower) vapour pressure equilibrium is established.
Answer: Option (3) — Leaves the solution decreases
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