Phase Changes & Latent Heat — Homi Bhabha Class 9 Chemistry MCQs with Solutions
Free Homi Bhabha Class 9 Chemistry Phase Changes & Latent Heat MCQs with step-by-step solutions (10 questions). Part of Matter & Its States. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Phase Changes & Latent Heat · medium · theory
The direct change of a solid into a gas without passing through the liquid state is called:
A. freezing
B. sublimation ✓ Correct
C. condensation
D. melting
Solution: Sublimation is the solid-to-gas transition (e.g. camphor, dry ice).
Q2 — Phase Changes & Latent Heat · medium · theory
Which of the following substances undergoes sublimation?
A. Camphor ✓ Correct
B. Sugar
C. Common salt
D. Iron
Solution: Camphor (like naphthalene and dry ice) sublimes directly from solid to vapour.
Q3 — Phase Changes & Latent Heat · hard · theory
The heat energy absorbed by a solid at its melting point to change into a liquid, without any rise in temperature, is called the:
A. latent heat of vaporisation
B. latent heat of fusion ✓ Correct
C. specific heat
D. heat of combustion
Solution: Latent heat of fusion is absorbed at constant temperature to convert solid to liquid.
Q4 — Phase Changes & Latent Heat · hard · theory
Evaporation of sweat cools our body because evaporation:
A. absorbs latent heat from the body ✓ Correct
B. produces a new substance
C. releases heat to the body
D. raises body temperature
Solution: Evaporating sweat takes latent heat of vaporisation from the skin, producing a cooling effect.
Q5 — Phase Changes & Latent Heat · medium · theory
During the melting of ice, the temperature of the ice–water mixture remains at 0 °C because the heat supplied is used to:
A. freeze the water again
B. raise the temperature quickly
C. produce a gas
D. overcome the forces holding the solid particles together (latent heat) ✓ Correct
Solution: The absorbed latent heat breaks the bonds of the solid rather than raising the temperature.
Q6 — Phase Changes & Latent Heat · hard · numerical
The heat required to melt 2 kg of ice at 0 °C (latent heat of fusion of ice = 336000 J/kg) is:
A. 674 J
B. 672000 J ✓ Correct
C. 168000 J
D. 336000 J
Solution: Heat $Q = mL = 2 \times 336000 = 672000$ J.
Q7 — Phase Changes & Latent Heat · easy · theory
The change of a solid directly into vapour without first becoming a liquid is called
A. fusion
B. sublimation ✓ Correct
C. freezing
D. condensation
Solution: Sublimation is the direct solid-to-gas change, seen in substances such as camphor, naphthalene and dry ice.
Q8 — Phase Changes & Latent Heat · medium · theory
While ice is melting, its temperature stays at 0 degrees C even though heat is continuously supplied. This supplied heat is used mainly to
A. raise the temperature of the ice above 0 degrees C
B. increase the total mass of the water formed
C. overcome the forces holding the particles together (latent heat of fusion) ✓ Correct
D. create new water particles from the heat
Solution: During melting the absorbed heat (latent heat of fusion) is spent breaking the bonds between the particles rather than raising temperature, so the temperature stays constant until all the ice has melted.
Q9 — Phase Changes & Latent Heat · hard · numerical
How much heat is required to completely melt 200 g of ice at 0 degrees C into water at 0 degrees C? (Latent heat of fusion of ice = 336 J/g)
A. 1680 J
B. 336 J
C. 6720 J
D. 67200 J ✓ Correct
Solution: Heat = mass x latent heat of fusion = 200 g x 336 J/g = 67200 J.
Q10 — Phase Changes & Latent Heat · hard · numerical
The latent heat of vaporisation of water is 2260 J/g and the latent heat of fusion of ice is 336 J/g. The heat needed to turn 50 g of water at 100 degrees C into steam at 100 degrees C is about how many times the heat needed to melt 50 g of ice at 0 degrees C?
A. about 5 times
B. about 3 times
C. about 7 times ✓ Correct
D. about 11 times
Solution: Vaporisation heat = 50 x 2260 = 113000 J; fusion heat = 50 x 336 = 16800 J. The ratio 113000 / 16800 is about 6.7, which rounds to roughly 7 times.