Question

The heat required to change 1gm ice at 0° to 0°C water is Q₁ and that heat required to convert 1. gm boiling water at 100°C to 100°C steam, is Q₂ then what is true

1. Q₁ > Q₂
2. Q₂ > Q₁
3. Q₁ = Q₂
4. Q₁ = Q₂ = 0

Answer 1

Correct Answer - Option 2 : Q₂ > Q₁

CONCEPT:

• Latent heat is the amount of heat required to change the phase of a unit mass substance into another phase, cal/gm is the unit latent heat
  • Latent heat of fusion is the amount of heat required to change one gram of a solid substance into the liquid
  • Latent heat of vaporization is the amount of heat required to change one gram of liquid into vapor

The ice changes into vapor by absorbing heat at three stages

1. When converted from Solid to liquid
2. While getting heated 
3. During the conversion from liquid to solid

CALCULATION :

Given Lf  = 80 Cal, LV = 536 Cal

Let Q = Heat required to change the state solid to vapor

• The amount of heat required to change the ice into water is given by

⇒ Q1  = m × Lf  = 1 × 80 =  80 cal

• The amount of heat required to change the state from liquid to vapor is given by

⇒ Q^,₂ = m × LV = 1 × 536 = 536 cal,

From the above information, it is clear that  Q₂> Q₁

• Hence, option 2 is the answer