# Calorimetry and Change of State

• The specific heat of a substance is the amount of heat energy required to rise the temperature of unit mass of substance through 1k is called specific heat of the substance.
• Among solids liquids gasses specific heat of maximum for Hydrogen gas.
• The amount of heat required to change the state of unit mass of a substance at constant temperature called latent heat.
• Triple point is a point in the phase diagram where a solid liquid and vapour can coexist in equilibrium and at temperature 273.16k and 0.006 atm.
• When two substances at different temperatures are mixed then heat lost by a hot body to heat gained by cold body are equal from principle of methods of mixture.
• The amount of heat required to change the state of H2O from ice to water at 0ºC called latent heat of ice.
• The amount of heat required to change the state of H2O from water to vapour at 100ºC called latent heat of vapourisation.
• Principle of calorimetry represents the law of conservation of heat energy
• Boiling point of water increases with increase of pressure.
• Melting point of ice decrease with increase of pressure.

### Change of State View the Topic in this video From 49:06 To 1:02:01

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1. Calorimetry
Heat lost by hotter body = Heat gained by colder body
m1s1 ΔT = m2s2 ΔT
where, m1 = mass of hot body, m2 = mass of cold body,
s1= specific heat of hot body and
s2= specific heat of cold body

2. The heat required to change the state of a system is proportional to mass of system, Q ∝ m ⇒ Q = mL
where, L is the latent heat.

3. Heat absorbed per unit mass during melting is termed as latent heat of fusion Lf. In case of ice, latent heat of fusion is 80 cal/g.
Q = mLf

4. Heat absorbed per unit mass during vaporisation is termed as latent heat of vaporisation Lv. In case of water, latent heat of vaporisation is 536 cal/g.
Q = MLv