States of matter

Solution:

Substances can exist in three states (phases) – solid, liquid, and gas.
Melting – change from solid to liquid
Freezing – change from liquid to solid
Evaporation – change from liquid to gas
Boiling – evaporation occurring when the vapor pressure equals the external pressure
Condensation – change from gas to liquid
Sublimation – direct change from solid to gas

                   
L = latent heat (melting, freezing, evaporation, boiling ...)
l = specific latent heat (melting, freezing, evaporation, boiling ...)
m = mass of substance
                   
For ice – water – steam applies:
t _melt = t _freeze = 0⁰C,      t _boil = t _condense = 100⁰C,    

l _melt = l _freeze = 334.10³J.kg^-1,    l _boil = l _condense = 2260.10³J.kg^-1

l _evap(20⁰C) = 2430.10³J.kg^-1,  l _sub = 2830.10³J.kg^-1

c(H₂O) = 4180 J.kg^-1.K^-1,   c(ice) = 2100 J.kg^-1.K^-1

Conversion of ice to steam:    Q = Q₁ + L₁ +Q₂ + L₂ + Q₃
Q₁ = heat needed to warm ice to melting point
L₁ = heat needed to convert ice to water
Q₂ = heat needed to warm water to boiling point
L₂ = heat needed to convert water to steam
Q₃ = heat needed to warm steam

Solution:

Analysis:

m = 10 kg,  t₁ = 20⁰C,  t_m (Al) = 660⁰C,  c(Al) = 896 J.kg^-1.K^-1
l_m (Al) = 400.10³J.kg^-1

To melt the aluminum object, approximately 9.73 MJ of heat is required.

Solution:

Analysis:

m = 5 kg,  L = 1.02.10⁶J,

The specific latent heat of fusion of copper is l_m (Cu) = 204,000 J.kg^-1

Solution:

Analysis:

m₁ = 5 l = 5 kg,  t₁ = 50⁰C,  Δ t = 50⁰C,  c1(H₂O) = 4180 J.kg^-1.K^-1
l_m (ice) = 334,000 J.kg^-1

The mass of ice must be m = 3.13 kg.

Solution:

Analysis:

m = 10 kg,  Δt = 100⁰C = 100 K,  c₁ = 4180 J.kg^-1.K^-1,
l_v = 2.26.10⁶ J.kg^-1