Determine the change in thermal energy of 100 g of copper (m = 63,5, debye 348k) if it is cooled from

(a) 300 k to 4 k,

(b) 78 k to 4 k

(c) 20 k to 4 k.

if the latent heat of liquid he is 2700 j. l -1 , calculate how much he is needed to bring the cooling about in each case.

given,

mass of copper = 100 g

latent heat of liquid (He) = 2700 J/l

a) change in energy

Q = m Cp (T₂ - T₁)

Q = 0.1 × 376.812 × (300 - 4)

Q = 11153.63 J

He required

Q = m L

11153.63 = m × 2700

m = 4.13 kg

b) Q = m Cp (T₂ - T₁)

Q = 0.1 × 376.812 × (78 - 4)

Q = 2788.41 J

He required

Q = m L

2788.41 = m × 2700

m = 1.033 kg

c) Q = m Cp (T₂ - T₁)

Q = 0.1 × 376.812 × (20 - 4)

Q = 602.90 J

He required

Q = m L

602.9 = m × 2700

m =0.23 kg

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explanation: