Question

A molten metal of mass 150 g is kept at its melting point ${800}^{o}C$. When it is allowed to freeze at the same temperature, it gives out 75,000 J of heat energy.

(a) What is the specific latent heat of the metal ?

(b) If the specific heat capacity of metal is $200Jk{g}^{-1}{K}^{-1}$, how much additional heat energy will the metal give out in cooling to $-{50}^{o}C$ ?

Answer 1

(a) $mL=H\Rightarrow 150L=75000\Rightarrow L=500J/g$

(b) m = 150 g = 0.15 kg

S = 200 J/kg

Δt = t1 - t2 = (800 - (-50)) = (800 + 50) = ${850}^{o}C$
We know that,
Q = m c Δt
= 0.15 $\times$ 200 $\times$ 850
= 25500 J