Question

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

1. What is the specific latent heat of the metal?
2. If the specific heat capacity of metal is 200 J kg^-1 K^-1, how much additional heat energy will the metal give out in cooling to -50℃?

Answer 1

1. Mass of metal = 150 g
   Specific latent heat of metal
   L = `"Q"/"m"`
   = `75000 / 150`
   = 500 J g^-1
2. Specific heat capacity of metal is 200 J kg^-1K^-1.
   Change in temperature= 800 − (−50)
   = 850°C (or 850 K).
   ΔQ = mcΔT
   =  0.15 × 200 × 850
   = 25500 J