Question

1) 75 g of water at 10 °C is heated by supplying 25200 J of heat energy. Calculate the final temperature of water. [Specific heat capacity of water = 4200 J/kg °C]
2) A solid of specific heat capacity 2.1 J/kg °C at 100 °C is dropped into 400 g of water at 25 °C. If the final temperature is 40 °C, find the mass of the solid.

Answer 1

Heat absorbed = ΔH = m s ΔT
     25, 200 J = (75/1000) kg * 4, 200 J/kg/⁰C  * ΔT
   =>  ΔT =  80 ⁰C
So final temperature is : 10⁰C + 80⁰C = 90 ⁰C

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 mass of solid = m kg
   Heat energy given out by stone  =  heat absorbed by water
   m * 2.1 J/kg/⁰C * (100 ⁰C - 40 ⁰C)  =  0.4 kg * 1000 J/kg/⁰C * (40 ⁰C - 25⁰C)
       m = 400 * 15 / (2.1 * 60)  =  47.619 kg

If the specific heat capacity of the stone is 2.1 kJ/kg/⁰C then the mass of the solid  is :  47.619 grams