Calculating Heat energy

Question

A 12w electric heater, working at its stated power,is found to heat 0.02kg of water from 15 to 30 degrees celcius in 2 minutes.

a) Calculate the heat energy produced by the heater in 2 minutes

 

 

b)Calculate the heat energy absorbed by the water in 2 minutes

 

c)Account for the difference in a) and b)

Answer 1

See solution posted at

https://www.wyzant.com/resources/answers/296849/calculating_heat_energy

 

Answer 2

(a)

 

c = specific heat of water = 4180 J/(kg°C)

 

Q₁ = mcΔT = (0.02 kg) [4180 J/(kg°C)] (30 - 15)°C = 1254 J

 

(b)

 

Q₂ = Pt = (12 W)(120 s) = 1440 J

 

(c)

 

Q₁ < Q₂ because not all the heat produced by the heater is absorbed by the water.  There is an inefficiency to the heating system, even when running on stated power.  Some of the heat escapes into the environment without being used to raise the temperature of the water.