Specific Heat Capacity and Latent Heat Questions - GCSE standard

Q6. The photo shows a coffee machine. The coffee machine uses an electric element to heat water.

The coffee machine heats water from 20 °C to 90 °C.

The power output of the coffee machine is 2.53 kW.

Given that the specific heat capacity of water is 4200 J/kg °C, calculate the mass of water that the coffee machine can heat in 14 seconds.

This requires you to use the specific heat capacity equation - E = mcΔθ

On the right hand side of your page set out what you have been given and change it into the correct unit to use the equation.

E = ?

Δθ = 90 - 20 = 70 °C

m = ? kg

c = 4200 J/kg °C

So, we have two unknowns - the mass and the energy given to the water. We have to use the power value and the time to find the energy:

2.53 kW = 2.53 x 10³J/s

so, in 14 seconds the element provides 2.53 x 10³ x 14 J of energy

E = 35.42 x 10³ J

E = 35.4 x 10³ J

Now we are in business! We have one unknown and can work that out....

E = mcΔθ

m = E/(cΔθ)

m = 35.42 x 10³/(4200 x 70)

m = 0.12kg

(Total 6 marks)