Question

How long does it take a 1000W electric kettle to bring 1.0L of water to the boiling point if the initial temperature is 15oc and the kettle is made of 400g of iron? Assume that no heat was lost to the surroundings and that the kettle was 100% efficient?

Answer 1

1 Liter of Water = 1000 grams
ΔT = (100-15)° = 85°
Specific heat capacity of water = 4.184 J/gC°
Specific heat capacity of iron = 0.450 J/gC°

there is an amount of energy required to get 1L of water to 100°C and likewise an energy for the 400g of iron.
energy spent is measured Joules.
Joule = Watt*sec

Joules = (1000W)(T sec) = (4.184 J/gC°)(1000g)(85°) + (0.450 J/gC°)(400g)(85°)

T sec = [ 355640J + 15300J ]/(1000 W)
= 370.94 sec