Question

A kettle containing 4 kg of water has just reached its boiling point. How much energy, in joules, is required to boil the kettle dry?

Answer 1

• To calculate the energy required to boil a kettle of water dry, you can use the formula for the heat energy required to change the temperature of a substance:

Q = m * c * ΔT

• Where: Q = heat energy (in joules) m = mass of the substance (in kilograms) c = specific heat capacity of the substance (for water, it's approximately 4.18 J/g°C or 4186 J/kg°C) ΔT = change in temperature (in degrees Celsius)
• In this case, you want to boil the water, which means you need to raise its temperature from its boiling point to its boiling point, so ΔT = 100°C (because water boils at 100°C at standard atmospheric pressure).
• Now, plug in the values:
• m = 4 kg (mass of water) c = 4186 J/kg°C (specific heat capacity of water) ΔT = 100°C
• Q = 4 kg * 4186 J/kg°C * 100°C = 1,674,400 J
• So, it would require approximately 1,674,400 joules of energy to boil 4 kg of water dry in the kettle.