How much is required to heat 2.5 kg water from 20 degrees to a boil?

To heat water from a certain initial temperature t₁ to the boiling point t₂, you need to transfer the amount of heat to it:

Q = s ∙ m ∙ (t₂ – t₁), where m is the mass of water, s is the specific heat capacity of water.

From the reference tables we find the boiling point of water t₂ = 100 ° С and the specific heat of water c = 4200 J / (kg ∙ ° С). It is known that water with a mass of m = 2.5 kg was heated from a temperature of t₁ = 20 ° C to the boiling point. Substitute the values ​​of the quantities into the calculation formula:

Q = 4200 J / (kg ∙ ° С) ∙ 2.5 kg ∙ (100 ° С – 20 ° С);

Q = 840,000 J = 840 kJ.

Answer: to heat water, an amount of heat equal to 840 kJ is required.