# How much heat is needed to heat 5kg of water from 20 degrees to boiling and evaporate all the water?

How much heat is needed to heat 5kg of water from 20 degrees to boiling and evaporate all the water? Specific heat capacity of water С = 4200J / kg degrees. The specific heat of vaporization of water r = 2.3 * 10 to the sixth power J / kg.

Given:
m = 5 kilograms is the mass of water;
T1 = 20 degrees Celsius – initial water temperature;
T2 = 100 degrees Celsius – boiling point of water;
c = 4200 J / (kg * C) – specific heat of water;
q = 2.3 * 10 ^ 6 J / kg is the specific heat of vaporization of water.
It is required to determine the amount of heat Q (Joule) required to heat to a boil and evaporate water.
Let’s find the heat that needs to be spent to heat the water to the boiling point:
Q1 = c * m * (T2 – T1) = 4200 * 5 * (100 – 20) = 21000 * 80 = 1680000 Joules.
Let’s find heat to evaporate water:
Q2 = q * m = 2.3 * 10 ^ 6 * 5 = 11,500,000 Joules.
Then the total amount of heat will be equal to:
Q = Q1 + Q2 = 1680000 + 11500000 = 13180000 Joules = 13.2 MJ.
Answer: it is necessary to expend heat equal to 13.2 MJ.

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