Question

How many KJ are given off when 120 grams of water are cooled from 25°C to -25°C?

Answer 1

-25.116 Kilojoules  are given off when 120 grams of water are cooled from 25°C to -25°C.

Explanation:

GIVEN THAT:

mass of water = 120 grams OR 0.12 Kg

initial temperature = 25 degrees

final temperature = -25degrees

change in temperature (ΔT) = final temperature - initial temperature

                                          -25 -25

                                        = -50 degrees

specific heat capacity of water = 4.186 joule/gram degree Celsius

Q (heat energy transferred) = ?

Formula used,

Q = mcΔT

    Putting the values in equation

Q = 120 X 4.186 X -50

   =  -25116 joules

The energy in joules is converted to kilo joule by dividing it with 1000.

The negative sign in the energy transfer shows that energy is released in the process.