Question

Calculate how much energy is required to heat 20 mL of water from room temperature to 40 C & also how much energy is released when 20 mL of water is cooled from the initial temperature to 10 C

Answer 1

(a) The amount of energy required , Q = mcdt

where

m = mass of water = density x volume of water

                            = 1.0 (g/mL) x 20 mL

                            = 20 g

c = specific heat capacity of water = 4.184 J/g^oC

dt = change in temperature of water = final - initial

    = 40 ^oC - 25 ^oC

    = 15 ^oC

Plug the values we get Q = 20 x 4.184 x 15 J

                                    = 1255.2 J

Therefore the required energy is 1255.2 J

(b) The amount of energy released , Q = mcdt

where

m = mass of water = density x volume of water

                            = 1.0 (g/mL) x 20 mL

                            = 20 g

c = specific heat capacity of water = 4.184 J/g^oC

dt = change in temperature of water

    = 25 ^oC - 10 ^oC

    = 15 ^oC

Plug the values we get Q = 20 x 4.184 x 15 J

                                    = 1255.2 J

Therefore the released energy is also 1255.2 J