Question

An unknown substance has a specific heat of 4.2 kJ/kg °C. How much heat would be needed to change the temperature of 15.0 kg of this substance from 56°C to 14°C? Let (+) indicate that heat is being added to the substance and (-) indicate that heat is being taken from the substance.

Answer 1

Answer : The amount of heat needed to change the temperature of the substance would be, -2646 kJ

Explanation :

Formula used :

`Q=m* c* \Delta T`

or,

`Q=m* c* (T_2-T_1)`

where,

Q = heat needed = ?

m = mass of substance = 15.0 kg

c = specific heat of substance =
`4.2kJ/kg^oC`

`T_1` = initial temperature =
`56^oC`

`T_2` = final temperature =
`14^oC`

Now put all the given value in the above formula, we get:

`Q=15.0kg* 4.2kJ/kg^oC* (14-56)^oC`

`Q=-2646kJ`

Therefore, the amount of heat needed to change the temperature of the substance would be, -2646 kJ