Question

CaO(s) + H2O(l) - Ca(OH)2(s)

enthalpy of rxn= -63.7 kJ/molrxn

Calcium oxide, CaO(s), has been proposed as a substance that can be used to heat water quickly for portable heating packs or for cooking. When placed in water, Cao(s) reacts as shown by the equation above.

A student wants to design a heating pad that could heat a 150.0 g sample of water from 25.0°C to 60.0°C.

Calculate the amount of heat, in joules, that the water must absorb for its
temperature to change by this amount. (Assume that the specific heat capacity
of the water is 4.18 J/gK).

Answer 1

21,976 J

Step-by-step explanation:

In order to increase the temperature of a certain amount of a substance by
`\Delta T`, the amount of heat that must be supplied to the substance must be:

`Q=mC\Delta T`

where

m is the mass of the substance

C is the specific heat capacity of the substance

`\Delta T` is the increase in temperature

For the sample of water in this problem we have:

`m=150.0 g` is the mass

`C=4.186 J/g^(\circ)C` is the specific heat capacity of water

`\Delta T=60.0-25.0=35.0^(\circ)C` is the increase in temperature

Therefore, the amount of heat that must be supplied is

`Q=(150.0)(4.186)(60-0-25.0)=21,976 J`