8.24 Find the missing properties of T, P, s, and x for water at a. P = 25 kPa, s = 7.7 kJ/kg K b. P = 10 MPa, u = 3400 kJ/kg c. T = 150◦C, s = 7.4 kJ/kg K

1. Calculate the quantity of heat energy which must be transferred to 2.25 kg of brass to 
raise its temperature from 20 ℃ to 240 ℃ if the specific heat of brass is 394 J.kg-K.

2. Find the change in temperature produced by 10 kJ of heat energy added to 500 g 
copper. Specific heat of copper 0.39 kJ/kg-K.

3. Explain why, for a gas, the specific heat at constant volume has a different value 
from the specific heat at constant pressure.
An ideal gas is contained in a cylinder fitted with a piston. Initially the temperature of the 
gas is 15℃. If the mass of the gas is 0.035 kg, calculate the quantity of heat energy 
required to raise the temperature of the gas to 150 ℃ when:
(a) The piston is fixed;
(b) The piston moves and the pressure is constant.
For the gas, 𝑐𝑣 = 676 J/kg-K and 𝑐𝑝 = 925 J/kg-K.