Question

If 8 kg of air at 27°C are heated at constant pressure until the absolute temperature doubles, calculate the heat required in kJ.    

Answer 1

In absolute (Kelvin) scale, 27^oC = 27 + 273 = 300 K.

Therefore, doubling the temperature means increasing it by another 300 K ($\Delta{T}=300K$ ).

The specific heat capacity of air at constant pressure (c_p) at 300 K is approximately 1.01 $\frac{kJ}{kg\cdot{K}}$ .

Now the heat can be calculated:

$Q=c_pm\Delta{T}=1.01\frac{kJ}{kg\cdot{K}}\times8kg\times300K=2424kJ$

Answer: 2424 kJ