What is the change in enthalpy in kJkg of oxygen as its temp

What is the change in enthalpy, in kJ/kg, of oxygen as its temperature changes from 150 to 200 Celsius? Is there any difference if the temperature changes from 0 to 50 Celsius? Does the pressure at the beginning and the end of the process have any effect on the enthalpy change?

Solution

Temperature oC oK Cp kJ/kg/K Cv kJ/kg/K Average CP Average Cv 150 423 0.948 0.678 0.956 0.683 200 473 0.964 0.689 0 273 0.915 0.654 0.919 0.657 50 323 0.923 0.660 The enthalpy change in O2 when heated from 150 to 200C = At Constant volume is 0.683 x50 = 34.16 kJ/kg. the same with constant pressure is 0.956 x 50 = 47.8 kJ/kg The enthalpy change in O2 when heated from 0 to 50C = At Constant volume is 0.657 x50 = 32.84 kJ/kg. the same with constant pressure is 0.919 x 50 = 45.95 kJ/kg The pressure at the beginning and the end of the process has considerable effect because while maitaining the contant pressure , as we increase the heat input to the gas, it needs to expand to maitain constant pressure. This expansion results in addtional work performed by the gas. hence Cp, Specific heat at constant pressure and Cv Specific Heat with constant volume has different values. these two are rlated by Cp/Cv==1.3991 for Oxygen.