Chemical Engineering Basics - Engineering

Q1:

Energy required to compress a hot gas as compared to cold gas will be

A more

B less.

C same.

D more or less depending upon the nature of the gas.

ANS:A - more

The energy required to compress a hot gas compared to a cold gas will generally be more. When compressing a gas, work is done on the gas to reduce its volume, which requires energy input. According to the ideal gas law, PV=nRT, where P is pressure, V is volume, n is the number of moles, R is the gas constant, and T is temperature, it can be observed that for the same volume and number of moles, if the temperature (T) increases, the pressure P) must also increase to maintain the same gas law relationship. Now, during compression, if the gas is initially at a higher temperature (hot gas), it will have higher pressure compared to the same gas at a lower temperature (cold gas), assuming the same initial volume and number of moles. As a result, compressing the hot gas further requires more work done against the higher pressure, thus requiring more energy. Therefore, the energy required to compress a hot gas is generally more than that required to compress a cold gas, assuming all other factors remain constant.