83) Liquid fuels have higher calorific value than solid fuels.

84) The free expansion process is __________ non-flow process.

85) A mixture of gas expands from 0.03 m³ to 0.06 m³ at a constant pressure of 1 MPa and absorbs 84 kJ of heat during the process. The change in internal energy of the mixture is

86) The gas constant (R) is equal to the __________ of two specific heats.

87) Hydrogen is the __________ substance.