Propane: determine the heating value (kJ/kg or Btu/pound or Btu/gallon) of the fuel in the propane tank you bought for your back-yard grill. Then determine the chemical energy content (kJ or Btu) of the fuel in the tank?
Coal: what is heating value of coal? This is normally expressed as BTU per short ton, or as kJ per tonne. Do you think this would vary a lot with the source and type of the coal (ie, the location of the coal mine)?
A steam-cycle power plant and a gas turbine engine have identical efficiencies when separately operated: 33%. However, when combined, the waste heat of the gas turbine engine serves as the heat source for the steam-cycle power plant. What is the value of the efficiency of this combined cycle? Note: the only source of fuel input is the gas turbine engine. Each engine has work output. Thus the efficiency equation for the combined cycle is: h = (WGT + WST)/QH-GT.