The average propane cylinder for a residential grill holds approximately 18 kg of propane. how much energy (in kj) is released by the combustion of 20.00 kilograms of propane in sufficient oxygen?

In order to answer this, we mus know the data for the heat of combustion of propane. This is an empirical data that you can search online. The heat of combustion is -2220 kJ/mol. The molar mass of propane of 44.1 g/mol. The solution is as follows:

ΔH = -2220 kJ/mol (1 mol/44.1 g)(1000g/1kg)(20 kg)
ΔH = -1006802.721 kJ or -1 GJ

30litre of li2o is 1.0002mole approximately 1 mole