# The standard enthalpies of formation of gaseous propyne, propylene, and propane are +185.4, +20.4, and -103.6 KJ/mol, respectively.Calculate the heat evolved per mole on combustion of each substance to yield CO2 and water.Calculate the heat evolved on combustion of 1 kg of each substance.Which is the most efficient fuel in terms of heat evolved per unit mass?

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• The standard enthalpies of formation of gaseous propyne, propylene, and propane are +185.4, +20.4, and -103.6 KJ/mol, respectively.
1. Calculate the heat evolved per mole on combustion of each substance to yield CO2 and water.
2. Calculate the heat evolved on combustion of 1 kg of each substance.
3. Which is the most efficient fuel in terms of heat evolved per unit mass?
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Step 1

Combustion reaction of propyne is given below.

C3H4 + 4 O2 ---> 3 CO2 + 2 H2O

Combustion reaction of propylene is given below.

C3H6 + 9/2 O2 ---> 3 CO2 + 3 H2O

Combustion reaction of propane is given below.

C3H8 + 5 O2 ---> 3 CO2 + 4 H2O

Enthalpy of formation of H2O (l) = -241.818 kJ/mol

Enthalpy of formation of CO2 (g) = -393.509 kJ/mol

Enthalpy of formation of O2 (g) = 0 kJ/mol

Enthalpy of formation of propyne = 185.4 kJ/mol

Enthalpy of formation of propylene = 20.4 kJ/mol

Enthalpy of formation of propane = -103.6 kJ/mol

Enthalpy of reaction can be calculated as follows,

Step 2
1. Enthalpy of combustion for propyne, propylene and pr...

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