Calculate the Δ H ∘ reaction for C 3 H 8 ( g ) 5 O 2 ( g ) ⟶ 3 CO 2 ( g ) 4 H 2 O ( l ) given Δ H ∘ f ( C 3 H 8 ) = − 103.85 kJ/mol Δ H ∘ f ( CO 2 ) = − 393.5 kJ/mol Δ H ∘ f ( H 2 O ) = − 285.83 kJ/mol .