Step 5: Explain the energy change in the reaction. a) Create a new blank document. Type your name at the top.
b) Write a few paragraphs describing the chemical reaction and explaining the energy change in
the reaction. Your document should:
i. identify the reactants and products.
ii. describe the change in energy that occurs as bonds are broken and formed.
iii. identify how the potential energy of the reactants compares to the potential energy of
the products.
iv. state and explain the net change in enthalpy.
v. identify whether the reaction is endothermic or exothermic.
vi. explain how energy is conserved between the reaction and the surrounding
environment.

The reaction: Propane gas plus oxygen gas produces water and carbon dioxide.

(Initial chemical equation: C3H8 + O2 = CO2 + H2O
Balanced chemical equation: C3H8 + 5 O2 = 3 CO2 + 4 H2O)

Table A: Enthalpy of Formation Values for Various Substances

Substance / Hf (kJ/mol)
NH3(g) -46.11
NO2 (g) +33.18
CH4(g) –74.81
C2H4(g) +52.26
C2H6(g) –84.68
C3H8(g) –103.85
C3 H6 (g) +20.42
CO2 (g) –393.51
H2 O(g) –241.82
CH3OH(l) –238.86

Table B: Enthalpy of Formation of Reactants and Products

Substance / Hf (kJ/mol)
C3H8(g) -103.85
O2(g) 0
CO2(g) -393.51
H2O(g) -241.82

Table C: Total Enthalpy of Formation of Reactants and Products

Hf (kJ/mol)
Total enthalpy of reactants -2147.81 kJ/mol - (-103.85kJ/mol)
Total enthalpy of products -2147.81 kJ/mol + 103.85 kJ/mol

Table D: Enthalpy of Reaction

Enthalpy of reaction Hrxn (kJ/mol) -2043.96 kJ/mol
Reaction – endothermic or exothermic: Exothermic