B) 2c2h2(g) + 5o2(g)⟶4co2(g) + 2h2o(l) 6.54 calculate the heats of combustion for the following reactions from the standard enthalpies of formation listed in appendix 2: (a) c2h4(g) + 3o2(g) ⟶2co2(g) + 2h2o(l) (b) 2h2s(g) + 3o2(g) ⟶2h2o(l) + 2so2(g)

a.  ΔH⁸ =  -1420 kJ/mol       b. ΔH⁸ =  -1144.84 kJ/mol

Explanation:

a.

                 C₂H₄ (g) + 3 O₂ (g)  4 CO₂ (g) + 2 H₂O (l)  ΔH⁸ = ?

ΔH⁸f  kJmol  52.47       0                                      -399.5            -285.83

ΔH⁸ = 2(-399.5) + 2 (-285.83) - (52.47)

ΔH⁸ =  -1420 kJ/mol

b.

                       H₂S (g) + 3 O₂ (g) 2 H₂O (l)  + 2 SO₂ (g)

ΔH⁸f  kJmol     -20.50     0                                    -285.83      -296.84

ΔH⁸ =  2(-285.83) + 2 (-296.84) - (-20.50)

ΔH⁸ =  -1144.84 kJ/mol

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.