Question

Calculate ΔH of xn for the following reaction, after it is properly balanced with smallest whole-number coefficients: C₂H₆(g) + O₂(g)
`\longrightarrow` CO₂(g) + H₂O(g)[unbalanced]ΔH of [C₂H₆(g)] = −84.667 kJ/mol ΔH of [CO₂(g)] = −393.5 kJ/mol ΔH of [CO₂(aq)] = −412.9 kJ/mol ΔH of [H₂O(g)] = −241.826 kJ/mol ΔH of [H₂O(l)] = −285.840 kJ/mol

Answer 1

ΔH rx = -2855,622 KJ (assuming standard conditions of temperature and pressure for the reaction)

Step-by-step explanation:

First we need to balance the equation

2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(g)

then we apply Hess's law to calculate the heat of reaction

ΔH rx = ∑ ν*ΔH products - ∑ ν*ΔH reactants , where ν represents the stoichiometric coefficient of products an reactants in the balanced equation

and express the number of moles that participate in the reaction,

Therefore

ΔH rx = ( 4*ΔH of CO₂ gas + 6*ΔH of H₂O vapor ) - (2*ΔH Ethane + 7*ΔH O₂ gas)

ΔH rx = [ 4mol* (-393,5 KJ/mol) + 6mol*(-241,826 KJ/mol) ] - [ 2mol*(-84,667KJ/mol) + 7mol* (0KJ/mol) ]

ΔH rx = -2855,622 KJ

The fact that is negative means that the reaction is exothermic (releases energy as heat)

Notes:

- ΔH products represents the enthalpy of formation of the products ( that is the enthalpy of reaction from the elements to form the compound). the same applies to ΔH of reactants

- ΔH of oxygen is set to 0, since by convention, the ΔH of an element in its standard form at standard conditions is 0. For oxygen its standard form is O₂ , and thus its ΔH =0 --> This implies that we are assuming that the reaction is carried out in standard conditions of temperature and pressure

- Since ΔH of reaction and also the ΔH products and reactants depend on the temperature of the reaction, this result is only valid for the Temperature that correspond to the ΔH of products and reactants given