Styrene, c8h8, is one of the substances used in the production of synthetic rubber. when styrene burns in oxygen to form carbon dioxide and liquid water under standard-state conditions at 25°c, 42.15 kj are released per gram of styrene. find the standard enthalpy of formation of styrene at 25°c.
(given: ? h°f[co2(g)] = –393.5 kj/mol, ? h°f[h2o(l)] = –285.8 kj/mol, ? h°f[h2o(g)] = –241.8 kj/mol)

ΔH°f(C₈H₈(l)) = 98.80 kJ/mol

Explanation:

Let's consider the combustion of styrene.

C₈H₈(l) + 10 O₂(g) → 8 CO₂(g) + 4 H₂O(l)

42.15 kJ are released per gram of styrene, that is, -42.15 kJ/g. In the balanced equation there is 1 mole of C₈H₈, so the heat released per mole is:

In order to find the standard enthalpy of formation of styrene (ΔH°f(C₈H₈(l))) we will use the following expression.

ΔH°rxn = Σ np . ΔH°f(p) - Σ nr . ΔH°f(r)

where,

ni: moles of reactants and products

ΔH°rxn = 8 mol × ΔH°f(CO₂(g)) + 4 mol × ΔH°f(H₂O(l)) - 1 mol × ΔH°f(C₈H₈(l)) - 10 mol × ΔH°f(O₂(g))

1 mol × ΔH°f(C₈H₈(l)) = 8 mol × ΔH°f(CO₂(g)) + 4 mol × ΔH°f(H₂O(l)) - 10 mol × ΔH°f(O₂(g)) - ΔH°rxn

1 mol × ΔH°f(C₈H₈(l)) = 8 mol × (-393.5 kJ/mol) + 4 mol × (-285.8 kJ/mol) - 10 mol × 0 kJ/mol - (-4390 KJ)

ΔH°f(C₈H₈(l)) = 98.80 kJ/mol

explanation: it gains negative electrons, therefore becoming negatively charged. as charge cannot be created, nor destroyed, only transferred, this leaves the wool positive. now that they have opposite charges, the two items attract.