Heptane is used in gasoline/automobile engineering as a standard with an "octane rating" of 0. The standard molar enthalpy of formation of n-heptane C7H16(l) is -187.9 kJ/mol. For the balanced reaction equation of heptane use: C7H16(l) + 11O2 --> 7CO2 + 8H2O.

Heptane is a liquid, but all the other chemicals in this reaction are gases. What is the enthalpy change of this reaction in kJ/mol?

Answer is: the equilibrium  shifts toward the reactants, to the left side of chemical reaction.it is because lead(ii) nitrate dissociates in water: pb(no₃)₂ → pb²⁺(aq) + 2no₃⁻(aq).according to lechatelier's principle, the position of equilibrium moves to counteract thechange (more lead cations, common ion), the position of equilibrium will move so that the concentration ofproducts decrease and concentration of reactants of chemical reaction increase.read more on -