Thermochemistry Summary

Question

Butane (C4H10) has a standard of combustion of -2881 kJ mol^-1.

a. What is the significance of the negative sign associated with the enthalpy change?

b. calculate the change in enthalpy when 4.00 grams of butane is completely burned.

Answer 1

a) the negative sign means that the reaction (combustion of butane) is exothermic, meaning heat is given off or liberated during the reaction.

b) The combustion of C₄H₁₀ yield 288 kJ per mole. Calculate how many moles are in 4.00 g.

4.00 g C₄H₁₀ x 1 mol / 58 g = 0.0690 mols

Change in enthalpy = ∆H = 0.0690 mols x -288 kJ / mol = -19.9 kJ