Consider the combustion of liquid C₅H₈ in oxygen gas to produce carbon dioxide gas and water vapor.

Question

In an experiment, 0.1063 g of C₅H₈ is combusted to produce enough heat to raise the temperature of 150.0 g of water by 7.630 °C. If -4789 J of heat was produced from the combustion of 0.001561 moles of C₅H₈, what is the enthalpy change (in kJ/mol) for the combustion of C₅H₈?

Answer 1

q = mC∆T

q = heat = 4789 J

m = mass of water = 150.0 g

C = specific heat of water = 4.184 J/gº

∆T = change in temperature = 7.630º

Solving for q:

q = (150.0 g)(4.184 J/gº)(7.630º)

q = 4789 J heat from 0.001561 moles of C₅H₈

∆H_combustion = 4789 J / 0.001561 moles = 3,067,905 J/mol = 3068 kJ/mol (4 sig. figs.)