Consider the molecule stearic acid (C18H36O2 and Mm = 284. g/mol) which is an an
ID: 951583 • Letter: C
Question
Consider the molecule stearic acid (C18H36O2 and Mm = 284. g/mol) which is an analogue of a carcass
fat found in the humps of certain camels. Suppose that complete metabolic combustion of a 0.306-g
sample of stearic acid raises the temperature of a 186.-mL sample of hexane (serving as a standard
calorimeter) by +2.79 ºC. Given that the specific heat of liquid hexane is 2.30 J/gºC, and its density is
0.655 g/mL, calculate the molar enthalpy of combustion for stearic acid in kJ/mol.
Hcomb = ____ ____kJ/mol
Explanation / Answer
Q = mcdT
= 0.306 g x 2.30 J/gºC x 2.79 ºC
= 1.963 J
Q = 1.963 J
Molar enthalpy of combustion for stearic acid = Q x Molar mass
= 1.963 J x 284 g/mol
= 557.5 J/mol
= 0.5575 kJ/mol