Question

Gram for gram, fats in food have much more chemical energy than sugar. One component of fat is stearic acid, C18H36O2. When a sample of 1.02 g of stearic acid was burned completely in a bomb calorimeter, the temperature of the calorimeter rose by 4.26oC. The heat capacity of the calorimeter was 9.43 kJ/oC. Calculate the molar heat of combustion of stearic acid in kilojoules per mole.

Answer 1

`\mathbf{-1.12 * 10^4 \ kJ/mol}`

Step-by-step explanation:

Given that:

mass (m) of the sample = 1.02 g

number of moles of stearic acid
`=(mass)/(molar mass)`

`= (1.02 \ g)/(284.49 \ g/mol) \\ \\ = 0.000358 \ moles`

The change in temp.
`\Delta T = 4.26^0 \ C`

heat capacity of the calorimeter (c) = 9.43 kJ/° C

Thus, heat due to reaction = cΔT

= 9.43 kJ/° C × 4.26° C

= 40.17 kJ

The heat in kJ/mol =
`(40.17 \ kJ)/(0.00358 \ mol)`

= 11204.23 kJ/mol

= 1.12 × 10⁴ kJ/mol

As a result of the reaction is exothermic, the heat reaction of the combustion is:

`\mathbf{-1.12 * 10^4 \ kJ/mol}`