Question

A 1.800-g sample of solid phenol (C6H5OH(s)) was burned in a bomb calorimeter, which has a total heat capacity of 11.66 kJ/∘C. The temperature of the calorimeter plus its contents increased from 21.36∘C to 26.37∘C.
(a)-Write a balanced chemical equation for the reaction that takes place in the bomb calorimeter. Express you answer as a chemical equation including phases. Water vapor, H2O(g), will initially form as part of this reaction. However, the temperature of all substances will eventually equilibrate in the bomb calorimeter (to 26.37∘C), which signifies that water and carbon dioxide, H2O(l) and CO2(g), are the eventual products of a combustion reaction in a bomb calorimeter.
(b)- What is the heat of combustion per gram of phenol?

Answer 1

Explanation:

(a)   When combustion of phenol takes place then it yields carbon dioxide and water.

A balanced chemical equation for this reaction is as follows.

    $C_{6}H_{5}OH(s) + 7O_{2}(g) \rightarrow 6CO_{2}(g) + 3H_{2}O(l)$

(b)   Heat released by combustion is equal to the total heat absorbed by the system (total content of calorimeter).

Therefore, heat released will be calculated as follows.

        Heat released = $C_{cal} \times \Delta T$

                                 = $11.66 kJ/^{o}C \times (26.37 - 21.36)^{o}C$

                                 = 58.4166 kJ

Hence, heat of combustion per gram phenol is as follows.

                    = $\frac{\text{-heat released}}{\text{mass of phenol}}$

                    = $\frac{-58.4166 kJ}{1.80 g}$

                    = -32.45 kJ/g

Therefore, heat of combustion per gram of phenol is -32.45 kJ/g.