Question

When 1.550 g of liquid hexane (C6H14) undergoes combustion in a bomb calorimeter, the temperature rises from 25.87∘C to 38.13∘C. Find ΔErxn for the reaction in kJ/mol hexane. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.73 kJ/∘C. Express your answer in kilojoules per mole to three significant figures.2. The combustion of toluene has a ΔErxn of –3.91×103 kJ/mol. When 1.55 g of toluene (C7H8) undergoes combustion in a bomb calorimeter, the temperature rises from 23.12∘C to 37.57∘C. Find the heat capacity of the bomb calorimeter. Express the heat capacity in kilojoules per degree Celsius to three significant

Answer 1

Explanation:

1). The given data is as follows.

       $T_{i} = 25.87^{o}C$,      $T_{f} = 38.13^{o}C$

               C = 5.73 $kJ/^{o}C$

Hence, calculate the change in enthalpy of the reaction as follows.

      $\Delta E_{rxn} = -C \times \Delta T$

                     = $-5.73 \times (38.13 - 25.87)^{o}C$

                     = -70.25 KJ

As,  number of moles = $\frac{mass}{\text{molar mass}}$

                                    = $\frac{1.55}{(6 \times 12 + 14 \times 1)}$

                                    = 0.018 mol

Therefore, enthalpy of reaction in kJ/mol hexane is as follows.

            $\Delta E_{rxn} = \frac{-70.25 KJ}{0.018 mol}$

                          = $-3.90 \times 10^{3}$ kJ/mol

Thus, we can conclude that $\Delta E_{rxn}$ for the reaction in kJ/mol hexane is $-3.90 \times 10^{3}$ kJ/mol .

2).  As we know that,

     Number of moles = $\frac{mass}{\text{molar mass}}$

                                  = $\frac{1.55}{(7 \times 12 + 8 \times 1)}$

                                   = 0.017 mol

       $\Delta E_{rxn} = \E_{rxn} per mol \times \text{number of moles}$

                      = $-3.91 \times 10^{3} \times 0.017$

                      = -65.875 kJ

As,    $\Delta E_{rxn} = C \times \Delta T$

                    -65.875 kJ = $-C \times (37.57 - 23.12)^{o}C$

                           C = 4.56 $kJ/^{o}C$

Hence, heat capacity of the bomb calorimeter is 4.56 $kJ/^{o}C$.