Question

When 1.552 g of liquid hexane (C₆H₁₄) undergoes combustion in a bomb calorimeter, the temperature rises from 26.32 °C to 38.67 °C. Find ΔErxn for the reaction in kJ/mol hexane. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.75 kJ/°C.

Answer 1

The change in energy (ΔErxn) for the combustion of hexane in a bomb calorimeter, with a temperature increase of 12.35 °C and heat capacity of 5.75 kJ/°C, is approximately 3945 kJ/mol.

Step-by-step explanation:

To find the change in energy (ΔErxn) for the combustion of hexane (C6H14), we first need to calculate the heat absorbed by the bomb calorimeter, then adjust it to a per mole basis. The temperature increase observed is from 26.32 °C to 38.67 °C, giving a change in temperature (ΔT) of 12.35 °C. The heat capacity of the bomb calorimeter (Ccal) is given as 5.75 kJ/°C.

The total heat (q) absorbed by the calorimeter is calculated as:

q = Ccal × ΔT

q = 5.75 kJ/°C × 12.35 °C

q = 71.0125 kJ

Next, we calculate the number of moles of hexane combusted. The molar mass of hexane is approximately 86.18 g/mol. Thus:

Moles of hexane = mass of hexane / molar mass of hexane

Moles of hexane = 1.552 g / 86.18 g/mol

Moles of hexane = 0.018 mol

Finally, to find the ΔErxn per mole of hexane:

ΔErxn = q / moles of hexane

ΔErxn = 71.0125 kJ / 0.018 mol

ΔErxn ≈ 3945 kJ/mol

This is the change in energy for the combustion of hexane per mole.