Question

A pure sample of pure 3-ethylhexane (C₈H₁₈) is combusted in a bomb calorimeter.

If the combustion of 5.50 g of 3-ethylhexane results in a rise in temperature from 37.29 °C to 44.00 °C, what is the heat capacity (in kJ/K) of the calorimeter? Report your answer to three significant figures.



The heat of combustion (ΔH°_c) for 3-ethylhexane is -5470.12 kJ/mol.

Answer 1

Heat capacity (calorimeter constant) of the calorimeter c= q/∆T

Given that heat of combustion of 3-ethylhexane = -5470.12 kJ/mol

mass of 3-ethylhexane = 5.5 g

Molar mass of 3-ethylhexane = 114 g/mol

Moles of the compound = mass of compund/ Molar mass of compound

= 5.5 g/114 g/mol

= 0.048 mol

Hence, Heat released to calorimeter q = ( 5470.12 kJ/mol)( 0.048 mol)

= 262.56 kJ

= 262.56 kJ

rise in temperature ∆T = 44.00 °C - 37.29 °C = 6.71 °C = 6.71 K

Hence, heat capacity (calorimeter constant) of the calorimeter

c=  q/ ∆T

= 262.56 kJ/ 6.71 K

= 39.13 kJ/K

c = 39.13 kJ/K

Therefore,  heat capacity (calorimeter constant) of the calorimeter = 39.13 kJ/K