Question

When 0.1523 g of liquid pentane (C5H12) combusts in a bomb calorimeter, the temperature rises from 23.7∘C to 29.8 ∘C. What is ΔUrxn for the reaction in kJ/mol pentane? The heat capacity of the bomb calorimeter is 5.23 kJ/∘C.​

Answer 1

Q cal = Ccal*delta T

= 5.23 KJ/oC*(29.8-23.7)oC

= 31.903 KJ

This heat is supplied by pentane

Molar mass of C5H12 = 5*MM(C) + 12*MM(H)

= 5*12.01 + 12*1.008

= 72.146 g/mol

mass of C5H12 = 0.1523 g

we have below equation to be used:

number of mol of C5H12,

n = mass of C5H12/molar mass of C5H12

=(0.1523 g)/(72.146 g/mol)

= 2.111*10^-3 mol

delta U = -Qcal/number of mol

= -31.903 KJ / 2.111*10^-3 mol

= -15113 KJ/mol

Answer: -15113 KJ/mol