Question

When 1.542 g of liquid hexane (C6H14) undergoes combustion in a bomb calorimeter, the temperature rises from 25.71 ∘C to 38.91 ∘C. Find ΔErxn for the reaction in kJ/mol hexane. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.76 kJ/∘C .

Answer 1

we know that

moles = mass / molar mass

also

molar mass of hexane = 86

so

moles of hexane = 1.542 / 86 = 0.01793

now

we know that

heat = heat capacity x temp change

given

heat capacity = 5.76 kJ / C

so

heat = 5.76 x 1000 x ( 38.91 - 25.71)

heat = 76032 J

now

this heat is produced by the combustion of hexane

so

dErxn = heat / moles of hexane

so

dErxn = 76032 / 0.01793

dE rxn = 4240 x 10^3

so

dE rxn = 4240 kJ

as heat is produced , it should be -ve

so

dE rxn is -4240 kJ