Question

When a 3.80 g sample of liquid octane (c8h18) is burned in a bomb calorimeter, the temperature of the calorimeter rises by 27.3 ∘c. the heat capacity of the calorimeter, measured in a separate experiment, is 6.10 kj/∘c . determine δerxn for the combustion of octane in units of kj/mol octane?

Answer 1

Δerxn  for  the combustion  of octate   in   kj/mol  is  4995.48  kj/mol

calculation

Step  1 :  calculate Δ T

ΔH  =  CΔT  where

 C=  specific heat capacity= 6.10 kj/°c

ΔT = change in temperature =  27.3 °c

ΔH  is  therefore =  27.3 °c  x  6.10  kj/°c  =166.53  kj

Step 2:  calculate ΔH   per  gram

ΔH   per  gram   of the sample=   166.53 kj/ 3.80 g  = 43.82  kj/g

Step: calculate ΔH  erxn  in  kj/mol

Δ H erxn  in kj /mol   =  43.82  x molar mass of C8H18The molar mass  of C8H18  is =  (12  x8)  +( 1 x18)  =  114 g/mol

Δ erxn is  therefore  = 43.82  kj/g  x 114  g/mol = 4995.48 kj/mol