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