Question

USE THE dimensional analysis method to solve: In Brazil, vehicles are fueled almost entirely by ethanol C2H6O, which is produced from sugar cane. Calculate the heat (in kJ) produced by ethanol for each 2.50 kg of CO₂produced.

Answer 1

first can sugar converts into glucose

C12H22O11 + H2O --------------> 2C6H12O6 ---------------->1

second glucose converts into ethanol and CO2

2C6H12O6 ------------------> 4C2H5OH + 4CO2 ---------------->2

overall reaction from 1 and 2

C12H22O11 (s) + H2O (l) ---------------> 4 C2H5OH   (l) + 4CO2 (g)

H = Hproducts - Hreactants

        = (4 x –393.5 + 4 x –277.7)- (–285.8 –2226.1)

        = -2684.8 + 2511.9

       = -172.9 kJ /mol

4 CO2 is produced : 4 x 44 = 176 g

for 176 g CO2 -------------------> -172.9 kJ /mol

     2.50 kg (2500 g) CO2 -------------> x kJ / mol

x = - 172.9 x 2500 / 176

x = -2456 kJ /mol

heat produced = - 2456 kJ /mol -----------------------------> answer