Question

Ethanol (C2H5OH) burns in air to produce carbon dioxide and liquid water. Calculate the heat released (in kilojoules) per gram of the compound reacted with oxygen. The standard enthalpy of formation of ethanol is -277.7 kJ/mol.

Answer 1

Ans:- The balanced equation for the reaction is

C₂H₅OH (l) + 3O₂ (g) -> 2CO₂ (g) + 3H₂O (l)

Now, theoritically we know, standard enthalpy of formation for the following compound are as follows:-

H_f[C₂H₅OH] = -277.7 KJ/mol

H_f[O₂ (g) ] = 0 KJ/mol

H_f[CO₂ (g)] = -393.5 KJ/mol

H_f[H₂O (l) ]= -285.8 KJ/mol

molar mass of C₂H₅OH = 46.06 g/mol

Let us first calculate

= [2x(-393.5)+3x(-285.8)]

                           = -1644.4KJ/mol

= [(-277.7) + 3x0]

                             = -277.7 KJ/mol

              = -1644.4 - (-277.7)

              = -1366.7 KJ/mol

Energy released per gram of the compound

               = - 29.67 KJ/mol