Question

Ethanol (C2H5OH) is currently blended with gasoline as an automobile fuel.

A:Write a balanced equation for the combustion of liquid ethanol in air.

B:Calculate the standard enthalpy change for the reaction, assuming H2O(g) as a product.

C:Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of 0.789 g/mL.

D:Calculate the mass of CO2 produced per kJ of heat emitted.

Answer 1

Ethanol (C₂H₅OH) is currently blended with gasoline as an automobile fuel.

(A) Write a balanced equation for the combustion of liquid ethanol in air.

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

(B) Calculate the standard enthalpy change for the reaction, assuming H₂O(g) as a product.

▵H = ▵H (Products) - ▵H (Reactants)

▵H = (2(-393.5) + 3(-241.82)) - ((-277.7) + 3(0))

▵H = -1234.8 kJ

(C) Calculate the heat produced per liter of ethanol by combustion of ethanol under constant pressure. Ethanol has a density of 0.789 g/mL.

C₂H₅OH(l) + 3O₂(g) --->2CO₂(g) + 3H₂O(g) : ΔH = - 1234.8 kJ

Density of ethanol , d = 0.789 g/mL

1 mL of ethanol weighs 0.789 g

So , 1 L = 1000 mL of ethanol weighs 0.789 g/mL x 1000 mL = 789 g

Molar mass of C₂H₅OH = 46 g

46 g of ethanol on complete combustion the heat produced is 1234.8 kJ.

789 g of ethanol on complete combustion the heat produced is X kJ.

X = (1234.8 kJ x 789 g ) / 46 g

    = 21179.5 kJ

(D) Calculate the mass of CO2 produced per kJ of heat emitted.

Molar mass of CO₂ = 44 g

For the production of 2 x 44 g of CO₂ the heat produced is 1234.8 KJ

For the evolution of 1 kJ of heat the mass of CO₂ produced is = ( 2 x 44 ) / 1234.8

= 0.0712 g