Question

Write the balanced equation for the combustion of aqueous citric acid. Determine the standard molar enthalpy of aqueous citric acid. citric acid can constitute 8% of the dry weight of limes if a typical lime contains 30 ml of juice how much energy is released when one lime is combusted?

Answer 1

Solution :-

Balanced reaction equation

2 C₆H₈O₇ (aq)+ 9 O₂ (g) --- > 12 CO₂ (g) + 8 H₂O (g)   

Lets calculate the enthalpy of combustion of the citric acid

Delta H rxn = sum of delta Hf product – sum of delta Hf reactant

                     =[(CO2*12)+(H2O*8)] –[C6H8O7*2]

                     = [(-393.5 *12)+(-241.8*8)] – [-1544 *2]

                     = -3568.4 kJ

-3568.4 kJ * 1 mol citric acid / 2 mol = -1784.2 kJ/ mol

Now lets calculate the amount of the heat given by the burning of lime

(30 ml * 8 % /100%)*(1g /1ml) = 2.4 g citric acid

2.4 g citric acid * 1784.2 kJ per mol / 192.124 g per mol = 22.3 kJ

So 1 lime will give 22.3 kJ heat.