Question

How much PE does glucose have compared to gasoline (express as a percentage)?

Answer 1

Ans.       6CO₂ + 6 H₂O + Energy ----photosynthesis--------> C₆H₁₂O₆ + 6 O₂

According to first law of thermodynamics “energy can neither be created not be destroyed but can be transformed from one to another form”.

The potential energy (PE) of glucose can be defined as the amount of energy stored in its chemical bonds. During photosynthesis, the solar energy is conserved in form of chemical potential energy through the formation of glucose. The same chemical potential energy is released when glucose undergoes combustion or enter cellular respiration.

An easy measure of potential energy of the molecules is calorific value- the amount of energy released upon combustion of 1.0 gram of the sample. Since, combustion releases the potential energy in form of heat and light, it can be taken as a measure to determine how much energy was stored in the specified molecule- - following first law of thermodynamics.

Now,

                Calorific value of glucose = 16.3 kJ/ g

                Calorific value of gasoline = 47.3 kJ/g    

% PE in glucose compared to gasoline = (PE of glucose/ PE of gasoline) x 100

                                                                = (16.3 kJ g^-1 / 47.3 kJ g^-1) x 100

                                                                = 34.46 %