Question

How much energy is utilised in the synthesis of one gram mole of glucose?
A. $673\;kcal$
B. $686\;kcal$
C. $666\;kcal$
D. $696\;kcal$

Answer 1

Hint: As we know that one mole is the definite amount of a substance which contains a fixed number of particles and six moles of carbon dioxide reacts with six moles of oxygen to produce one mole of glucose and six moles of water.

Complete answer:
As we know that one gram mole of any substance basically represents the molecular weight of that substance and we also know that if one mole of glucose is oxidised with six molecules of oxygen under standard conditions of temperature and pressure then it will result in the formation of six moles of carbon dioxide and six moles of water.
We know that the molecular weight of glucose is $180.2$ gram per mole so carbohydrates produces $3.8$ after oxidation so we can say that $1g$of glucose is oxidised to produce $3.8$ kilocalories per gram glucose molecule.
And $180.2$ gram mole of glucose will consume $3.8 \times 180.2 = 685$ kilo calories which is almost equal to $686\;kcal$.
Alternatively, since the breakdown of glucose involves the oxidation of glucose in the presence of oxygen to form six carbon dioxide molecules and six water molecules, the reaction produces $2870$kilojoules of energy for each mole of glucose which is metabolised. And we know that $1\;kJ = 0.24\;kcal$ to $2870$ kilojoules will be equal to $686\;kcal$ energy released per mole of glucose.
So, the correct answer is “Option B”.

Note:
Always remember that if molar mass is represented in an atomic mass unit then it represents the mass of only one molecule but if it is represented in gram then it depicts the mass of one mole of molecules which is commonly called gram molecular mass.