Question

How do I calculate Energy (\[kcal/g\] ) if I know the Chemical formula, the \[kcal/mol\] , and the molar mass?

Answer 1

Hint: We need to know the difference between the two given units of energy and learn how to convert from one form of unit to another. There exist different units of energy keeping the basic definition of energy constant. The unit depends on the parameters used to measure it. The given unit is \[kcal/mol\] which is energy for one mole which is to be converted to \[kcal/g\] which is energy per gram. The parameters given for this conversion are Chemical formula, the \[kcal/mol\] unit and the molar mass of that substance.

Complete step by step answer:
We need to calculate Energy in \[kcal/g\] given the Chemical formula, the\[kcal/mol\] , and the molar mass. We know that \[kcal/mol\] is also a unit of energy. The only difference between the two is that one is the energy per mole of reaction and the other is energy per gram of a reaction.
By the definition of one mole of a substance which is Avogadro’s number of particles. Let us now define \[kcal/mol\] using a hypothetical reaction of one mole of reactants. After the complete reaction of one mole of reactants to produce a certain mole of products, the energy calculated will be in\[kcal/mol\] . Since we know the chemical formula and the molar mass, we can calculate the same energy in \[kcal/g.\]
The unit \[kcal/mol\] is basically \[kcal/g\] of molecular weight of the substance, i.e.,
\[kcal/g \times g/mol{\text{ }} = {\text{ }}kcal/mol\] or, \[kcal/g{\text{ }} = \] \[\dfrac{{kcal/mol}}{{g/mol}}\]
Here,\[g/mol\] is the molecular weight or the molar mass given.
Hence, the energy \[kcal/g\] can be calculated by simply dividing the energy in \[kcal/mol\] by the molecular weight of the substance.

Note:
It must be noted that the Joule is the proper SI unit of energy and calories or kilocalories are widely used by health professionals. The term kilocalorie (kcal) is also called Cal (the C must be capitalized). Hence 1 kcal/mol is also equal to 1 Cal/mol. Also, the term kcal/mol is defined as the amount of energy needed to warm 1 g of ${H_2}O$ by $1^\circ C$ . It is related to the standard unit of joules by the fact that $1cal = 4.14J$ .