Coal burns according to

The heat of combustion is of atomic carbon consumed. (a) We have to express this in terms of energy per carbon atom. (b) We have to express it in terms of energy per kilogram of the initial reactants, carbon and oxygen. (c) Suppose that the Sun were made of carbon and oxygen in combustible proportions and that it continued to radiate energy at its present rate of . We have to find how long it would last.

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(a)

Coal burns according to

The heat of combustion is of atomic carbon consumed. Mass of one carbon atom is 12.000 u.

Therefore, the number of atoms in 1.0 kg of carbon will be

The heat of combustion of carbon is of atomic carbon consumed. Therefore, energy per carbon atom will be

(b)

The mass of one carbon atom and one molecule will be 44 u. Therefore, combustion energy per kilogram of carbon and oxygen will be

(c)

In this model of the Sun, the total energy from combustion of carbon and oxygen that in principle can be obtained will be

We assume that the Sun is radiating energy at its present rate of . The life of the Sun in this model will therefore be