Question

  If one could count one molecule per second, how many years would it take to count the molecules in a mole? (The number of molecules in a mole is Avogadro’s number N_A = 6 x 10²³.)

Answer 1

In one mole there are $6 \times10^{23}$ molecules. So, the time for counting

$$6 \times10^{23}\:\rm s=6 \times10^{23}\: \frac{1\: s}{365.2422*24*3600\frac{s}{year}}$$

$$=1.9\times10^{16}\:\rm years$$