question_answer 38)

                  A balloon has 5.0 g mole of helium at \[{{7}^{o}}C\]. Calculate                 (a) the number of atoms of helium in the balloon,                 (b) the total internal energy of the system.

Answer:

                  (a) Number of atoms of helium in the balloon                 \[=\mu N=\,5.0\,\times \,6.023\,\times \,{{10}^{23}}\]                 \[=3.0\times {{10}^{24}}\]                 (b) The Total internal energy = Number of atoms × average K.E. per atom                 \[=\,(\mu N)\,\times \,\frac{3}{2}\,kT\]                 \[=3\,\times \,{{10}^{24}}\,\times \frac{3}{2}\,\times 1.38\,\times {{10}^{-23}}\,\times 280\]                 \[=1.74\times {{10}^{4}}\,J\]