Question
According to kinetic theory of gases, at absolute zero temperature
A.
water freezes
B.
liquid helium freezes
C.
molecular motion stops
D.
liquid hydrogen freezes
Answer :
molecular motion stops
Solution :
According to kinetic theory of gases, the pressure $$p$$ exerted by one mole of an ideal gas is given by
$$\eqalign{
& p = \frac{1}{3}\frac{M}{V}{c^2}\,\,{\text{or}}\,\,pV = \frac{1}{3}M{c^2} \cr
& {\text{or}}\,\,\frac{1}{3}M{c^2} = RT\,......\left( {\text{i}} \right) \cr} $$
where c is root mean square velocity of gas.
From Eq. (i), when $$T = 0,\,c = 0$$
Hence, absolute zero of temperature may be defined as that temperature at which root mean square velocity of the gas molecules reduces to zero. It means molecular motion ceases at absolute zero.