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Q. If number of molecules of $H_2$ are double than that of $O_2$, then ratio o f kinetic energy of hydrogen and that of oxygen at 300 K is

Kinetic Theory

Solution:

Mean Kinetic energy is given as, $K \cdot E =\frac{3}{2} nRT$ $n =$ no. of molecules.
$R =$ Constant.
$T =$ Temperature.
For $H _{2}$,
$ K \cdot E _{ H _{2}}=\frac{3}{2} n _{ H _{2}} RT \longrightarrow(1) $
For $_{2}$,
$ K \cdot E _{ O _{2}}=\frac{3}{2} n _{ O _{2}} RT \longrightarrow(1) $
On dividing equation (1) by equation (2) we get,
$ \frac{ K \cdot E _{ H _{2}}}{ K \cdot E _{ O _{2}}}=\frac{ n _{ H _{2}}}{ n _{ O _{2}}} $
given $n _{ H _{2}}=2 n _{ O _{2}}$,
$ \frac{ K \cdot E _{ H _{2}}}{ K \cdot E _{ O _{2}}}=\frac{ n _{2 O _{2}}}{ n _{ O _{2}}}=\frac{2}{1} $
Thus the ration is $2: 1$.