Question

The average kinetic energy of water molecules is greatest in which of these samples?(1) 10 g of water at 35°C(2) 10 g of water at 55°C(3) 100 g of water at 25°C(4) 100 g of water at 45°C

Answer 1

Answer : The correct option is, (2) 10 g of water at 55°C

Explanation :

Average kinetic energy of the gas particle is directly proportional to the temperature of the gas particle.

Formula used :

$K.E=\frac{3}{2}\frac{RT}{N_A}$

where,

R = Gas constant

T = temperature

$N_A$ = Avogadro's number

From this we conclude that the kinetic energy is directly proportional to the temperature where 'R' and $N_A$ are constant. That means kinetic energy depends only on the temperature not on the mass.

(Higher the temperature, higher will be the kinetic energy)

Hence, the average kinetic energy of water molecules is greatest in 10 g of water at 55°C.

Answer 2

The question asks about the average kinetic energy so it is not related with mass. We only need to compare the temperature. The higher temperature is, the higher kinetic energy is. So the answer is (2).