Question

A container is partially filled with hot water, sealed and left to cool. Which statements are correct?
1. As the temperature decreases, water molecules lose kinetic energy.
2. As the temperature decreases, more water molecules move from vapour to liquid.
3. As the temperature decreases, the vapour pressure of the water decreases.
A.1, 2, 3 are correct
B.1 and 2 only are correct
C.2 and 3 only are correct
D.1 only is correct

Answer 1

Hint: To answer this question, analyze each statement systematically with respect to temperature. Changes in temperature are closely related to the kinetic energy of molecules. With decrease in temperature molecules move slowly and collide less.

Complete step-by-step answer: Let us analyze each of the statements systematically:
1.From Maxwell-Boltzmann Distribution we know that kinetic energy is directly proportional to temperature, hence, kinetic energy decreases on decreasing temperature and all molecular motion ceases if the temperature is reduced to absolute zero. Thus, statement 1 is correct.
2.Water vapor converts to its liquid form as the temperature decreases, as thermal energy decreases the molecules come closer in the liquid state. Thus, statement 2 is correct.
3.As the temperature increases, the vapor pressure of solid or liquid increases. Conversely, vapor pressure decreases as the temperature decreases. As the temperature decreases, the number of vapor molecules decreases. Water vapor converts to its liquid form as the temperature decreases. Hence, vapo1r pressure decreases with decrease in temperature. Thus, statement 3 is correct.
Therefore, from the above analysis we can conclude that the correct answer to this question is option A.

Note: When the temperature of a system is increased, the molecules bounce much more i.e. they have more energy. With increase in energy, they are more likely to collide. This means that more collisions will result in more tendency to combine.