Question

Assertion: When ice and water are kept in a perfectly insulated thermos flask at 273 K and the atmospheric pressure, there is no change in mass of ice and water.
Reason: The system is in static equilibrium.
A.If both assertion and reason are true and the reason is the correct explanation of the assertion
B.If both assertion and reason are true and the reason is not the correct explanation of the assertion
C.If the assertion is true but the reason is false
D.If both assertion and reason are false

Answer 1

Hint: A static equilibrium means that the reaction occurring in a system is completely halted and there exists no movement between the reactants and the products corresponding to the chemical reaction.

Complete step by step answer:
An equilibrium is established during the liquefaction of ice to water. The rates of conversion of the molecule from ice to water and from water to ice will remain the same at a given temperature and atmospheric pressure so the mass of ice and water does not change. When ice and water are placed in contact, two processes take place simultaneously: first, particles on the surface of the ice escape into the water (melting), and second process, that the particles of water are captured on the surface of the ice (freezing). A point is achieved when the rate of freezing is the same as the rate of melting, the amount of ice and the amount of water won't change on average. As the particles are in a constant state of motion, the ice and water are said to be in dynamic equilibrium and not static.

Therefore, we can conclude that the correct answer to this question is option C.
Note:
This balance achieved between freezing and melting processes can easily be upset. This can occur when the ice/water mixture is cooled, the molecules move slower. Hence, the slower-moving molecules are more easily captured by the ice, and freezing occurs at a greater rate than melting. Also, heating the mixture makes the molecules move faster on average, and melting is favoured. Addition of foreign molecules can also cause disruption in the packing arrangement of ice molecules.