Final answer:
The motion of water molecules in a sealed cup at constant temperature remains constant. Energy transfer occurs from higher to lower temperature bodies, such as from hot water to ice. The system's entropy increases as it transitions from solid to liquid and as the temperature rises towards boiling. Option 1:
Step-by-step explanation:
If a cup of water is sealed and kept at a constant temperature, then the correct statement about the motion of the water molecules is that the motion remains constant. Water molecules are always in motion due to their kinetic energy, and this motion is directly related to temperature. In a sealed cup at constant temperature, there is no additional energy entering or leaving the system that would change the energy of the water molecules; therefore, their motion does not increase, stop, or become random but remains consistent.
When discussing the transfer of energy at the molecular level, it is important to note that energy transfer is from a higher temperature body to a lower temperature one. For example, when an ice cube is placed in hot water, energy flows from the hot water to the ice, resulting in the ice melting and the temperature of the water initially dropping.
Thermal equilibrium is reached when the temperature of the entire system becomes uniform. According to the zeroth law of thermodynamics, if two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other, and no net energy transfer will occur between them when they are combined.
With respect to entropy, the entropy of a system increases as it goes from solid ice (low entropy due to ordered structure) to liquid water (higher entropy due to less ordered structure). The system's entropy continues to increase as the water is heated towards its boiling point, where the molecules move more freely and the disorder increases.