how do the molecules differ in a cup of hot water and a cup of cold water?
a.) in the hot water molecules are moving faster than in the cold water
b.) in the hot water there are more molecules
c.) in the cold water the molecules are moving faster than in the hot water
d.) in the cold water there are more molecules
The correct answer and explanation is :
The correct answer is:
a.) in the hot water molecules are moving faster than in the cold water.
Explanation:
Water molecules, like all molecules, are in constant motion. This motion is a result of the thermal energy (heat) they possess, which directly affects the speed at which the molecules move. When you heat water, you are adding energy to it, causing the molecules to move faster. Conversely, when water is cold, the molecules have less energy and move more slowly.
Here’s a breakdown of how the molecular behavior changes in hot and cold water:
- Increased Motion with Heat:
- When water is heated, the molecules gain energy from the heat and move more rapidly. The faster the molecules move, the higher their kinetic energy. This increased motion leads to an increase in the frequency and intensity of collisions between molecules. This is why hot water is often seen to have a higher temperature – because the molecules are vibrating and moving faster.
- Molecular Speed in Cold Water:
- On the other hand, in cold water, the molecules have less energy, which results in slower movement. The molecules in cold water don’t collide with each other as often or as intensely as in hot water. This slower movement corresponds to a lower temperature.
- Why Option A is Correct:
- Option a, “in the hot water molecules are moving faster than in the cold water,” is correct because the speed of molecules in water is directly proportional to the temperature. When you heat water, the average speed of the molecules increases, and when you cool it down, their speed decreases.
Why the other options are incorrect:
- Option b (“in the hot water there are more molecules”): The number of molecules in a given volume of water doesn’t change with temperature. The molecules are just moving faster in hot water.
- Option c (“in the cold water the molecules are moving faster than in the hot water”): This is the opposite of what actually happens. The molecules in hot water move faster than in cold water.
- Option d (“in the cold water there are more molecules”): This statement is not accurate. The number of molecules remains constant regardless of the water’s temperature. What changes is the speed of their movement.
Thus, the correct understanding is that molecular motion increases with temperature. Therefore, hot water has faster-moving molecules compared to cold water.