Explain the following a. When methylated spirit is poured on the skin, it has cooling effect, b. A piece of ice at 0 degree Celsius cools a drink more effectively than the same mass of cold water at 0 degree Celsius, c
Ice floats on water, d. Moisture is deposited on the outside of a glass bottle containing very cold water,
a. When methylated spirit is poured on the skin, it has a cooling effect because of its evaporation properties. Methylated spirit contains alcohol, which has a lower boiling point and evaporates more quickly than water. When it comes in contact with the skin, the alcohol molecules absorb heat from the skin to evaporate, causing a cooling sensation.
To explain this scientifically, the cooling effect is a result of the process called evaporative cooling. When a liquid evaporates, it goes through a phase change from a liquid to a gas. During this phase change, energy is required to break the intermolecular forces holding the liquid together. This energy is obtained from the surroundings, resulting in the cooling effect.
b. A piece of ice at 0 degrees Celsius cools a drink more effectively than the same mass of cold water at 0 degrees Celsius due to its latent heat of fusion. Latent heat is the energy absorbed or released during a phase transition without a change in temperature. In the case of ice, it undergoes a phase change from a solid to a liquid, and this phase change requires energy.
When the ice is placed in a drink, the ice absorbs heat from the drink to melt and transition from solid to liquid. This process requires a significant amount of energy since the latent heat of fusion of ice is relatively high. As a result, the drink cools down more effectively compared to the same mass of cold water, which does not undergo a phase change.
c. Ice floats on water due to its lower density compared to liquid water. Normally, substances become more dense as they solidify, causing them to sink in their liquid state. However, water is an exception.
The unique structure of water molecules allows for hydrogen bonding, which results in a crystal structure when water freezes. In this crystal structure, the molecules arrange themselves in a way that creates open spaces or empty pockets. These empty spaces cause the density of ice to be lower than that of liquid water.
Because ice is less dense, it floats on the surface of water. This floating phenomenon is important for the survival of aquatic organisms during winter, as the layer of ice acts as an insulating barrier protecting the water below from freezing completely, allowing life to continue beneath the ice.
d. Moisture is deposited on the outside of a glass bottle containing very cold water due to condensation. When warm air comes into contact with a cold surface, the air's temperature drops, reducing its ability to hold moisture in the form of water vapor. The excess moisture condenses and forms droplets on the cold surface.
In the case of a glass bottle containing very cold water, the cold temperature of the water reduces the temperature of the surrounding air near the bottle. This causes the moisture in the air to condense on the colder surface of the bottle, resulting in the formation of water droplets.
To prevent or reduce condensation on the outside of the glass bottle, insulation or wrapping the bottle with a material that reduces heat transfer can be used to prevent the bottle's temperature from decreasing and coming into contact with the cold air.