Thermal Properties Of Matters (BOILING AND EVAPORATION)

Question 1

EXPLANATION OF HOW EVAPORATION OCCURS

Answer 1

Molecules that are NEAR THE SURFACE of the liquid AND possess higher KE are able to escape into the air, leaving the less energetic molecules behind.
∙ Average KE of the liquid molecules becomes lower, and the temperature of the liquid decreases.
∙ Thermal energy from the surrounding is transferred to the liquid from a region of higher temperature to a region of lower temperature.
∙ The KE of the molecules increases and the first step is repeated.

Question 2

FACTORS AFFECTING EVAPORATION

Answer 2

1. Temperature
   The higher the temperature, the higher the rate of evaporation. The average kinetic energy of molecules are higher and they can escape from the surface of the liquid more readily.
2. Area of exposed surface
   The greater the area of exposed surface, the higher the rate of evaporation. More molecules are able to escape the surface at the same time.
3. Humidity of surrounding air
   The less humid the surrounding air, the higher the rate of evaporation. There is a larger concentration gradient of gas molecules between the region above the liquid surface and the surrounding air. Diffusion of gas molecules occurs more readily, allowing for evaporation to continue.
4. Motion of air
   The faster the surrounding air, the higher the rate of evaporation. Gas molecules above the liquid surface can be blown away, maintaining the concentration gradient of gas molecules.
5. Pressure
   The lower the external air pressure, the higher the rate of evaporation. A low surrounding air pressure allows more molecules to escape the liquid surface and avoid collision by the air molecules back into the liquid.
6. Nature of liquid
   The more volatile the liquid, the higher the rate of evaporation. Molecules are more likely to escape a volatile liquid