Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Evaporation is the process of conversion of a liquid into its vapour state at any temperature below its boiling point.
It is a surface phenomenon, meaning particles from the surface gain enough energy to overcome the forces of attraction and escape into the air.
The rate of evaporation increases with an increase in surface area. For example, we spread out wet clothes to dry them faster.
The rate of evaporation increases with an increase in temperature, as more particles get enough kinetic energy to go into the vapour state.
The rate of evaporation decreases with an increase in humidity. Humidity is the amount of water vapour present in the air; if it is already high, the air cannot hold more moisture easily.
The rate of evaporation increases with an increase in wind speed, as wind moves the water vapour particles away, decreasing the amount of water vapour in the surroundings.
Evaporation causes cooling. This happens because the particles of the liquid absorb energy (Latent Heat of Vaporization) from the surroundings to regain the energy lost during evaporation.
📐Formulae
💡Examples
Problem 1:
Why does our palm feel cold when we put some acetone or perfume on it?
Solution:
The particles of acetone or perfume gain energy from our palm and the surroundings to evaporate. This energy is equal to the latent heat of vaporization.
Explanation:
As the acetone absorbs heat from the palm to turn into gas, the palm loses heat energy, resulting in a cooling sensation. This demonstrates the principle that evaporation causes cooling.
Problem 2:
Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Solution:
A saucer has a larger surface area compared to a cup.
Explanation:
Since evaporation is a surface phenomenon, the increased surface area in a saucer allows for a higher rate of evaporation. As evaporation causes cooling, the tea or milk in the saucer cools down much faster than in a cup.
Problem 3:
Convert to the Kelvin scale.
Solution:
Explanation:
To convert temperature from Celsius to Kelvin, we use the relation .