Question

When heat is constantly supplied by a burner to boiling water, then the temperature of water during vaporisation (a) rises very slowly
(b) rises rapidly until steam is produced
(c) first rises and then becomes constant
(d) does not rise at all

Answer 1

(a) rises very slowly

Explanation:

The explanation for this question can be done in the following way,

• The first assumption that we take is boiling water is perfectly at 100°C .
• Now the heat given to boiling water at 100°C is first used into convertion to gas.
• The amount of heat that goes into this process is the latent heat of vapourization.
• After the heat given exceeds latent heat of vapourization the steam produced will have 100°C.
• Then on further heat the temperature of steam increase linearly.
• Now we notice that initially the temperature of the water didnt change much but as heat was being supplied and has changed its state the temperature increases again.
• In ideal case the temperature first remains constant and then increases.

Answer 2

Answer is Option (d)

Explanation:

• The temperature will only remain constant whilst the heat source is still being applied.
• The temperature of the water will not exceed 100 degrees because above this the water will no longer be a liquid, it will be in a gaseous state (steam).
• At the boiling point all the heat energy is being converted to kinetic energy, causing the particles to move faster, and as they reach the surface they will ‘escape’ the liquid and become gas particles.
• This will continue until all the particles have left the liquid state.