Question

At Darjeeling, distilled water boils at a temperature____.
(A) Above 373K
(B) Above 473K
(C) Below 373K
(D) At 373K

Answer 1

Hint: The boiling point of a substance is directly proportional to the pressure. So, to answer this question we will have to consider the atmospheric pressure of the place.

Complete answer:
Let’s look at the answer:
First we will define boiling point.
> The temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure is called a boiling point.
> Now, at high altitudes the atmospheric pressure is low as the air is thin. So, the vapour pressure of the liquid will get equal to the atmospheric pressure faster and the liquid will start boiling at a temperature lower than its normal boiling temperature.
> Now, we know that, at standard pressure which is 1 atmosphere, water boils at 373K.
Darjeeling is located at high altitude. So, the atmospheric pressure in Darjeeling will be lower than 1 atmosphere. So, if we boil distilled water at high altitude, the vapour pressure of the water will become equal to the atmospheric pressure at a lower temperature than its normal boiling temperature.
Therefore, at Darjeeling water will boil at a temperature below 373K.

Hence, the answer to the given question is option (C).

Additional Information: As we got to know from the above paragraph that boiling point and evaporation is dependent on pressure and boils at lower temperature with decrease in atmospheric pressure. It should also be noted that this is the reason why food takes longer to be cooked in mountainous areas i.e at higher altitudes.

Note: Students should remember the boiling point of water at standard conditions. The atmospheric pressure is related to altitude. Higher the altitude lower is the atmospheric pressure and lower the altitude higher is the atmospheric pressure.