Question

What is the boiling point of water at the top of a mountain?
100
a.) > 100 since the pressure is less than at ground level
b.) < 100 since the pressure is less than at ground level
c.) > 100 since the pressure is greater than at ground level
d.) < 100 since the pressure is greater than at ground level

Answer 1

Hint: Before solving this question, keep in mind that pressure has an inverse relation with altitude. As we go higher, i.e. above the mean sea level, the pressure keeps on decreasing. This can be observed by difficulty in breathing when one goes to a hill station.

Complete step by step answer:
Boiling point of water at mean sea level is 100-degree Celsius. The atmospheric pressure is 1 atm.
As we go higher in altitude, the pressure decreases, because the number of air molecules decreases.
Now we can relate pressure to temperature according to Gay Lussac’s law as – “pressure of a given amount of gas held at constant volume is directly proportional to the temperature”.
Therefore, as pressure decreases, so will the temperature needed to boil water.
Therefore, the answer is option (c) the boiling point of water at the top of a mountain is < 100 since the pressure is less than at ground level.

Additional Information:
As we go higher, i.e. above the mean sea level, the temperature also keeps on decreasing. That is why hilly regions are cooler.

Note: You can also solve this question by applying the ideal gas law in this case by relating pressure and temperature. As we know, pressure increases with altitude. According to the Ideal Gas equation, PV = nRT, therefore, pressure is directly proportional to temperature. As pressure decreases, so does temperature.