You want a pot of water to boil at 105celcius. How heavy a

lid should you put on the 15 cm diameterpot when Patm =

101 kPa?

36 kg

Explanation:

For water to boil at 105 C it needs a pressure of 121 kPa (this is the vapor pressure of water at 105 C).

In the lid there will be a difference of pressure from one side to the other, this will be compensated by the weight of the lid.

Δp = pwater - patm

Δp = 121 - 101 = 20 kPa

The pressure caused by the weigh of the lid is:

Δp = w / A

Δp = m * g / A

Rearranging

m = Δp * A / g

m = Δp * π/4 * d^2 / g

m = 20000 * π/4 * 0.15^2 / 9.81 = 36 kg