# [thermo] pressure & steam tables related question

you want to boil a pot of water at 110 C
diameter of pot = 15cm
atmospheric pressure 101 kPa

what weight lid should you use?

i looked up the steam tables and water boils at 110 C at 143.27 kPa

so do i use that pressure or 143.27-101? (gauge pressure)

i used gauge and got something like ~76.14 kg.. which seems ridiculous for a lid weight

formula i used:

force = mass x 9.81
force = pressure * area
mass x 9.81 = pressure * area

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similar question but area = 5mm^2, atmospheric pressure = 101.3 kPa, and you want it to boil at 120 C

i got an answer of 0.101kg using absolute pressure and 0.049kg using gauge pressure

could you verify my answer and tell me which pressure i should be using.. absolute pressure or gauge pressure

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jack action
Gold Member
if you think about it, the force equilibrium is:

PinA = Wlid + PatmA

or

(Pin-Patm)A = Wlid
PgaugeA = Wlid

oh thanks you.. force equlibrium is a better way of looking at it :)