Question

You fill a tank with gas at 30°C and 101.5 kPa and seal it. You decrease the temperature to 10°C but keep the volume constant. What happens to the pressure? (Careful!

Answer 1

Assume that the gas that fills the tank is ideal for us to be able to use the ideal gas law.
PV = nRT
When V, n, and R are all constant, we can say that,
(T1)(P2) = (T2)(P1)
We convert temperature into kelvin (This is the portion where we have to be very careful not using the degrees Celsius).
(30 + 273)(P2) = (10 + 273)(101.5 kPa)
The value of P2 is 94.8 kPa.