Gás ideal PV=nRT (pressão)

Ideal gas law: solving for pressure

The ideal gas law PV = nRT ties together the pressure, volume, moles and temperature of a gas. Solve it for pressure and you get P = nRT / V. The constant R is 0.0821 L·atm/(mol·K) when pressure is in atm, or 8.314 J/(mol·K) in SI. Take 1 mol of gas at 273 K (0 °C) packed into 22.4 L: that comes out to P = 1 atm, the textbook STP molar volume. Real gases drift away from this. At high pressure the molecules start to touch, and at low temperature their mutual attraction starts to count. When you're in either regime, switch to the van der Waals equation or to compressibility tables.

Applications

It runs through general chemistry in the stoichiometry of gaseous reactions, and through automotive engineering, where tire pressure climbs as the tire heats up (that's Gay-Lussac's law). Aerostatics leans on it for hot air balloons and for weather balloons that swell as they rise. You'll also find it in industrial chemistry with compressed reactors and pneumatics, and in scuba diving with compressed air tanks and decompression.

FAQ

Why must T be in Kelvin? The law is built on absolute temperature. Plug in Celsius and you'd get P = 0 at 0 °C, which is plainly wrong.

When does the model fail? Once you push past roughly 10 atm, or get close to the gas's condensation temperature. That's the point to switch to van der Waals.

STP vs SATP? The IUPAC STP used since 1982 sits at 273.15 K and 1 bar, giving a molar volume of 22.7 L. The older classic STP uses 273.15 K and 1 atm, which lands at 22.4 L.