The Ideal Gas Law

Real Gas Behaviour There are several assumptions in the kinetic molecular theory that describe an ideal gas Gas molecules have zero volume Forces of attraction/repulsion are zero Molecules move in straight lines Collisions are completely elastic However, at high pressure and low temperature there are problems with these assumptions In very small volumes there will be many more interactions and collisions The volumes of the gas molecules is now a significant fraction of the container

Real Gas Ideal Gas In some cases (polar molecules), mild attractions exist between particles (volume is mildly decreased) No attractions exist between particles (no IMF) Gas particles occupy space Gas particles have no volume Some gases do condense at low temperature and high pressure Ideal gases will NOT condense into liquid “Mostly” obey the gas laws Obey gas laws perfectly Constant RANDOM motion Motion of particles is always in straight lines

The Ideal Gas Law Boyle’s Law: PV = k or V = k P Charles’ Law: V = k or V = aT T Avogadro’s Law: V = b or V = bn n V = kab X nT V = RnT or PV = nRT

PV= nRT Unit Analysis! P = pressure (kPa) V = volume (L) PV = nRT R = PV nT R = (kPa)(L) (mol)(T) R = 8.314 kPa·L/mol·K P = pressure (kPa) V = volume (L) n = amount (mol) T = temperature (K) R = ??

Try These… Use the ideal gas law to calculate the molar volume of a gas at SATP. A cylinder of laughing gas (N2O) has a diameter of 23.0 cm and a height of 140 cm. The pressure is 108 kPa at a temperature of 294 K. How many grams of laughing gas are in the cylinder? Hint: Vcylylinder = r2h

Homework Read p. 443-445 P. 445 #3,4,6 P. 448 #1-6