Properties of Gases

1. Properties of Gases

2. Basic features • Free move and fill any container it occupies homogeneously, continuously, and uniformly • Collection of molecules (or atoms) in random motion, with average speeds increasing as temperature raised • Except collisions, mostly the molecules are widely separated and weakly interacted with each other

3. States of gases: n, T, V, p • Equation of state: p=f(n,T,V)

4. States of gases: n, T, V, p • Equation of state: p=f(n,T,V)

5. The perfect gas law • Boyle-Marriote’s law: pV=constant, at constant n,T • Charles-Gay-Lussac’s law: • Vt=V0(1+at)=cT, at constant n,p • pt=p0(1+a’t)=c’T, at constant n,V • Avogadro’s principle: equal V at same T and p contains same number of molecules, or V∝n, at constant T,p Perfectgas (ideal gas) equation

6. The perfect gas law

7. Mixtures of gases: Dalton’s law • The pressure exerted by a mixture of ideal gases is the sum of the pressures to which each contributes as if it occupies the container alone. • pj=njRT/V=(nj/n)(nRT/V)=xjptotal

8. Real gases • Important at high p and low T, especially when close to condensing. • Size of molecules • Intermolecular interactions: Repulsive forces assist expansion thus increase pressure or volume, while attractiveforces assist compression thus decrease pressure or volume

9. The compression factor • Z=V/Videal=p/pideal =pV/(nRT) • Z1, when p0 • Z>1, when p is large enough (repulsions dominant) • mostly Z<1, when p is not too large (attractions dominant)

10. Boyle temperature • Z1, when p is small • High-T: Z>1 (repulsions dominant) • Low-T: Z<1 (attractions dominant)

11. Virialequation of state and virialcoefficients Z

12. Virial coefficients