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Properties of Gases

Properties of Gases. 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

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Properties of Gases

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  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

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