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Characteristics of Gaseous State

Characteristics of Gaseous State. Particles are very far apart Very weak interparticle forces Gases assume volume & shape of container Very compressible Flow readily Diffusion occurs rapidly Large free volume (99%, even at P=10 atm) Exhibit vibrational, rotational, translational motion

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Characteristics of Gaseous State

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  1. Characteristics of Gaseous State • Particles are very far apart • Very weak interparticle forces • Gases assume volume & shape of container • Very compressible • Flow readily • Diffusion occurs rapidly • Large free volume (99%, even at P=10 atm) • Exhibit vibrational, rotational, translational motion • Most energetic state of matter

  2. Characteristics of Liquid State • Particles are close together but not as close as in a solid • Particles exhibit vib. & rotational motion • Liquids are more energetic than solids but less energetic than gases • Liquids are negligibly compressible • Liquids assume shape of portion of container occupied • Flow readily & particles diffuse slowly • Liquids have 3% free volume • Moderately strong interparticle forces

  3. Characteristics of Solid State • Particles are very close together (most solids are close-packed) • Very strong interparticle forces • Most are crystalline • Some are amorphous (e.g., gels, plastics, glasses) • Least energetic state of matter • Particles exhibit only vibrational motion • Are incompressible • Retain own shape and volume • Extremely small free volume (<0.1%??) • Rigid • Diffusion occurs extremely slowly

  4. Composition of Matter • Matter is composed of: 1. Atoms 2. Ions 3. Molecules • Potential energy develops between particles 1. Results from attractive & repulsive forces called interparticle (I.P.) forces

  5. Interplay between I.P. forces & kinetic energy of particles causes:1. Properties of each state or phase2. Phase changes

  6. Kinetic-molecular view of states • Whether a substance is a gas, liquid, or solid is determined by interplay between: 1. P.E. of interparticle interactions P.E. = z1z2e2/r2 (Coulomb’s Law) 2. Kinetic energy of particles K.E. = EK=1/2 m2 where =3RT/MM

  7. Conditions for Liquefaction • T < Tcritical • P sufficient to bring molecules close enough for P.E.interparticle attractions > Ekinetic

  8. General types of electrostatic forces • Intramolecular a. Exist within each molecule or polyatomic ion b. Influence the chemical properties of the substance • Intermolecular (interparticle) a. Exist between atoms, molecules, or ions b. Influence the physical properties of the substance

  9. For example, the chemical behavior of water is identical in each of its three states because, in each state, its geometry is bent, it is polar, and the atoms in each water molecule are held together by the same intramolecular forces (polar covalent bonds) The physical behavior of water varies greatly because of the extent of interparticle forces (hydrogen bonds) in each state.

  10. The Critical Point When a liquid is heated in a closed container, boiling does not occur; instead temp. and vapor pressure rise continuously. Eventually critical point is reached. 1. dliq decreases & dvapor increases so that dliq = dvapor 2. Surface tension of liquid approaches 0 3. Meniscus disappears 4. Liquid and vapor become indistinguishable 5. Is highest temperature-pressure point on v. p. curve 6. Represents highest temp. at which the liq. can exist 7. Tcrit is temp. at critical point; Pcrit is pressure at critical point

  11. Consequences of Critical Point • Gases having Tcrit > room temp. can be liquefied by applying sufficient pressure. • Gases having Tcrit < room temp. can be liquefied by increasing pressure and lowering the temp. below Tcrit

  12. Some Tcrit and Pcrit Values SubstanceTcrit, KPcrit, atm H2 33.3 12.8 N2 126.2 33.5 O2 154.8 50.1 CH4 191.1 45.8 CO2 304.2 72.9 H2O 647.3 218.3

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