Gases, Liquids, Solids, and Intermolecular Forces

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Ralph Owens
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Liquids: The particles of a liquid are free to move within the confines of the

1 Chapter 6 Gases, Liquids, Solids, and Intermolecular Forces Solids: The particles of a solid have fixed positions and exhibit motions of vibration. Liquids: The particles of a liquid are free to move within the confines of the liquid. Gas: The particles of a gas are far apart and move randomly and rapidly. 6/2 1

2 Melting point (=freezing point): The temperature at which a solid becomes a liquid. Vaporization: The process of a liquid becoming a gas. Boiling point: The temperature at which the particles of a liquid escape and become a gas. 6/3 Condensation: The process by which a gas becomes a liquid. Freezing: The process by which a liquid becomes a solid. This occurs at the freezing point, which is the same as the melting point. Sublimation: When a solid changes directly from the solid to the gaseous state. 6/4 2

3 6/5 Ionic bonds: Ionic bonds are the strongest of forces that hold matter in the condensed states (liquids+solids). 6/6 3

4 Dipole forces: Polar molecules exist as dipoles. These oppositely charged ends will attract each other. solid liquid 6/7 Hydrogen bonds: When a hydrogen atom is covalently bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine (N,O,F), it can exhibit an additional polar attraction. This attraction is called a hydrogen bond. 6/8 4

Dispersion forces: Nonpolar molecules exhibit a dynamic induced dipole. The strength of this force increases with molecular weight and is known as dispersion forces or London dispersion forces.

5 Dispersion forces: Nonpolar molecules exhibit a dynamic induced dipole. The strength of this force increases with molecular weight and is known as dispersion forces or London dispersion forces. 6/9 Solution: An intimate, homogeneous mixture of two or more substances. Solute: A substance that is dispersed in a solution. Solvent: A substance doing the dissolving, usually present in greatest quantity. 6/10 5

6 6/11 Like dissolves like : Solutions form most readily when both the solute and solvent have similar intermolecular forces. oil and gasoline oil and vinegar 6/12 6

Ionic substances dissolve in water through iondipole interactions. 6/13 Kinetic Molecular Theory of a Gas Postulates: 1. The particles of a gas are in rapid constant motion. 2.

7 Ionic substances dissolve in water through iondipole interactions. 6/13 Kinetic Molecular Theory of a Gas Postulates: 1. The particles of a gas are in rapid constant motion. 2. The particles of a gas are tiny compared to the distance between them. 3. There is little attraction between the particles of a gas. 4. Collisions between gas molecules are perfectly elastic. 5. Temperature is a measure of the average kinetic energy of gas molecules. 6/14 7

8 Pressure = gas particles hitting the walls 6/15 Boyle s law: At constant temperature, the volume of a gas is inversely proportional to its pressure. V α 1/P V = a/p PV = a V 1 P 1 = V 2 P 2 6/16 8

9 Boyle s law: At constant temperature, the volume of a gas is inversely proportional to its pressure. 6/17 Charles s law: At constant pressure, the volume of a gas is directly proportional to its absolute temperature. V α T V = bt V/T = b V 1 /T 1 = V 2 /T 2 6/18 9

10 Charles s law: At constant pressure, the volume of a gas is directly proportional to its absolute temperature. 6/19 Charles s Law 6/20 10

11 Avogadro s law: At fixed temperature and pressure, the volume of a gas is directly proportional to the amount of gas. V α n V = cn V/n = c V 1 /n 1 = V 2 /n 2 6/21 Ideal gas law: PV = nrt R = L atm mol K 6/22 11

12 Ideal gas law: PV = nrt R = L atm mol K 6/23 Standard temperature and pressure: Standard temperature = 0 o C Standard pressure = 1 atm A mole of any gas at STP occupies 22.4 L 6/ L = 28.1 cm x 28.1 cm x 28.1 cm 12

Gases, Liquids and Solids

Chapter 5 Gases, Liquids and Solids The States of Matter Gases Pressure Forces between one molecule and another are called intermolecular forces. Intermolecular forces hold molecules together and kinetic