CHEM&121 Exam 3: Chapter 7
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Properties of Gases
 A gas consists of particles  atoms/molecules  that move randomly & rapidly.
 The size of the particles are small compared to the space between them.
 Because the space is large, there are no attractive forces between them.
 The kinetic energy increases with increasing temp.
 When gas particle collide, they rebound. When they hit a wall, they exert pressure.

Gas Pressure
 Pressure (P) is the force (F) exerted per unit area (A).
 1 atm = 760 mmHg = 760 torr = 14.7 psi = 101,325 Pa

Boyle's Law
 Pressure and Volume
 For a fixed amount of gas at constant temperature, the pressure and volume of a gas are INVERSELY related (when one increases, the other decreases).
 The same number of gas particles occupies 1/2 the volume and exerts 2X the pressure.
 Equation: P_{1}V_{1}=P_{2}V_{2}

Charles's Law
 Volume and Temperature
 For a fixed amount of gas at constant pressure, the volume of a gas is PROPORTIONAL to its Kelvin temp (if one increases, the other will also).
 Equation for C to K: C + 273
 Equation:

GayLussac's Law
 Pressure and Temperature
 For a fixed amount of gas at constant volume, the pressure of a gas is PROPORTIONAL to its Kelvin temp (if one increases, the other will also).
 Equation:

Combined Gas Law
 Shows the relationship of Pressure, Volume, and Temperature for a constant number of moles.
 Equation:

Avogadro's Law
 Volume and Moles
 When the pressure and temperature are held constant, the volume of a gas is PROPORTIONAL to the number of moles present (when one increases, the other will also).
 Equation:

STP Conditions
 Pressure: 1 atm (760 mmHg)
 Temp: 273 K (0 degrees C)
 1 mole of any gas has the same volume as 22.4 L (Standard Molar Volume).

Ideal Gas Law
 Pressure, Volume, Temp, Universal gas Constant (R), and Moles
 Equation: PV=nRT
 R=0.0821

Dalton's Law & Partial Pressures
 The total pressure (P_{total}) of a gas mixture is the sum of the partial pressures of its component gas.
 Equation for Total: P_{total} = A + B + C
 Equation for Partial: % of Gas = Decimal, THEN Decimal x P_{total} = Partial Pressure

London Dispersion Forces
 Weakest of all the intermoleculars due to momentary changes in electron density in a molecule.
 Includes all molecules and atoms
 The larger the molecule, the larger the attractive force between two molecules and the stronger the intermolecular force.
 Examples: CH_{4}, H_{2}CO, H_{2}O

DipoleDipole Force
 Strongest after Dispersion.
 Attractive forces between TWO POLAR molecules.
 Examples: H_{2}CO, H_{2}O

Hydrogen Bonding
 Strongest after DipoleDipole
 Molecules containing H bonded to F, O, or N
 Examples: H_{2}O

IonDipole Force
 Strongest out of all the intermolecular forces.
 Mixtures of ionic compounds and polar compounds.

Boiling Point
 The temperature at which a liquid is converted to a gas phase.
 The increase in strength of the intermolecular forces, the increase in boiling points.
 Endothermic: energy is absorbed
 I.e. Hydrogen Bonding (H_{2}O) would have a HIGHER boiling point than London Dispersion (CH_{4})

Melting Point
 The temperature at which a solid is converted to a liquid phase.
 The increase in strength of the intermolecular forces, the increase in melting points.
 Endothermic: energy is absorbed.