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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.
- Pressure (P) is the force (F) exerted per unit area (A).
- 1 atm = 760 mmHg = 760 torr = 14.7 psi = 101,325 Pa
- 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: P1V1=P2V2
- 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
- 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).
Combined Gas Law
- Shows the relationship of Pressure, Volume, and Temperature for a constant number of moles.
- 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).
- 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
Dalton's Law & Partial Pressures
- The total pressure (Ptotal) of a gas mixture is the sum of the partial pressures of its component gas.
- Equation for Total: Ptotal = A + B + C
- Equation for Partial: % of Gas = Decimal, THEN Decimal x Ptotal = 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: CH4, H2CO, H2O
- Strongest after Dispersion.
- Attractive forces between TWO POLAR molecules.
- Examples: H2CO, H2O
- Strongest after Dipole-Dipole
- Molecules containing H bonded to F, O, or N
- Examples: H2O
- Strongest out of all the intermolecular forces.
- Mixtures of ionic compounds and polar compounds.
- 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 (H2O) would have a HIGHER boiling point than London Dispersion (CH4)
- 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.