THE GAS LAWS

STATES OF MATTER  States of Matter  Solid state - particles(atoms, molecules, ions, etc) are rigidly stuck in place.  Particles vibrate, do not move past each other  Little space in between particles  Intermolecular forces of attraction are STRONG!  Liquid state – particles are able to slide past each other  Higher energy particles overcoming intermolecular forces of attraction  Little space in between particles  Gas state – particles are freely moving  Very high energy particles do not touch except when colliding  Plasma state also consists of high energy particles but are ionized(positively/negatively charged)  Huge space between particles

PHASES AND PHASE CHANGES Phase = state of matter Solid → liquid: melting Liquid → solid: freezing Liquid → Gas: vaporization (boiling) Gas → Liquid: Condensation Solid → Gas: sublimation Gas → Solid: deposition sublimation deposition vaporization Gas condensation SolidLiquid melting freezing

KINETIC MOLECULAR THEORY PREDICTING THE NATURE OF GASES  Postulates of the Kinetic Molecular Theory (KMT) 1.Gases consist of tiny particles (atoms or molecules). Mass is tiny, considered negligible(so small its effects are insignificant) 2.Particles are in constant, straight-line, random motion. Collisions with walls of its container create pressure 3.Particles have no attraction(or repulsion) to each other 4.Collisions are elastic – no energy is lost after collision 5.Average kinetic energy of the gas particles is directly proportional to its temperature in Kelvin Temperature = average kinetic energy

KINETIC MOLECULAR THEORY (KMT) KMT works when gases have ideal conditions –Low pressures –Lots of space between molecules –High temperatures –Fast moving particles –Nonpolar atoms/molecules –Less likely to stick to each other Real gases are not completely ideal –Real gases have volume & mass –Have some attraction for each other

PROPERTIES OF GASES  Pressure – the amount of force upon the area of a surface  Gas particles exert pressure by colliding with objects in their path.  The sum of all of the collisions makes up the pressure the gas exerts.

UNITS OF PRESSURE SI Unit: Pascals (Pa) 1 Pa = 1 Newton / square meter named for French mathematician/physicist/ inventor/writer/philosopher Blaise Pascal. Other units: atmospheres (atm) millimeters of mercury (mmHg) Torr (named for E. Torricelli, italian physicist) pounds per square inch (psi)

STANDARD PRESSURE Standard Pressure – normal air pressure at sea level Standard Pressure = 1 atm = 760 mmHg = kPa Converting pressure: 1 atm = 760 mmHg = kPa

TEMPERATURE Temperature – a measure of the average kinetic energy of a substance’s molecules. molecules in a hot object are moving faster than the molecules in a cold object on average! SI Unit for Temperature: °Celsius SI Unit for Absolute Temperature: Kelvin (no degree symbol!) Imperial Unit: °Farenheit To convert: from °C to K, add 273. from K to °C, subtract 273. EXAMPLES: Water boils at 100°C, or 373 K. Water freezes at 0°C, or 273 K. Avg. human body temp. is 37°C, or 310 K.

STANDARD TEMPERATURE Standard Temperature = 0°C or 273 K Absolute Zero = -273°C = 0 K. Lowest possible temperature. All molecular motion stops. Standard Temperature & Pressure: STP= 1.00 atm & 273K (0ºC)

PHASE DIAGRAMS Phase Diagram – A graph of pressure vs. Temperature of a substance and indicating where phase changes occur. Triple point : Where the substance exists in all three phases in equilibrium : all at the same time.

IDEAL GASES Perfectly obey the predictions made by the KMT: Molecules have no mass or volume. Molecules have zero intermolecular forces (Intermolecular forces cause molecules to ‘stick’ to each other and thus interfere with collisions) Collisions are always elastic. Real gases aren’t perfectly ideal. Some gases approach “idealness” under certain conditions: high temperature low pressure

PROPERTIES OF GASES

If pressure is measured in atmospheres(atm), R = If pressure is measured in kiloPascals(kPa), R = If pressure is measured in millimeters mercury/torr (torr), R = 62.4 L·atm mol·K L·kPa mol·K L·mmHg mol·K

MOLAR VOLUME OF GASES  What is the volume of 1 mole of a gas at STP(Standard Temperature and Pressure)? PV = nRT (1.00atm)(V) = (1.00mol)( )(273K) V = 22.4L Thus, 1 mole of any gas at STP is equal to 22.4L L·Atm Mol·K