General Properties of Gases There is a lot of “free” space in a gas. Gases can be expanded infinitely. Gases fill containers uniformly and completely. Gases diffuse and mix rapidly.

Pressure The result of a force distributed over an area. SI unit for pressure = pascal (Pa) = N/m 2 (one kilopascal = kPa= 1000 Pa)

Atmospheric Pressure The pressure the earth’s atmosphere exerts due to its weight.

Pressure Pressure of air is measured with a BAROMETER Column height measures Pressure of atmosphere 1 standard atmosphere (atm) = 760 mm Hg = kPa (SI unit is PASCAL)

Measuring Pressure of confined gas Manometer- Instrument used to measure gas pressure Filled with Mercury

Variables that Affect the Properties of Gases CHEMSAVER P. 31 P = pressure (atm, mmHg, kPa) V = volume (ml, L, cm 3, etc) T = temperature (K) K = 0 C –ALL temperatures MUST be in Kelvin to calculate other variables!!! No Exceptions! n = amount (moles)

Standard Conditions STP- Standard Temperature and Pressure Standard Temperature: 273 K Standard Pressure: 1.00 atm (atmosphere)

Pressure Conversions 1.00 atm = kPa 1.00 atm = 760. mmHg 101.3kPa = 760. mmHg

Pressure Conversions A. What is 475 mm Hg expressed in atm? 1.00 atm 1.00 atm 760 mm Hg 760 mm Hg B. The pressure of a tire is measured as 29.4 kPa. What is this pressure in mm Hg? What is this pressure in mm Hg? 760 mm Hg 760 mm Hg 101.3kPa 101.3kPa = 221 mm Hg = atm 475 mm Hg x 29.4 kPa x

Click here for Demonstration Pressure and Volume

When temperature and the # of particles are kept constant in a closed container: When temperature and the # of particles are kept constant in a closed container: As Volume decreases, Pressure or As Volume increases, Pressure This is an relationship increases inverse decrease

A Graph of Boyle’s Law

Boyle’s Law P α 1/V This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant (do not change). For example, P goes up as V goes down. P 1 V 1 = P 2 V 2 P 1 V 1 = P 2 V 2 Robert Boyle ( )

Boyle’s Law If the gas is compressed to half the volume it had, twice as many molecules are present in any given volume. Twice as many impacts per second on the walls of the container results in doubling the pressure.

Boyle’s Law Example A balloon filled with Helium has a volume of 457ml at standard atmospheric pressure. After the balloon is released, it reaches an altitude of 6.3km where the pressure is only 65.5kPa. What is the volume of the balloon at this altitude? P 1 V 1 = P 2 V 2

Temperature and Volume Click here for Demonstration

Volume and Temperature Pressure and the # of particles are constant then As Temperature decreases, Volume _________ or or As Temperature increases, Volume __________ This is a relationship direct decreases increases

A Graph of Charles’s Law

Charles Law If n (moles) and P are constant, then V α T V and T are directly proportional. If one temperature goes up, the volume goes up! V 1 V 2 T 1 T 2 = Jacques Charles ( ) ( ) V 1 T 2 V 2 T 1 =

Charles’ Law Example A quantity of gas occupies a volume of 506 cm 3 at a temperature of 147 o C. Assuming that the pressure remains constant, at what temperature will the volume of the gas be 604 cm 3 ? V 1 = 506cm 3 V 2 = 604cm 3 T 1 = 147 o C =420KT 2 = ??

Charles’ Law Doubling the Kelvin temperature of a gas makes the gas expand resulting in doubling the volume of the gas

Pressure and Temperature Volume and the # of particles are constant then: As Temperature decreases, pressure _______ or or As Temperature increases, pressure ________ This is a relationship increase decrease direct

Gay-Lussac’s Law If n and V are constant, then P α T P and T are directly proportional. If one temperature goes up, the pressure goes up! = P 1 T 2 P 2 T 1 P 1 P 2 T 1 T 2 =

Guy Lussac’s Law Doubling the Kelvin temperature of a gas doubles the average kinetic energy of its molecules. Faster moving molecules strike the wall of the container more often and with more force doubling the Pressure.

Gas Pressure Temperature Volume Law (P) (T)(V) Boyles  constant  Charles constant   Gay- Lussac   constant CHEMSAVER P 31