1. List 5 properties of gases 2. Identify the various parts of the kinetic molecular theory 3. Define pressure 4. Convert pressure into 3 different units 5. Define temperature 6. Convert a temperature to Kelvin

 Airbags fill with N 2 gas in an accident.  Gas is generated by the decomposition of sodium azide, NaN 3.  2 NaN 3 ---> 2 Na + 3 N 2

 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.

To Review  Gases expand to fill their containers  Gases are fluid – they flow  Gases have low density  1/1000 the density of the equivalent liquid or solid  Gases are compressible  Gases effuse and diffuse

Gas properties can be modeled using math. This model depends on —  V = volume of the gas (L)  T = temperature (K) › ALL temperatures in the entire unit MUST be in Kelvin!!! No Exceptions!  n = amount (moles)  P = pressure (atmospheres)

Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory.  Gases consist of tiny particles that are far apart relative to their size.  Collisions between gas particles and between particles and the walls of the container are elastic collisions  No kinetic energy is lost in elastic collisions

Ideal Gases Ideal Gases (continued)  Gas particles are in constant, rapid motion. They therefore possess kinetic energy, the energy of motion  There are no forces of attraction between gas particles  The average kinetic energy of gas particles depends on temperature, not on the identity of the particle.

Pressure  Is caused by the collisions of molecules with the walls of a container  Is equal to force/unit area  SI units = Newton/meter 2 = 1 Pascal (Pa)  1 atmosphere = 101,325 Pa  1 atmosphere = 1 atm = 760 mm Hg = 760 torr  1 atm = in Hg = 14.7 psi = bar = 10 m column of water.

Measuring Pressure The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17 th century. The device was called a “barometer” Baro = weight Meter = measure

An Early Barometer The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.

Column height measures Pressure of atmosphere 1111 standard atmosphere (atm) * = 760 mm Hg (or torr) * = inches Hg * = 14.7 pounds/in2 (psi) = kPa (SI unit is PASCAL) = about 34 feet of water!

OK, so it’s really not THIS kind of STP… STP in chemistry stands for Standard Temperature and Pressure Standard Pressure = 1 atm (or an equivalent) Standard Temperature = 0 deg C (273 K) STP allows us to compare amounts of gases between different pressures and temperatures

Let’s Review: Standard Temperature and Pressure “STP” P = 1 atmosphere, 760 torr T =  C, 273 Kelvins The molar volume of an ideal gas is liters at STP

A. What is 475 mm Hg expressed in atm? B. The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? = 1.52 x 10 3 mm Hg = atm 475 mm Hg x 29.4 psi x 1 atm 760 mm Hg 14.7 psi

kPa 14.7 psi A. What is 2.00 atm expressed in torr? B. The pressure of a tire is measured as 32.0 psi. What is this pressure in kPa? = 1520 torr 2.00 atm x 760 torr 1 atm = 221 kPa 32.0 psi x

Converting Celsius to Kelvin Gas law problems involving temperature require that the temperature be in KELVINS! Kelvins =  C °C = Kelvins - 273