Essential Questions for Unit:

1. Essential Questions for Unit: • How do gases behave? • How are gases collected and studied? • What can we predict about gas behavior?

2. Introduction and reminder of gases • Fun fact: The word gas is derived from the Greek chaos • Gases consist of submicroscopic particles that are relatively far apart from each other moving randomly with an average K.E. proportional (∝) to the temperature. • Reminder: K.E. = Kinetic Energy

3. How are gases described? • Gases can be described in terms of four variables: • Pressure • Volume • Temperature • Amount (in moles) • The behavior of gases can be explained in terms of the kinetic molecular theory

4. Kinetic Molecular Theory (KMT) • Basic postulates (i.e. assumptions) of the KMT: • Gas particles are infinitely small • Gas particles are in constant, random motion • Or stated another way all collisions between particles in a gas are perfectly elastic • Gas particles don’t experience intermolecular forces • The kinetic energies of gas particles are proportional to their temperatures (in Kelvin)

5. Review: Properties of Gases • Gases have low densities • Gases can be easily compressed or expanded • Gases diffuse ** • Gases effuse** **Star these terms in your notes if you do not know what these terms mean or the difference between the two – we will come back to these properties later in the unit

6. Getting started with gas calculations Before we can start talking about how gases behave in numerical terms, we need to define some of the quantitative properties that are characteristic of gases

7. Pressure • Pressure (P): The force of gas molecules as they hit the sides of the container in which they are placed. • Common units of pressure: • atmospheres (atm): The average air pressure at sea level. • kilopascals (kPa): The SI unit for pressure; 101.3 kPa = 1 atm. • mm Hg (or Torr):760 mm Hg = 760 Torr = 1 atm. • Pounds per square inch: 14.7 psi = 1 atm • Summary: • 1.00 atm. = 101.3 kPa = 760 mm Hg or Torr= 14.7 psi

8. Volume • Volume (V): The amount of space in which a gas is enclosed. • The only commonly used unit of volume is liters (L). -- Lucky us!

9. Temperature • Temperature (T): A measurement of the amount of the average kinetic energy that the molecules have. The higher the energy, the higher the temperature. • Common units of temperature: • Kelvin (K): The only units that can be used when doing numerical problems with gases. • Degrees Celsius (0C): Must be converted to Kelvin before doing problems (by adding 273). • Temp in K = °C + 273

10. Other Terms Frequently Used: • STP: Stands for “standard temperature and pressure”, namely 273 K (00 C) and 1.00 atm (which is also 101.3 kPa). • “Room temperature”: 298 K (250 C)

11. Converting from one unit to another – a review • Look over the HW due for today. • How can we convert from one unit of pressure into the one desired for the problem? • What about temperature? • Volume? mL to L?

12. Gas Puns • Albert the German astronomer goes out tonight to watch the stars. “It must be cloudy,” he exclaims, “for I Xenon.” • Benny the burglar said, “It’s time that I made another Radon the bank.” • From: CHEM 13 NEWS, April 1980, p. 7

13. Various Gas Laws: A preview • The general gas law describes relationships among the variables (P, T, V, n) of an ideal gas. • Common relationships between these variables often described are: • Boyle’s law • Charles’ law • Gay Lussac’slaw • Avogadro’s law • Combined gas law • It should be noted that these are ALL subsetsof the ideal gas law

14. Can Demo • Please get out a separate sheet of paper to write on and turn in before you leave class • Please write any of your observations down during the demonstration • Please describe what you observed using any previous knowledge you have and related to anything we have discussed today in class. Be as specific as possible.

15. End of Introduction to Gases and Gas Law Unit HW for next class: Read pgs. 413-417, take 7 bullet notes