January 15

Agenda

• Do Now (10 mins)• Pressure vs. Temperature (20 mins)• Pressure Quick Demo (5 mins)• Discuss Lab Tomorrow (15 mins)• Exit Question (5 mins)

Do Now: Using the diagram below, in your group attempt to solve for the remaining two boxes in the # of molecules row on your Stoichiometry Activity. We will discuss these problems as a class.

Molesgiven

Molesunknown

Mole-mole3-step

Conversion

Moleculesunknown

Moleculesknown

Divide by A’sNumber

Multiply by A’sNumber

A gas is a substance A gas is a substance thatthat Uniformly fills a Uniformly fills a

containercontainer Mixes completely with Mixes completely with

other gasesother gases Is easily compressedIs easily compressed

What is a gas?What is a gas?

The KINETIC MOLECULAR THEORY!The KINETIC MOLECULAR THEORY!

1. Gases consist of tiny particles (molecules or 1. Gases consist of tiny particles (molecules or atoms)atoms)

2. The particles are TINY compared to the 2. The particles are TINY compared to the space between them. Therefore, the volume space between them. Therefore, the volume of the individual particles is negligible (can be of the individual particles is negligible (can be considered ZERO).considered ZERO).

Itty-bittyItty-bitty Itty-bityItty-bitySpace between = BIGSpace between = BIG

KMT continuedKMT continued

3. The particles are in constant RANDOM 3. The particles are in constant RANDOM motion. The particles collide with the walls of motion. The particles collide with the walls of the container. These collisions result in the container. These collisions result in pressurepressure..

Exerts Exerts pressurepressure

Back to the KMT!

• 4. We assume the particles do not attract or repel each other.

• 5. The average kinetic energy (the energy of MOTION) of the particles is directly proportional to the temperature (the Kelvin temperature) of the gas.

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A closer look at Temperature:

– A gas at 00OC (such as O2) might move like this:

– A gas at 25OC room temperature might move like this:

– A gas at 100100O C (the temperature at which water boils) might move like this:

Why the differences in speed?

• The higher the temperature the gas is at, the more Kinetic Energy (KE) the gas molecules have (the faster they move!) Kinetic

Energy

Temperature

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So, to summarize, what variables, or factors, affect a gas?

• Pressure: the result of collisions of molecules on a surface

• Temperature: the average KINETIC energy of those molecules

• Volume: how much space the gas takes up

• Number of moles: how many molecules there are!

Let’s watch how these variables affect each other!

• http://www.chm.davidson.edu/ChemistryApplets/KineticMolecularTheory/PT.html

• http://www.teachertube.com/view_video.php?viewkey=5ea31ccc387f27523314

Talk about Tomorrow’s Lab

Exit Question

• When temperature increases, pressure ________.

• When temperature decreases, pressure ________.