Warm Up

1. A sample of an element is malleable and can conduct electricity. This element could be ____________________.

2. Ms Hughes wants to teach her class about the gold foil experiment. Which of the following models would best communicate the results of that experiment?

Announcements

• Unit 7 test this Friday (3/19)

• Stay on top of your grades this quarter- make sure you’ve taken unit 6 test (it’s really short!)

Welcome to fourth quarter!!!

Mystery Element

• #1: It is a gas.

• #2: Fills Valentine and birthday balloons.

• #3: Has atomic number 2

Take 1

Multiple Trials

• Doing an experiment multiple times or having multiple subjects

• Necessary to reduce error by taking the average

• Need a trial that has the control group (original form)

Gases

• Particles are:– Spread apart– In constant motion– Very small– Exert force on each other

when collide– Exert force on container

when collide

– Which is the gas?

Pumping a Bicycle Tire

• Imagine a flat tire with no air in it at all.

• Answer the following questions with a hypothesis– At the beginning, if you add more air by pumping the

tire, what will happen to the tire?• Describe what will happen to the pressure, temperature and

volume.

– Near the end (when the tire is almost full), if you add more air by pumping, what will happen to the tire?• Describe what will happen to the pressure, temperature and

volume.

An Ideal Gas

• When scientists study gases they assume the following– Gases consist of many particles that are far apart– Gas particles lose no energy when they collide– Gas particles are in continuous random motion– There are no intermolecular forces between gas particles

• Are any of these assumptions unrealistic? Why? – Support or reject each assumption with a complete

sentence.

Ideal vs. Real Gases

• Ideal gases act very closely to how real gases act– They are good approximations, but not perfect.

• Often times, scientists use ideal models instead of the real world.

• Answer the following in complete sentences– Why would a scientist use an ideal model instead of a real

model?– As a person who relies on scientists for information, do you

think it is okay for scientists to use models?

Gases are most like real gases when…

Temperature is HIGH

Volume is LOW

Why???

The Properties of Gases

• Let’s consider an ideal gas’s volume

• Write a hypothesis for each question below– How does pressure affect the volume of a gas?

– How does temperature affect the volume of a gas?

– How does the number of moles of gas affect the volume of a gas?

If…then…because…

Making an Equation

• Set volume (V) on the left side of the equation

• Consider each variable– If both increase at the same time they belong on opposite sides

of the equation.– If one increases and the other decreases they belong on the

same side.

• Create an equation with– V - Volume– P - Pressure– T - Temperature– n – number of moles

The Ideal Gas Law

• An ideal gas behaves according to the following equation

• R is the ideal gas constant

nRTPV

Kmol

kPaL

Kmol

atmL

Kmol

mmHgLR

314.80821.04.62

number of moles

The Units of R

• What can the units for pressure (P) be?– Which number could you use if the units were torr?

• What can the units for temperature (T) be?

• What can the units for volume (V) be?

• What can the units for moles (n) be?

Kmol

kPaL

Kmol

atmL

Kmol

mmHgLR

314.80821.04.62

Ideal Gas Law Problem

• What is the pressure in atmospheres exerted by a 0.500 mol sample of nitrogen gas (N2) in a 10.0 L container at 298 K?

To solve problems: we have to…

• Read the problem

• Identify what you know and don’t know.

• Write the formula/equation.

• Plug in numbers you know.

• Solve for what you don’t know know (using a calculator).

• Remember units!

A Harder One

• What pressure is exerted by a 0.325 mol of hydrogen gas in a 4.08 L container at 35K?A. 46.41 atm

B. 2.01 atm

C. 204.0 atm

D. 0.23 atm

E. 23.2 atm

Practice

1.A gas sample occupies 8.77 L at 20 K. What is the pressure, in atm, given that there are 1.45 mol of gas in the container?

2.What is the volume, in liters, of 0.250 mol of O2 at 20.0 K and 0.974 atm?

Complete the ideal gas laws worksheets

Remastery quiz

• Circle the correct answer

• Work silently and alone

Done Early?

• Start on homework

• Work quietly, be respectful

Sum up

• What did we learn today?

• HW:

• Top Ten: – How’d we do?