1. Chapter 11: Behavior of Gases

2. Particles of Ideal vs Real Gas
have no volume
have their own volume
don’t attract or repel each other
attract each other
have elastic collisions
have collisions that are not elastic

3. How gases behave Gas behavior is most ideal… at low pressures
at high temperatures
in nonpolar atoms/molecules
**Always use Kelvin temperatures when working with gases

4. Defining Gas Pressure
pressure of a gas is caused by the collisions of the particles in the gas on the walls of their container.

5. The more often gas particles collide with the walls of their container, the greater the pressure

6. Defining Gas Pressure
more air particles inside the ball mean more mass inside.

7. pressure of a gas is directly proportional to its mass. P α M
How are number of particles and gas pressure related?
pressure of a gas is directly proportional to its mass.
P α M
If m then p

8. How are temperature and pressure related?
At higher temperatures, the particles in a gas have greater kinetic energy.
move faster and collide with the walls of the container more often and with greater force, so the pressure rises.

9. If the volume of the container stays constant &
How are temperature and pressure related?
If the volume of the container stays constant &
# of particles of gas stays constant
Then pressure increases in direct proportion to the Kelvin temperature.

10. pressure of a gas is directly proportional to its Kelvin temperature.
How are temperature and pressure related?
pressure of a gas is directly proportional to its Kelvin temperature.
P α T
If t then p

11. Devices to Measure Pressure
barometer - instrument that measures the pressure exerted by the atmosphere.
The height of the mercury column measures the pressure exerted by the atmosphere

12. The Barometer
The standard atmosphere (atm) is defined as the pressure that supports a 760-mm column of mercury.
****remember atmospheric pressure decreases with altitude because the depth of air above you is less

13. Pressure Units
Atmospheric pressure is the force per unit area that the gases in the atmosphere exert on the surface of Earth.
The SI unit for measuring pressure is the pascal (Pa),

14. Pressure Units
Because the pascal is a small pressure unit, it is more convenient to use the kilopascal. 1 kilopascal (kPa) is equivalent to 1000 pascals.
1 atm = kPa

15. The Gas Laws
The gas laws apply to ideal gases, which are described by the kinetic theory

16. 2) If pressure decreases then volume increases
Boyle’s Law: Pressure and Volume
After performing many experiments with gases. Boyle had four findings.
at constant temperatures,
If pressure increases
then volume decreases
2) If pressure decreases
then volume increases

17. Boyle’s Law: Pressure and Volume
Boyle’s law states that the pressure and volume of a gas at constant temperature are indirectly proportional.
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18. Boyle’s Law
In mathematical terms, this law is expressed as follows.

19. P1 = initial pressure
V1 = initial volume
P2 = ending pressure
V2 = ending volume

20. Kinetic explanation of Boyle’s Law
At a constant temperature, the pressure exerted by a gas depends on the frequency of collisions between gas particles and the container.
If the same number of particles is squeezed into a smaller space (decreased volume), the frequency of collisions increases, thereby increasing the pressure.

21. Graph of Boyle’s Law pressure vs volume

22. Applying Boyle’s Law
A sample of compressed methane has a volume of 648 mL at a pressure of 503 kPa.
To what pressure would the methane have to be compressed in order to have a volume of 216 mL?
Examine the Boyle’s law equation. You need to find P2, the new pressure, so solve the equation for P2.

23. Applying Boyle’s Law
Substitute known values and solve.

24. Charles’s Law: Temperature and Volume
At constant pressure
If the temperature is increased,
if the volume is free to change, then
The volume increases

25. Charles’s Law
Charles’s law states that the volume and temperature of a gas at constant pressure are directly proportional
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26. Kinetic explanation of Charles’s Law
If the temperature is increased, average kinetic energy and particle movement increases and if volume is free to change it increases too

27. Graph of Charles’s Law volume vs temperature

28. Applying Charles’s Law
A weather balloon contains 5.30 kL of helium gas when the temperature is 12°C.
At what temperature will the balloon’s volume have increased to 6.00 kL?
Start by converting the given temperature to kelvins.

29. Applying Charles’s Law
Next, solve the Charles’s law equation for the new temperature, T2.

30. Applying Charles’s Law
Then, substitute the known values and compute the result.
Finally, convert the Kelvin temperature back to Celsius.
New Temperature = 323 – 273 = 50oC

31. T1 T2 GAY-LUSSAC’S LAW – pressure and temperature At constant volume
If the temperature is increased,
Then pressure increases
P1 = P2
T1 T2

32. GAY-LUSSAC’S LAW
Gay- Lussac’s law states that the temperature and pressure of a gas at constant volume are directly proportional

33. Kinetic explanation of Gay-Lussac’s Law
If the temperature is increased, average kinetic energy and particle movement increases and collisions occur more frequently, thereby increasing pressure

34. Boyle’s Law
Charles’s Law
Gay-Lussac’s Law
P1 = P2
T1 T2

35. “Potato Chips are Very Good To Bite.”
Pressure constant – Charles
Volume constant – Gay-Lussac
Temperature constant – Boyle

36. The Combined Gas Law
The gas laws may be combined into a single law, called the combined gas law, that relates two sets of conditions of pressure, volume, and temperature by the following equation.
With this equation, you can find the value of any one of the variables if you know the other five.

37. Applying the Combined Gas Law
A sample of nitrogen monoxide has a volume of 72.6 mL at a temperature of 16°C and a pressure of kPa.
What volume will the sample occupy at 24°C and 99.3 kPa?
Start by converting the temperatures to kelvins.

38. Applying the Combined Gas Law
Next, solve the combined gas law equation for the quantity to be determined, the new volume, V2.

39. Applying the Combined Gas Law
Substitute the known quantities and compute V2.

40. STP = Standard Temperature & Pressure
0°C and
1 atm

41. Avogadro’s Principle
Avogadro’s principle - equal volumes of gases at the same temperature and pressure contain the same number of particles.
An extension of Avogadro’s principle is that one mole (6.02 x 1023 particles) of any gas at STP (standard temperature and pressure -0°C and 1.00 atm pressure) occupies a volume of 22.4 L.
needs a multiply sign instead of an “x”

42. Applying Avogadro’s Principle
What is the volume of 7.17 g of neon gas at 24°C and 1.05 atm?
Start by converting the mass of neon to moles.
The periodic table tells you that the atomic mass of neon is amu. Therefore, the molar mass of neon is g.
needs a multiply sign instead of an “x”

43. Applying Avogadro’s Principle
Gases: Basic Concepts
Topic 13
Applying Avogadro’s Principle
Next, determine the volume at STP of mol Ne.
If you needed only the volume at STP, you could stop here.
Finally, use the combined gas law equation to determine the volume of the neon at 24°C and 1.05 atm pressure.
needs a multiply sign instead of an “x”

44. Applying Avogadro’s Principle
Gases: Basic Concepts
Topic 13
Applying Avogadro’s Principle
needs a multiply sign instead of an “x”

45. Basic Assessment Questions
Topic 13
Question 4
What pressure will be needed to reduce the volume of 77.4 L of helium at 98.0 kPa to a volume of 60.0 L?

46. Basic Assessment Questions
Topic 13
Answer
126 kPa

47. Basic Assessment Questions
Topic 13
Question 5
A sample of SO2 gas has a volume of 1.16 L at a temperature of 23°C. At what temperature will the gas have a volume of 1.25 L?

48. Basic Assessment Questions
Topic 13
Answer
46°C or 31.9 K

49. The End!