1. Gas Laws

2. Kinetic Theory and a Model for Gases
Gas particles travel in straight-line paths.
Gases share some general characteristics. a) The rapid, constant motion of particles in a gas causes them to collide with one another and with the walls of their container. b) The particles travel in straight-line paths between collisions. c) A gas fills all the available space in its container. 2

3. Gas Pressure
Gas pressure results from the force exerted by a gas per unit surface area of an object.
An empty space with no particles and no pressure is called a vacuum.
Atmospheric pressure results from the collisions of atoms and molecules in air with objects. 3

4. Gas Pressure The SI unit of pressure is the pascal (Pa).
One standard atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C. 4

5. Boyle’s Law
For a set amount of gas, if you keep the temperature constant, the volume will vary inversely with the pressure.
Basically, increase the volume- decrease the pressure
or decrease the volume-
increase the pressure.
The formula is:
P1 x V1 = P2 x V2
Robert Boyle ( ). Son of Earl of Cork, Ireland.

6. Knowns Unknowns V1=30 L He V2=? P1=103 KPA P2=25 KPA
A balloon contains 30L of Helium gas at 103kPa. What is the volume of the helium when the balloon rises to an altitude where the pressure is only 25 kPa? (Assume the temperature remains constant)
Knowns Unknowns V1=30 L He V2=? P1=103 KPA P2=25 KPA
* Hint- the originals are always paired together
V2= (P1) (V1) P2

7. Charles Law
As the temperature of an enclosed gas increases, the volume increases, if the pressure remains constant
The volume of a fixed mass of gas is directly proportional to its Kelvin temperature it’s pressure remains constant
The formula is: V1 = V T1 T2
Temperature is measured in Kelvin's where 0 Celsius equals 273 k.
Jacques Charles ( ). Isolated boron and studied gases. Balloonist.

8. Knowns Unknowns V1= 4.00 L V2= ? T1= 24 C T2= 58 C
A balloon inflated in a room at 24 degrees Celsius has a volume of 4.L. The balloon is then heated to a temperature of 58 degrees C. What is the new volume if the pressure remains constant?
Knowns Unknowns V1= 4.00 L V2= ? T1= 24 C T2= 58 C
1st: need to convert temperature to kelvin!
C = K
V2= (V1) (T2) T1

9. Gay-Lussac’s Law
The pressure of a gas is directly related to the temperature. If you increase the temperature you increase the pressure. If you decrease the temperature, you decrease the pressure. So P1 = P2 T1 T2

10. Knowns Unknowns P1= 103 KPA P2= ? T1= 25 C T2= 928 C
The gas in a used aerosol can is at a pressure of 103 kPa at 25 degrees Celsius. If the can is thrown into a fire, what will the pressure be when the temperature reaches 928 degrees Celsius?
Knowns Unknowns P1= 103 KPA P2= ? T1= 25 C T2= 928 C
1st- convert temperatures to kelvin!
C = K
P2= (P1) (T2) T1

11. The Combined Gas Law
Allows you to do calculations for situations in which only the amount of gas is constant.
It shows the relationship between Temp, Pressure, and Volume.
Here: P1 x V1 = P2 x V T T2

12. Knowns Unknowns P1= 153 KPA V2= ? V1= 30 L T1= 313 K P2= 101.3 KPA
The volume of a gas-filled balloon is 30 l at 313 k and 153 kPa pressure. What would the volume be at standard temperature and pressure (STP)?
P1 x V1 = P2 x V2
T T2
Knowns Unknowns
P1= 153 KPA V2= ?
V1= 30 L
T1= 313 K
P2= KPA
T2= 0 C
(need to convert Celsius to kelvin)
C = K
V2= V1 x P1 x T2
P2 x T1

13. Ideal Gas Law Ideal vs. Real
No volume some volume
No Inter-molecular forces some Inter-molecular forces
Up to this point the amount of gas has been held constant.
The Ideal Gas Law allows us to consider varying the amount of gas while also messing with the temp, pressure, and volume.

14. The Ideal Formula P V = n R T P = pressure in kPa V = volume in liters
T = temp in Kelvin
R is the constant 8.31 (L x kPa)/(K x mol)
n = number of moles

15. A deep underground cavern contains 2
A deep underground cavern contains 2.24 x 10^6 L of methane gas (CH4) at a pressure of 1.5 x 10^3 kPa and a temperature of 315 K. How many moles of CH4 does the cavern contain?
Knowns Unknowns P= 1.50 x 10^3 kpa kg CH4 V= 2.24 x 10^6 L T= 315 K R= 8.31 (L x kpa)/(K x mol) Molar Mass CH4= 16g n= P x V R x T

16. Learning Check
When the temperature of a rigid hollow sphere containing 685 L of helium gas is held at 621 K, the pressure of the gas is 1.89 x 10^3 kPa. How many moles of helium does the sphere contain?

17. One More Practice Problem
A newborn lamb’s lungs can hold 2.20 L. How many grams of air do her lungs hold at a pressure of 102 kPa and a body temperature of 37 degrees C? Use a molar mass of 29g for air, which is about 20% O2 (32 g/mol) and 80% N2 (28 g/mol)

18. According to the kinetic theory, collisions between molecules in a gas
A. are perfectly elastic
B. are inelastic
C. never occur
D. cause a loss of total kinetic energy

19. What instrument is normally used to measure atmospheric pressure?
A. thermometer
B. Barometer
C. Vacuum
D. manometer

20. Standard Conditions when working with gases are
A. 0 k and kpa
B. 0 k and 1 kpa
C. 0 C and kpa
D. 0 C and 1 kpa

21. How does the atmospheric pressure at altitudes below sea level compare with atmospheric pressure at sea level?
A. The atmospheric pressure below sea level is higher
B. the atmospheric pressure below sea level is lower
C. the pressures are the same
D. differences in pressure cannot be determined

22. What causes pressure in a container such as a helium balloon?
A. the walls of a container
B. the vacuum maintained in the container
C. the simultaneous collisions of fast-moving particles in the container
Atmospheric pressure acting on the outside walls of the container

23. The temperature at which the motion of particles theoretically ceases is
A K
B. 0 k
C. 0 degrees celcius
D. 273 degrees celcius

24. What happens to the temperature of a liquid as it evaporates?
A. it increases
B. it decreases
C. it does not change
D. the change cannot be determined

25. A. it is greater than the rate of condensation
In a dynamic equilibrium between the liquid state and the gas state, what is true about the rate of evaporation?
A. it is greater than the rate of condensation
B. it is less than the rate of condensation
C. it is equal to the rate of condensation
D. the rate of evaporation cannot be determined

26. Whys is a gas easier to compress than a liquid or a solid?
A. its volume increases more under pressure than an equal volume of liquid does
B. its volume increases more under pressure than an equal volume of solid does
C. the space between gas particles is much less than the space between liquid or solid particles
D. the volume of a gas’s particles is small compared to the overall volume of a gas

27. How does a gas propellant move when an aerosol can it used?
A. from a region of high pressure to a region of low pressure
B. from a region of high pressure to a region of equally high pressure
C. from a region of low pressure to a region of higher pressure
D. from a region of low pressure to a region of equally lower pressure

28. A. It increases by a factor of 4 B. it decreases by a factor of 8
The volume of a gas is reduced from 4 L to .5 L while the temperature is help constant. How does the gas pressure change?
A. It increases by a factor of 4
B. it decreases by a factor of 8
C. it increase by a factor of 8
D. It decreases by a factor of 2

29. If a balloon is heated, what happens to the volume of the air in the balloon if the pressure is constant?
A. it increase
B. it stays the same
C. it decreases
D. The change cannot be predicted

30. As the temperature of a fixed volume of gas increases, its pressure will
A. vary inversely
B. decrease
C. not change
D. increase

31. A gas occupies a volume of 2. 4 L at 14. 1 kpa
A gas occupies a volume of 2.4 L at 14.1 kpa. What volume will the gas occupy at 84.6 kpa?
A. 497 L
B. 2.5 L
C. 14 L
D. .40 L

32. A sample of gas occupies 17 ml at -112 degrees Celcius
A sample of gas occupies 17 ml at -112 degrees Celcius. What volume does the sample occupy at 70 degrees celcius?
A. 10.6ml
B. 27 ml
C. 36 ml
D. 8.0 ml

33. In general, for a gas at a constant volume,
A. the pressure of the has is inversely proportional to its temperature in kelvins
B. the volume of the gas is inversely proportional to its temperature in kelvins
C. the volume of the gas is directly proportional to its temperature in kelvins
D. the pressure of the gas is directly proportional to its temperature in kelvins

34. The combined gas law relates which of the following?
A. pressure and volume only
B. temperature and pressure only
C. volume and temperature only
D. temperature, pressure, and volume