1. Chemistry I Mr. Patel SWHS
Unit 10: Gases
Chemistry I
Mr. Patel
SWHS

2. Topic Outline MUST have a scientific calculator (not graphing)!!
Properties of Gases (13.1, 14.1)
Kinetic Molecular Theory (13.1)
Temperature Conversions (14.1)
Pressure Conversions (14.1)
Empirical Gas Laws (14.2)
Ideal Gases (14.3)

3. Nature and Properties of Gases
Gases are easily compressible
Flow easily (fluids)
Assume the shape and volume of container
Gases are described by four variables:
Amount of gas (n)
Volume (V)
Pressure (P)
Temperature (T)
Kinetic theory – all particles are in constant motion …one exception

4. Kinetic Molecular Theory
Particles have insignificant volume
Large distance between particles
No attractive or repulsive forces
Motion is rapid and random
Travel in straight line path until collisions
Collisions are completely elastic
KE is transferred without loss

5. Temperature When heating a gas, most energy goes into motion
Average KE is related to temperature (K)
All particles same average KE at room temp
All motion stops at absolute zero
0 K or -273⁰C

6. Temperature Conversions
Celsius to Kelvin:
K = ⁰C
Kelvin to Celsius:
⁰C = K - 273

7. Ex: Convert 924.8 K to Celsius.

8. Ex: The hottest planet in the solar system measured a temperature of 480 K on a certain day. What is this temperature in Celsius?

9. Ex: The Rhinovirus reproduces especially well at nostril temperatures of 32.8⁰C. What is this temperature in Kelvin?

10. Gas Pressure Force exerted by gas per unit surface area
Result of billions of simultaneous collisions
Ex: Helium balloon
Vacuum – No pressure
no gas particles
Barometer – device used to measure atmospheric pressure

13. Pressure Conversions Standard Temperature and Pressure (STP)
0⁰C = 273 K
1 atm
1 atm = 760 mm Hg = 760 torr = kPa (SI)
These are conversion factors

14. Ex: Convert 25.3 atm to mm Hg.

15. Ex: The air pressure for a certain tire is 109 kPa
Ex: The air pressure for a certain tire is 109 kPa. What is this pressure in atmospheres?

16. Ex: The weather news gives the atmospheric pressure as 1. 07 atm
Ex: The weather news gives the atmospheric pressure as 1.07 atm. What is this atmospheric pressure in mm Hg?

17. Practice
An experiment at Sandia National Labs in New Mexico is performed at torr. What is this pressure in atm?
A bag of potato chips is sealed in a factory near sea level. The atmospheric pressure at the factory is mm Hg. The pressure inside the bag is the same. What is the pressure inside the bag of potato chips in kPa?

18. Practice Solutions
Answer: atm
Answer: 1.01 kPa

19. The Empirical Gas Laws There are four empirical gas laws
These laws relate the gas variables
Empirical – based on observation

20. Boyle’s Law Relates Pressure and Volume Law: P1 V1 = P2 V2
Inverse relationship
If V then P

23. Ex: If the volume of the lungs is 2
Ex: If the volume of the lungs is L during exhalation and the pressure is KPa, and the pressure during inhalation is KPa, what is the volume of the lungs during inhalation? 

24. Charles’s Law Relates Temp and Volume Law: Direct relationship
If T then V

26. Ex: If the volume of a gas at 25⁰C is 25
Ex: If the volume of a gas at 25⁰C is 25.5 L, what is the temperature when the volume is 75.0 L?

27. Gay-Lussac’s Law Relates Pressure and Temp Law: Direct relationship
If T then P

29. Ex: If the pressure of a gas at 75⁰C is 12
Ex: If the pressure of a gas at 75⁰C is 12.5atm, what is the temperature when the pressure is 3.75 atm?

30. Combined Gas Law
Combination of the previous empirical laws

31. Avogadro’s Law Relates Moles and Volume Law: Direct relationship
If n then V

32. Ex: If the moles of gas is 3
Ex: If the moles of gas is 3.75 mol N2 is used to inflate a balloon to 0.250L, what is the volume when the moles of gas are tripled?

33. The Empirical Laws
The previous laws are useful when only two variables are changing…everything else is constant.
They are laws for specific scenarios.
It is possible to use the laws to create a law that is general in nature – not specific.

34. Ideal Gas Law Combines the previous observations.
One of the most fundamental and important laws in chemistry.
Describes a SINGLE gas.
PRESSURE
TEMPERATURE
MOLES
VOLUME
GAS CONSTANT

35. Ideal Gases This is for ideal gases…not real gases.
Many real gases behave as ideal gases.
An ideal gas completely follows all the tenants of the Kinetic Molecular Theory.

36. atm∙L mol∙K Gas Constant – R This is a universal constant.
It is important to memorize the value of this number with the CORRECT units.
The value changes based on the units.
R =
atm∙L
mol∙K

37. Implications of R on PV=nRT
Previous laws – we could use any units as long as we were consistent.
The units used in the ideal gas law are determined by our choice of R.
If R = atm∙L/mol∙K is used:
P must be in atm
V must be in L
T must be in K

38. Tips on Solving Gas Law Problems
Write down all the variables that are known.
Determine which variable you are looking for.
Convert all variables to the correct units.
Write down the correct law/equation.
Rearrange equation.
Plug in values and solve.
See if your answer makes sense.

39. Ex: The gas in a spray can has a pressure of 103 kPa at 25 ⁰C
Ex: The gas in a spray can has a pressure of 103 kPa at 25 ⁰C. The can is heated to 928 ⁰C. What is the resulting pressure?

40. Ex: A balloon has a volume of 30. 0L at 313K and a pressure of 1147
Ex: A balloon has a volume of 30.0L at 313K and a pressure of mmHg. What is the volume at 0 ⁰C and 1 atm?

41. Ex: The temperature of a gas is 300. K and the volume is 821 L
Ex: The temperature of a gas is 300.K and the volume is 821 L. The temperature of the gas is raised by 35.0 K. What is the new volume?

42. Ex: The volume of a sealed, rigid cylinder is 20. 0L
Ex: The volume of a sealed, rigid cylinder is 20.0L. The pressure in the cylinder is 985 torr at 31 ⁰C. What is the effect when the temperature is lowered to 3.1 ⁰C?

43. Ex: An isothermal system contains CO2 gas at 900 K with a pressure of 5.31 kPa. What is the volume of the gas?

44. Ex: At a pressure of 1. 00 atm, one mole of a gas is at 0⁰C
Ex: At a pressure of 1.00 atm, one mole of a gas is at 0⁰C. What volume does it occupy?

45. Ex: A container with a volume of 3000. mL holds 32. 0 g CH4 gas at 25
Ex: A container with a volume of mL holds 32.0 g CH4 gas at 25.0⁰C. What is the pressure within the container?

46. Ex: In a 3. 05L bottle, CO2 gas is heated to 298K at a pressure of 225
Ex: In a 3.05L bottle, CO2 gas is heated to 298K at a pressure of kPa. How many grams of carbon dioxide gas are in the bottle?