1. #1. Gas is composed of particles- usually molecules or atoms
The Nature of Gases
Three basic assumptions of the kinetic theory as it applies to gases:
#1. Gas is composed of particles- usually molecules or atoms
Small, hard spheres
Insignificant volume; relatively far apart from each other
No attraction or repulsion between particles

2. #2. Particles in a gas move rapidly in constant random motion
Move in straight paths, changing direction only when colliding with one another or other objects
Average speed of O2 in air at 20 oC is an amazing 1700 km/h!
Random walk is a very short distance

3. #3. Collisions are perfectly elastic- meaning kinetic energy is transferred without loss from one particle to another- the total kinetic energy remains constant

4. Gas Pressure – defined as the force exerted by a gas per unit surface area of an object
Due to: a) force of collisions, and b) number of collisions
No particles present? Then there cannot be any collisions, and thus no pressure – called a vacuum

5. Atmospheric pressure results from the collisions of air molecules with objects
Decreases as you climb a mountain because the air layer thins out as elevation increases

6. The SI unit of pressure is the pascal (Pa)
At sea level, atmospheric pressure is about kilopascals (kPa)
Older units of pressure include millimeters of mercury (mm Hg), and atmospheres (atm) – both of which came from using a mercury barometer
Equal pressures:1 atm = 760 mm Hg = kPa

7. This is called Standard Temperature and Pressure, or STP
For gases, it is important to relate measured values to standards
Standard values are defined as a temperature of 0 oC and a pressure of kPa, or 1 atm
This is called Standard Temperature and Pressure, or STP

8. Section 13.1 The Nature of Gases
What happens when a substance is heated? Particles absorb energy!
Some of the energy is stored within the particles- this is potential energy, and does not raise the temperature
Remaining energy speeds up the particles (increases average kinetic energy)- thus increases temperature

9. The particles in any collection have a wide range of kinetic energies, from very low to very high- but most are somewhere in the middle, thus the term average kinetic energy is used
The higher the temperature, the wider the range of kinetic energies

10. The boiling point (bp) is the temperature at which the vapor pressure of the liquid is just equal to the external pressure on the liquid
Bubbles form throughout the liquid, rise to the surface, and escape into the air

11. Since the boiling point is where the vapor pressure equals external pressure, the bp changes if the external pressure changes
Normal boiling point- defined as the bp of a liquid at a pressure of kPa (or standard pressure)

12. Section 13.2 The Nature of Liquids
Normal bp of water = 100 oC
However, in Denver = 95 oC, since Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kPa (Recipe adjustments?)
In pressure cookers, which reduce cooking time, water boils above 100 oC due to the increased pressure

13. - Page 394
Not Boiling
Normal Boiling kPa = 100 oC
Boiling, 34 kPa = 70 oC

14. Variables that describe a Gas
The four variables and their common units:
1. pressure (P) in kilopascals
2. volume (V) in Liters
3. temperature (T) in Kelvin
4. amount (n) in moles
The amount of gas, volume, and temperature are factors that affect gas pressure.

15. The Gas Laws are mathematical
The gas laws will describe HOW gases behave.
Gas behavior can be predicted by the theory.
The amount of change can be calculated with mathematical equations.
You need to know both of these: the theory, and the math

16. Boyle's Law: This law defines the relationship between pressure and volume if temperature and amount of gas is held constant. If the volume of a container is increased, the pressure decreases. If the volume of a container is decreased, the pressure increases. The law is described by the following equation: P1V1 = P2V2

17. Boyle's Law: Example: A sample of gas is in a 2
Boyle's Law: Example: A sample of gas is in a 2.00 L contain at a pressure of mmHg. What is the new pressure of the sample if the container’s volume is reduced to 1.25 L?
Answer: This problem is solved by inserting values into the given equation:
(740.0 mmHg) (2.00 L) =(X) (1.25 L)
Solving for X will give you a new pressure of 1184 mmHg.

18. Charles's Law: This law defines the relationship between volume and temperature if pressure and amount of particles are held constant. If the temperature of a gas is increased, the volume of the gas will increase. If the temperature of a gas is decreased, the volume of the gas will decrease. This is a direct relationship. One goes down, so does the other.

19. Charles's Law: Picture the gas particles flying around inside a balloon. If you were to put the balloon in the freezer, the gas particles would slow down, therefore they would not hit the balloon walls as hard and the balloon would shrink in size.
V1/T1 = V2/T2 or V1T2 = V2T1

20. Example: A gas is collected and found to fill 2. 85 L at 25. 0°C
Example: A gas is collected and found to fill 2.85 L at 25.0°C. What will be its volume at standard temperature?
Answer: Convert 25.0°C to Kelvin and you get 298 K. Standard temperature is 273 K. We plug into our equation like this:
Solving for the new volume gives a value of 2.61 liters. The volume has decreased as the temperature has decrease.

21. Gay-Lussac's Law:
This law characterizes the relationship between pressure and temperature when volume and amount are held constant. If the temperature of a container is increased, the pressure increases. If the temperature of a container is decreased, the pressure decreases. This is another example of a direct relationship. One goes up, so does the other.

22. Think about this law in this manner, if the gas particles are moving faster, as happens when the temperature of a gas is increased, the force of the impact will increase. Therefore, increasing the temperature will increase the pressure exerted by a gas.

23. Example: 10. 0 L of a gas is found to exert 97. 0 kPa at 25. 0°C
Example: 10.0 L of a gas is found to exert 97.0 kPa at 25.0°C. What would be the required temperature to change the pressure to standard pressure?
Answer: Change 25.0°C to K and remember that standard pressure in kPa is Insert values into the equation and get: K

24. Avogadro's Law:
This law gives the relationship between volume and number of gas particles when pressure and temperature are held constant. Remember the number is measured in moles. If the amount of gas in a container is increased, the volume increases. If the amount of gas in a container is decreased, the volume decreases. Another direct relationship.

25. The volume of a container holding a gas will increase with increasing numbers of gas particles because there are more particles impacting the wall of the container.
Example: A 5.00 L sample of a gas is known to contain mol. If the amount of gas in this container is increased to 1.80 mol, what new volume will result (at an unchanged temperature and pressure)?

26. PV = nRT: The Ideal Gas Law:
The derivation of this law is a lot of math. So, I will just give you the equation and examples of how to use it.
PV = nRT
The Numerical Value for R: L atm / mol K
Notice the weird unit on R. Say out loud "liter atmospheres per mole Kelvin." This is not the only value of R that can exist. It depends on which units you select.

27. Example: A sample of gas with a mass of 2
Example: A sample of gas with a mass of grams is found to occupy a volume of L at 22.0°C at a pressure of atm. How many moles of the gas are present?
( atm) (2.850 L) = (n) ( L atm / mol K) (295.0 K)
and solve for n = mol