1. Important Definitions for Gas Laws Unit

2. Temperature
Measure of the average kinetic energy of the particles in a substance
What is kinetic energy?
Heat - the transfer of energy from one substance to another due to temperature differences
Goes from _____________energy to _____________ energy

3. Volume
The amount of space occupied by a sample or substance

4. Pressure
Force divided by area
A “push”  what we will use

5. What is a gas? Gas – no definite shape or volume
It will take shape of container it is contained in
Gases have 3 properties we can measure:
Temperature
Volume
Pressure

6. Let’s Learn the Gas Laws

7. What are the 3 properties of gases?
Temperature (T)
Volume (V)
Pressure (P)
Remember, if you keep any 1 of these constant, there is a known relationship between the others

8. Three Gas Laws
Charles Law
Gay-Lussac’s Law
Boyles Law

9. Volume and Temperature
Charles Law
Volume and Temperature

10. Charles Law The relationship between volume and temperature
Pressure is constant

11. Temperature vs. Volume Graph5 10 15 20 25 30
Volume (mL)
Temperature (C)
100
– 273

12. Absolute Zero
If a volume vs. temperature graph is plotted for gases, most lines can be extrapolated downward so that when volume is 0 the temperature is -273 C.
Obviously naturally, gases don’t really reach a 0 volume, but the spaces between molecules approach 0.
At this point all molecular movement stops.
–273C is known as “absolute zero” (0 K)
no KE- energy of motion
Therefore we get the Kelvin scale…

13. Kelvin Scale
Lord Kelvin suggested that a reasonable temperature scale should start at a true zero value.
He kept the convenient units of C, but started at absolute zero.
Therefore since at 0 volume, temperature is -273 C:
K = C
Practice: 62C = ? K
From now on, we will be using Kelvin!!

14. Back to Charles's Law… Your data shows that…
As T increases, V increases
As T decreases, V decreases
Therefore this is a direct relationship

15. But why is this important??

16. My experience with a hot air balloon
The balloon and basket were placed in a field.
The burner was ignited and a huge fan blew the heated air into the balloon on the ground.
The balloon started to fill up and lift off of the ground.
When the balloon was completely filled with hot air where would it be??????

17. History behind Charles's Law
In the early 1800's in France hot air balloons were extremely popular.
Scientists were eager to improve the performance of their balloons.
We know that no extra air was added to the balloon  so how did heating the air (gas) make it rise?

18. Jacques Charles
He discovered that the volume of the gas will increase as the temperature increases
Conversely he stated that a decrease in temperature results in a decrease in volume
So ↑T = ↑V
↓T = ↓V
In a hot air balloon, what is happening to the T? V?

19. A balloon and liquid nitrogen
What is happening to the balloon?
What is happening to the temperature? Volume?

20. Lets try some calculations
Always set up: V1 = T1 = V2 = T2 =
You will have one unknown
Write down the starting temperature or volume…
What is the relationship?
If you want a bigger number
If you want a smaller number

21. Joseph Louis Gay-Lussac. Pressure and Temperature

22. Lets look at \data…
Pressure
Temp

23. Gay-Lussac’s work
Determined the relationship between temperature and pressure of a gas.
Measured the temperature of air at different pressures, and observed a pattern of behavior which led to his mathematical law.
During his experiments volume of the system and amount of gas were held constant.
He found: ↑T = ↑P
↓T = ↓P
Therefore this is a direct relationship.

24. REVIEW: What is pressure?
The pressure of a gas is the push exerted on the wall of the container a gas is trapped in.
There are several units for pressure depending on the instrument used to measure it including:
Atmosphere (atm)
Millimeters of mercury (mmHg)
Kilopascals (kPa)
Torr (torr)
You need to be able to convert between any of these if you are given the conversion factors…

25. Why is this applicable?? Did you ever look on the back of cake mix?
There are special instructions for high altitude
At high altitudes, pressure is lower because there is less air above you (less push)
So how will we have to adjust the temperature?
Examples
High Altitude ( ft): For all pans, heat oven to 325°F.

26. Another example…
Car tires… what happens to the pressure inside the tire during the winter (when it is cold)?
As temperature decreases, pressure decreases
This is why we have to add air to the tires during winter

27. Lets try some calculations
Always set up: P1 = T1 = P2 = T2 =
** Remember temperature has to be in K and pressure in atm **
You will have one unknown
Write down the starting temperature or pressure…
What is the relationship?
If you want a bigger number
If you want a smaller number

28. Robert Boyle Volume and Pressure

29. Lets look at data…

30. Boyle’s Law
Boyle’s law states that pressure and the volume of a gas are inversely proportional.
At constant temperature for a fixed mass.
Therefore: ↑V = ↓ P
↓V = ↑ P
Therefore this is a indirect relationship.

31. Why is this important? Let’s try making straw snap…
Hold both ends and flick it…
What happened?
Now reduce the volume and flick it…

32. Okay, but what else? Making the best water balloons…
What happens if you keep filling the balloon?
What is the best water balloon for a water balloon toss?
Smaller – will not pop as easily
What is the best water balloon to throw at someone?
Larger – will pop very easily

33. Lets try some calculations
Always set up: V1 = P1 = V2 = P2 =
** Remember pressure in atm **
You will have one unknown
Write down the starting volume or pressure…
What is the relationship?
If you want a bigger number
If you want a smaller number