1. Combined Gas Law

2. Combined Gas Law
If you list all three gas laws side by side, what do you notice?
P1 x V1 = P2 x V2 V1 = V2 P1 = P2
T1 = T2 T1 = T2
List what you notice in your notes, we will compare in a moment.

3. Combined Gas Law
Because of these similarities, all of those relationships can be combined into something called the Combined Gas Law.
Who do you suppose that was named for?
What does not change in the combined gas law?
The Combined Gas Law allows you to do calculations in which only the amount of gas is constant.

4. P1 x V1 = P2 x V2 T1 T2 Combined Gas Law
Initial Volume
Final Volume
Initial Pressure
Final Pressure
P1 x V1 = P2 x V2
T T2
Notice what happens when you eliminate any of the variables…
Initial Temperature
Final Temperature

5. Combined Gas Law – with constant temperature = Boyle’s Law
P1 x V1 = P2 x V2
T T2

6. Combined Gas Law – with constant pressure = Charles’s Law
P1 x V1 = P2 x V2
T T2

7. Combined Gas Law – with constant volume = Gay-Lussac’s Law
P1 x V1 = P2 x V2
T T2

8. Example
The volume of a gas-filled balloon is 30.0L at 313K and 153kPa of pressure. What would the volume be at standard temperature and pressure (STP)?
Remember that Standard Temperature is 0°C = 273K and Standard Pressure is 1atm = 101.3kPa.

9. The volume of a gas-filled balloon is 30
The volume of a gas-filled balloon is 30.0L at 313K and 153kPa of pressure. What would the volume be at standard temperature and pressure (STP)?
First, identify your variables:
P1 =
V1 =
T1 =
P2 =
V2 =
T2 =
153 kPa
30.0 L
313 K
Standard Pressure is kPa
?? What we are looking for
Standard Temperature is 273 K

10. Then, plug in your numbers and solve
P1 x V1 = P2 x V2
T T2
153kPa x 30.0L = 101.3kPa x V2
313K K
After some algebra…
V2 = 39.5 L

11. Does this make sense?
What effect would you expect a decrease in pressure to have? A decrease in temperature?
If nothing else changed, a decrease in pressure would accompany an increase in volume.
If nothing else changed, a decrease in temperature would accompany a decrease in volume.
They are both happening…so the result is a mix of the two  ends up being a slight increase in volume.