1. Investigating Gases
Gas Laws

2. Working with a syringe
Start with the plunger all the way into the syringe. Try pulling out and pushing in the plunger. Now “plug the end” with your finger and try to pull and push the plunger
Record on your paper what you notice about each situation.
Step 1) no air
Unplugged
Plugged with finger
Push plunger in
Pull plunger out

3. Repeat but this time plug the opening with your finger first.
Now pull out the plunger so there is some air in the syringe. Try pushing in the plunger and pulling out the plunger.
Repeat but this time plug the opening with your finger first.
Step 2) Air
Unplugged
Plugged with finger
Push plunger in
Pull plunger out

4. Now Let’s add a marshmallow
Take two marshmallows and draw a face on each
Remove the plunger from the syringe
Place one marshmallow in the syringe and replace the plunger
Push in the plunger to force out as much air as possible without squeezing the marshmallow

5. cont’d Plug the syringe with your finger
Pull on the plunger, hold it in the “out” position and record your observations
Predict what will happen when you release the plunger. Record
Release the plunger and record your observations
Repeat several times so everyone gets a chance to “play”

6. Why did the marshmallow behave this way?

7. You just learned boyle’s law
Boyle’s law states that volume of a gas varies INVERSELY with pressure at constant temperature and constant number of gas molecules.
If pressure decreases (pull plunger out) = volume increases (marshmallow got bigger)
If pressure increases (push plunger in) = volume decreases (marshmallow got smaller)

8. Rules for gases When discussing gases, one must always specify the
Temperature
Volume
Pressure
Quantity (number of molecules)
All of these will affect the way the gases behave.

9. Boyle’s Law
P1V1 = P2V2
Temperature is constant and number of gas molecules stays the same
Pressure and Volume are inversely related

10. Charles’s Law
V1 = V2
T T2
Pressure is constant and number of gas molecules stays the same
Temperature and Volume are directly related
Temperature is in KELVINS
K = Celsius + 273

11. Gay-Lussac’s Law
P1 = P2
T T2
Volume is constant and number of gas molecules stays the same
Temperature and Pressure are directly related
Temperature is in KELVINS
K = Celsius + 273

12. P1 V1 = P2V2 T1 T2 Number of gas molecules stays the same
Combined Gas Law
P1 V1 = P2V2
T T2
Number of gas molecules stays the same
Temperature is in KELVINS
K = Celsius + 273

13. Homework:
p419 #8
p421 #10
p423 #12
p425 #15-22

14. Quick Quiz
Imagine a marshmallow sealed on Earth in a steel container at 1 atm pressure. Predict what change (if any) would occur in the volume of the marshmallow if the container were opened in each of the following situations (assuming not temperature change):
1. In a space shuttle: weightless but pressurized at 1 atm
2. On a space walk: weightless with 0 atm pressure
3. On a deep-sea dive: at a depth of 1000 ft which 4 atm of pressure