1. Chemistry 141 Wednesday, October 10, 2017 Lecture 16 The Gas Laws
Chemistry 11 - Lecture 11
9/30/2009
Chemistry 141
Wednesday, October 10, 2017
Lecture 16
The Gas Laws

3. Introduction to gases Why learn about gases?
They are important in chemistry and to the existence of life!
Teach us about the physics of molecules and ensembles of molecules

4. Pressure
An open-ended tube of mercury up-ended in a dish of mercury does not spill out
Why not?
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5. Atmospheric pressure
What is the pressure exerted by the atmosphere on the surface of the earth?
m = mass of atmosphere = 5×1018 kg
g = acceleration due to gravity = 9.81 m/s
A = surface area of Earth = 5×1014 m2

6. Units of Pressure
The pressure exerted by the atmosphere at sea level is:
height of barometer mercury column

7. How much is an atmosphere?
Otto von Guericke's vacuum sphere couldn't be separated by the teams of horses (1654).

8. Measuring pressure: the manometer
Allows evaluation of the pressure of a trapped gas compared to that of the atmosphere.
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9. Measuring pressure: the manometer
In both of the examples shown below, the height of the mercury column is 18 mm. What is the pressure of the trapped gas in each case? (Assume atmospheric pressure of 760 mmHg or 1 atm.) a atm b. 709 mmHg c. 778 mmHg d. 18 mmHg e. 742 mmHg f atm
Case 1
Case 2
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10. Boyle’s experiments
What happens when mercury is added to the open end of the J tube?
Pressure of trapped gas increases
Volume of trapped gas decreases
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11. Boyle’s measurements (ml) (inHg) (inHg) 48 0.00 29.13 1398
Volume Hg height Ptotal =Patm + PHg PV
(ml) (inHg) (inHg) -4
+2.81
+3.38
roughly constant -4
+23.69
Need to add more and more Hg to get the same change in volume
It gets harder and harder to compress the gas

12. The volume of a gas is inversely proportional to its pressure
Boyle’s Law
Volume decreases
Pressure increases
The volume of a gas is inversely proportional to its pressure
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13. Using gas laws
5.00 L of krypton at STP is compressed at constant temperature until a final volume of 2.30 L is reached. What is the final gas pressure?

14. Concept Question
What will happen to the volume of an inflated balloon when it is placed in liquid nitrogen (77 K)?
goes up
goes down
stays constant

15. Charles’s Law
The volume of a gas is proportional to its temperature
decrease in T
decrease in V
V = bT + C
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16. Absolute Temperature
V = bT + C
V = bT
We can define a new scale of temperature such that the zero of temperature is the point where the gases have zero volume. This temperature is called absolute zero.
Absolute zero = °C T(K) = T(°C)
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17. Avogadro’s Hypothesis
Gay-Lussac noted that the volumes of gases at same T and P that react together are in the ratio of small whole numbers
Avogadro concluded that equal volumes of gases contain equal numbers of particles (at same T and P)
The volume a gas occupies is proportional to the number of particles
n = # of particles in 1 volume
a = a constant
V = an
2V = a(2n)

18. Combining the gas laws Boyle’s Law: Charles’s Law: Avogadro’s Law:
combine constants into R
The ideal gas law