1. Temperature and Pressure
Gay Lussac’s Law
Temperature and Pressure
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

2. Gay-Lussac’s Law: P and T
In Gay-Lussac’s Law
the pressure exerted by a gas is directly related to the Kelvin temperature.
V and n are constant.
P1 = P2
T1 T2

3. Learning Check Solve Gay-Lussac’s Law for P2. P1 = P2 T1 T2
Multiply both sides by T2 and cancel
P1 x T2 = P2 x T2
T T2
P2 = P1 x T2 T1

4. Calculation with Gay-Lussac’s Law
A gas has a pressure at 2.0 atm at 18°C. What
is the new pressure when the temperature is
62°C? (V and n constant)
1. Set up a data table;
Conditions 1 Conditions 2
P1 = 2.0 atm P2 =
T1 = 18°C T2 = 62°C + 273
= 291 K = K ?

5. Calculation with Gay-Lussac’s Law (continued)
2. Solve Gay-Lussac’s Law for P2:
P1 = P2
T T2
P2 = P1 x T2 T1
P2 = 2.0 atm x 335 K = atm
291 K
Temperature ratio
increases pressure

6. Try it A gas has a pressure of 645 torr at 128°C. What is the
temperature in Celsius if the pressure increases to
1.50 atm (n and V remain constant)?
1. Set up a data table:
Conditions Conditions 2
P1 = 645 torr P2 = 1.50 atm x 760 torr = 1140 torr
1 atm
T1 = 128°C T2 = K – 273 = ?°C
= 401 K

7. Solution 2. Solve Gay-Lussac’s Law for T2: P1 = P2 T1 T2 T2 = T1 x P2
T2 = 401 K x torr = K = 436°C
645 torr Pressure ratio
increases temperature

8. Avogadro’s Law

9. Avogadro's Law: Volume and Moles
In Avogadro’s Law
the volume of a gas is directly related to the number of moles (n) of gas.
T and P are constant.
V1 = V2
n n2

10. Learning Check
If 0.75 mole helium gas occupies a volume of 1.5 L, what volume will 1.2 moles helium occupy at the same temperature and pressure?
1) L
2) 1.8 L
3) 2.4 L

11. Solution STEP 1 Conditions 1 Conditions 2 V1 = 1.5 L V2 = ???
n1 = mole He n2 = 1.2 moles He
STEP 2 Solve for unknown V2
V2 = V1 x n2 n1
STEP 3 Substitute values and solve for V2.
V2 = 1.5 L x moles He = 2.4 L
0.75 mole He

12. Partial Pressure (Dalton’s Law)

13. Partial Pressure The partial pressure of a gas
is the pressure of each gas in a mixture.
is the pressure that gas would exert if it were by itself in the container.

14. Dalton’s Law of Partial Pressures
Dalton’s Law of Partial Pressures indicates that
pressure depends on the total number of gas particles, not on the types of particles.
the total pressure exerted by gases in a mixture is the sum of the partial pressures of those gases.
PT = P1 + P2 + P

15. Dalton’s Law of Partial Pressures

16. Illustrating Partial Pressures

17. Total Pressure Gas mixtures
For example, at STP, one mole of a pure gas in a volume of 22.4 L will exert the same pressure as one mole of a gas mixture in 22.4 L.
V = 22.4 L
Gas mixtures
1.0 mole N2
0.4 mole O2
0.6 mole He
1.0 mole
0.5 mole O2
0.3 mole He
0.2 mole Ar
1.0 mole
1.0 atm
1.0 atm
1.0 atm

18. Scuba Diving
When a scuba diver dives, the increased pressure causes N2(g) to dissolve in the blood.
If a diver rises too fast, the dissolved N2 will form bubbles in the blood, a dangerous and painful condition called "the bends".
Helium, which does not dissolve in the blood, is mixed with O2 to prepare breathing mixtures for deep descents.

19. Learning Check
A scuba tank contains O2 with a pressure of atm and He at 855 mm Hg. What is the total pressure in mm Hg in the tank?

20. Solution 1. Convert the pressure in atm to mm Hg
0.450 atm x 760 mm Hg = 342 mm Hg = P(O2) atm
2. Calculate the sum of the partial pressures.
Ptotal = P(O2) + P(He)
Ptotal = 342 mm Hg mm Hg
= 1197 mm Hg

21. Learning Check
For a deep dive, a scuba diver uses a mixture of helium and oxygen with a pressure of atm. If the oxygen has a partial pressure of 1280 mm Hg, what is the partial pressure of the helium?
1) 520 mm Hg
2) mm Hg
3) mm Hg

22. Solution PTotal = 8.00 atm x 760 mm Hg = 6080 mm Hg 1 atm
PTotal = PO PHe 2
PHe = PTotal - PO2
PHe = mm Hg mm Hg
= mm Hg

23. Gases We Breathe The air we breathe is a gas mixture.
contains mostly N2 and O2 and small amounts of other gases.
TABLE 6.4

24. Learning Check
A.If the atmospheric pressure today is 745 mm Hg, what is the partial pressure (mm Hg) of O2 in the air?
1) ) ) 760
B. At an atmospheric pressure of 714, what is the partial pressure (mm Hg) N2 in the air?
1) ) )

25. Blood Gases
In the lungs, O2 enters the blood, while CO2 from the blood is released.
In the tissues, O2 enters the cells, which release CO2 into the blood.

26. Partial Pressures in Blood and Tissue
Blood Gases
In the body,
O2 flows into the tissues because the partial pressure of O2 is higher in arterial blood, and lower in the tissues.
CO2 flows out of the tissues because the partial pressure of CO2 is higher in the tissues, and lower in the blood.
Partial Pressures in Blood and Tissue
Oxygenated Deoxygenated
(arterial) (venous)
Gas Blood Blood Tissues
O or less
CO or greater

27. Gas Exchange During Breathing
TABLE 6.5