3. Outline General properties of gas Kinetic molecular theory of gas
Development of the ideal gas law
Ideal gas law
PV=nRT
Conclusion
exercise

4. States of matter
Discussion : what we have already known about the gas?

5. General properties of gas
Gases can be compressed.(0.1%)
lots of empty space
Gases undergo diffusion & effusion.
random motion
gases form a homogeneous mixture
differ from liquid and solid

6. Kinetic molecular theory of gas 气体分子动理论
Particles in an ideal gas…
have no volume.
have elastic collisions.
are in constant, random, straight-line motion.
don’t attract or repel each other.
have an avg. KE directly related to Kelvin temperature

7. Ideal gas & Real gas Particles in an Ideal gas(理想气体)
the gas particles have no volume
no intermolecular forces
Particles in a Real gas（真实气体）
have their own volume
attract each other(intermolecular forces)
Gas behavior is most ideal…
at low pressures
at high temperatures
in nonpolar atoms/molecules

8. Physical quantities to describe a sample of gas.
Volume V (liter)
Pressure P (pascal)
Temperature T (kelvins)
Mole of the gas n (mole)
Tires
Gas laws : The relationship among the four variables (V, P, T, n).

9. Temperature T
Always use absolute temperature (Kelvin) (绝对温度)when working with gases.
Temperature is a numerical measure of hot or cold and is related to the average kinetic energy of moving particles.
absolute zero（绝对零度）, represents zero kinetic energy. ºC K
-273
100
273
373

10. Pressure P Definition: force that acts on a given area
units of pressure
pascal (SI, Pa)
millimeters of Hg (mm Hg)
torr
bar
Atmospheres
psi
kPa (kilopascal)
760 mm Hg
760 torr
1 bar
1 atm
14.7 psi

11. Pressure Conversions 1 atm1 a 475 mm Hg x = 0.625 atm 29.4 psi x
1. What is 475 mm Hg expressed in atm?
1 atm1 a
2. The pressure of a tire is measured as 29.4 psi.
What is this pressure in mm Hg?
1 atm
475 mm Hg x
= atm
760 mm Hg
760 mm Hg
29.4 psi x
= 1.52 x 103 mm Hg
14.7 psi

12. Standard Temperature & Pressure
STP(标准状况)
At STP, any gas will have a volume of 22.4L.
Standard Temperature & Pressure
0°C K
1 atm kPa

13. Ideal gas law Gay-Lussac’s law Charles’s law Avogadro’s principle
Boyle’s law
Charles’s law
Gay-Lussac’s law
Avogadro’s principle

14. Boyle's Law: P &V (n,T held constant)
Pressure
Volume
P ∝ 1/V
PV = constant
Pressure is inversely proportional to volume when temperature is held constant.

15. Exercise 1
A gas is at 10 L and 700 mm Hg. (a) What is the pressure at 20L(temperature held const)? (b) State the behavior of the gas during the change.
P1 × V1 = P2 × V2
The volume increases, the frequency at which the gas molecules
strike the walls decrease. Pressure is proportional to the frequency
with which the molecules strike the container.

16. Charles’s law: V & T, (n,P held constant)
The volume of a gas is directly proportional to temperature.
(n,P = constant)
Temperature MUST be in KELVINS!

17. Charles’s law (B) Exercise 2
Considering Charles’s law, the gas will have ----if the volume is reduced? ( )
(A) decreased pressure (B) decrease temperature
(C) increase temperature (D) increase the moles of gas
(B)

18. Gay-Lussac’s law: P&T (n,V held constant)
Temperature MUST be in KELVINS!

19. Avogadro's Law: V&n (T,P held constant)
T, P = constant

20. Ideal gas law
Attention to the unit of the variables.

21. Where does R come from? Attention to the unit of the variables.
Units of R
Value
L atm mol-1 K-1
0.0821
J mol-1 K-1
8.314
L mm Hg mol-1 K-1
6.24× 104
Attention to the unit of the variables.

22. conclusion Ideal gas law PV = nRT (ideal gas)
Boyle‘s Law P ∝ 1/V (n, T)
Charles’s law V ∝ T (n, P)
Gay-Lussac’s law P ∝ T (n, V)
Avogadro‘s Law V ∝ n
Ideal gas law PV = nRT (ideal gas)

23. Practice makes perfect
1 The kinetic molecular theory is used to explain the behavior of gas, Briefly describe the theory. Write the Ideal Gas Law.
(Free-Response)
2 A gas occupies 250ml, and its pressure is 550mm Hg at 25℃.
(a) If the gas is expanded to 450 mL, what is the pressure of the gas now?
(b) What temperature is needed to increase the pressure of the gas to exactly 1 atm, 250mL?
(c)How many of the gas are in the sample?