OutlineGeneral properties of gasKinetic molecular theory of gasDevelopment of the ideal gas lawIdeal gas law

PV=nRTConclusionexercise

States of matter

Discussion : what we have already known about the gas?

General properties of gasGases 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

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

Ideal gas & Real gasParticles 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 volumeattract each other(intermolecular forces)

Gas behavior is most ideal…at low pressuresat high temperaturesin nonpolar atoms/molecules

Physical quantities to describe a sample of gas.

Tires

Volume V (liter)Pressure P (pascal)Temperature T (kelvins)Mole of the gas n (mole)

Gas laws : The relationship among the four variables (V, P, T, n).

ºC

K-273 0 100

0 273 373

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.

Pressure P

area

forcepressure

units of pressurepascal (SI, Pa) millimeters of Hg (mm Hg)torrbarAtmospherespsi

101.325 kPa (kilopascal)760 mm Hg760 torr 1 bar1 atm 14.7 psi

Definition: force that acts on a given area

Pressure Conversions1. 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?

475 mm Hg x 1 atm

760 mm Hg= 0.625 atm

29.4 psi x760 mm Hg

14.7 psi = 1.52 x 103 mm Hg

STP(标准状况 )

At STP, any gas will have a volume of 22.4L.

Standard Temperature & Pressure

0°C 273 K

1 atm 101.325 kPa

Boyle's Law: P &V (n,T held constant)

PV = constant

Pressure is inversely proportional to volume when temperature is held constant.

Pressure

Volume

P ∝ 1/V

Exercise 1A 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

1 2

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.

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!

Charles’s lawExercise 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)

Gay-Lussac’s law: P&T (n,V held constant)

Temperature MUST be in KELVINS!

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

1 2

T, P = constant

Ideal gas law

Attention to the unit of the variables.

Where does R come from?

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.

conclusionBoyle‘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)

Practice makes perfect1 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?