Jan 29, 2016
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?