Outline General properties of gas Kinetic molecular theory of gas Development of the ideal gas law Ideal gas law PV=nRT Conclusion exercise
States of matter Discussion : what we have already known about the gas?
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
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 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
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).
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
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 101.325 kPa (kilopascal) 760 mm Hg 760 torr 1 bar 1 atm 14.7 psi
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 = 0.625 atm 760 mm Hg 760 mm Hg 29.4 psi x = 1.52 x 103 mm Hg 14.7 psi
Standard Temperature & Pressure 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
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
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.
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. 1 2 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.
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 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)
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? 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.
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)
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?