1 Mr. ShieldsRegents Chemistry U05 L03

2 Properties of Gases (1)A gas has VOLUME AND MASS (2) The DENSITY of a gas is considerably LESS than either a solid or liquid either a solid or liquid (3) The density of a gas is affected by TEMPERATURE AND PRESSURE (4) A gas neither DEFINITE SHAPE NOR VOLUME Let’s go over the properties of gases again:

3 Properties of Gases (5) There is NO PERMANENT ATTRACTION between one gas molecule and the next one gas molecule and the next (6) Gases MOVE EASILY through one another to form homogeneous solutions form homogeneous solutions (7) Gases exert PRESSURE (8) Gas Pressure is affected by TEMPERATURE

4 Properties of Gases To understand why gases have these properties We need to understand something called This theory was developed by a number of scientists over a long period of time. KMT is used to explain the behavior of Gases as well as Liquids and solids. We will use it only in connection with gases. the Kinetic Molecular Theory. The KMT was developed to explain what happened on A molecular scale what earlier scientists observed On a macro scale. These macro observations lead to Several laws before KMT was established.

5 Early Scientists So, who were these earlier scientists? Robert Boyle (1627 – 1691) - Boyle’s law (1662) - Explains the Pressure-Volume relationship - PV=k

6 Early Scientists Jacques Charles (1746 – 1823) - Charle’s Law (1787) - Vol vs.Temp relationship - V/T = k Joseph Gay-Lussac (1778 – 1850) - Gay-Lussac’s Law (abt 1807) - Pressure vs. Temp relationship - P/T = k

7 Early Scientists John Dalton (1766 – 1844) - The same Dalton who proposed atoms exist - Law of Partial Pressures (abt. 1801) - P Total = Pgas1 + Pgas2 + Pgas3 + … Amedeo Avogadro (1776 – 1856) - The same Avogadro who proposed Equal vol. of gases contains equal nos. of molecules - Volume vs. no. of particles relationship - V/n = k

8 Thomas Graham (1805 – 1869) - Graham’s law of effusion (1846) - Rate of effusion is inversely proportional it’s molecular weight - Effgas1 = 1/(M gas1)1/2 These early scientists looked at the macro properties of gases. Do you know why this was a Topic? Hint: What “powered” the industrial revolution?

9 Power from steam This is one common example of the use Of power derived from steam

10 Development of KMT Daniel Bernoulli (1700 – 1782) Suggested that the pressure exerted by a gas on the walls of its container is the sum of the many collisions by individual molecules all moving independently of each other James Maxwell (1831 – 1879) 1866 – Determined that the Avg. velocity of molecules = (3RT/M) 1/2 M= Mol. mass, R= gas const, T= Temp(K)

11 Development of KMT Rudolph Clausius (1822 – 1888) Heat can never travel from cold to hot. It always travels from hot to cold Molecules move with speeds much faster than the magnitude of the bulk fluid (macro) velocity the magnitude of the bulk fluid (macro) velocity Introduces the concept of MEAN FREE PATH The mean distance a molecule travels before Collision with another molecule

12 Development of KMT Ludwig Boltzman (1844 – 1906) Maxwell-Boltzmann Theory Developed in conjunction with James Maxwell Molecules have a specific distribution of velocities at a given temp

13 Development of KMT We’ve looked at some of the historical developments behind the understanding of gas behavior. This understanding lead to the Kinetic Molecular Theory. We now need to discuss what typically are considered the 5 key assumptions of the KMT: 1.Gas particles do not attract or repel one another 2.The volume occupied by Gas particles is negligibly small compared to the overall volume small compared to the overall volume 3. Gas Particles are in constant random straight line motion 4. No KE is lost when gas molecules collide with each other 5. The avg. KE of all gases is directly proportional to Temp in Kelvin in Kelvin LEARN THESE!!