2The Nature of GasesGases have some interesting characteristics that have fascinated scientists for 300 years.The first gas to be studied was air & it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas.
3The Nature of GasesBut this realization did not make the study of gas behavior more difficult.Although air is a mixture of several different gases, it behaves much the same as any single gas.Regardless of their chemical identity, gases tend to exhibit similar physical behaviors
4The Nature of GasesGas particles can be monatomic (Ne), diatomic (N2), or polyatomic (CH4) – but they all have these characteristics in common:1) Gases have mass.2) Gases are compressible.3) Gases fill their containers.4) Gases diffuse5) Gases exert pressure.6) Pressure is dependent on Temp.
5Kinetic Molecular Theory There is a theory that modern day chemist’s use to explain the behaviors and characteristics of gases - the Kinetic Molecular Theory of Matter.The word kinetic refers to motion.The word molecular refers to molecules
6Kinetic Molecular Theory The theory states that the tiny particles in all forms of matter are in constant motion.This theory is used to explain the behaviors common among gasesThere are 3 basic assumptions(ideas) of the KMT as it applies to gases.
7KMT Assumption #1 A gas is composed of small hard particles. The particles have an insignificant volume and are relatively far apart from one another.There is empty space between particles.No attractive or repulsive forces between particles.
8KMT Assumption #2The particles in a gas move in constant random motion.Particles move in straight paths and are completely independent of each otherParticles path is only changed by colliding with another particle or the sides of its container.
9KMT Assumption #3All collisions a gas particle undergoes are perfectly elastic.No energy is lost from one particle to another, and the total kinetic energy remains constant.
10Gases have mass.Gases seem to be weightless, but they are classified as matter, which means they have mass.The density of a gas – the mass per unit of volume – is much less than the density of a liquid or solid, however.
12Gases “R” squeezableIf you squeeze a gas, its volume can be reduced considerablyA gases low density allows for there to be a lot of empty space between gas molecules.
13This empty space can be compressed simply by adding pressure. We can use this ability of a gas to do work for us.Think of shocks on a car.You really are riding on a pillow of air.A bump in the road compresses the gas in the shocks until the bump’s energy is absorbed.
14Gases fill their containers Gases expand until they take up as much room as they possibly can.Gases spread out to fill containers until the concentration of gases is uniform throughout the entire space.
16Gases exert pressureGas particles exert pressure by colliding with objects in their path.The sum of all of the collisions makes up the pressure the gas exerts.
17Pressure depends on Temp The higher the temperature of a gas -the higher the pressure that the gas exertsThe reverse of that is true as well, as the temperature of a gas decreases – the pressure decreases.
20Gas variablesIn order to describe a gas sample completely and then make predictions about its behavior under changed conditions, it is important to deal with the values of:1) amount of gas2) volume3) temperature4) pressure
21Gas LawsStudies of the behavior of gases played a major role in the development of physical sciences in the 7th and 8th centuries.The Kinetic Molecular theory marked a significant achievement in understanding the behavior of gases.Observations have become mathematical laws which we can use to predict outcomes.
22Boyle’s LawRobert Boyle was among the first to note the relationship between pressure and volume of a gas.He measured the volume of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments Temperature and amount of gas weren’t allowed to change
24How does Pressure and Volume of gases relate graphically? PV = kTemperature,# of particlesremain constantPressure
25Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume at 4 atm? Boyle’s Mathematical Law:What if we had a change in conditions?since PV = kP1V1 = P2V2Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume at 4 atm?
26Charles’s LawJacques Charles determined the relationship between temperature and volume of a gas.He measured the volume of air at different temperatures, and observed a pattern of behavior which led to his mathematical law.During his experiments pressure of the system and amount of gas were held constant.
27Volume of balloon at room temperature Volume of balloon at 5°C
28How does Temperature and Volume of gases relate graphically? V/T = kPressure,# of particlesremain constantTemp
29V1 V2 = T1 T2 Charles’s Mathematical Law: What if we had a change in conditions?since V/T = kV1 V2T T2=Eg: A gas has a volume of 3.0 L at 127°C. What is its volume at 227 °C?
30Gay Lussac’s LawOld man Lussac determined the relationship between temperature and pressure of a gas.He measured the temperature of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments volume of the system and amount of gas were held constant.
31Think of a tire... Car before a trip Pressure Gauge Let’s get on the roadDude!
32Think of a tire...Car after a long tripPressureGaugeWHEW!
33How does Pressure and Temperature of gases relate graphically? P/T = kVolume,# of particlesremain constantTemp
34P1 P2 = T1 T2 Lussac’s Mathematical Law: What if we had a change in conditions?since P/T = kP P2T T2=Eg: A gas has a pressure of 3.0 atm at 127º C. What is its pressure at 227º C?
35Boyle’s P V T Charles’ V T P Gay-Lussac’s P T V SummaryLAWRELAT-IONSHIPCON-STANTBoyle’sP VP1V1 = P2V2TCharles’V TV1/T1 = V2/T2PGay-Lussac’sP TP1/T1 = P2/T2V