Properties of Gases and gas mixtures ppt

general properties of gases ppt and thermodynamic properties of gases ppt
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Dr.SamuelHunt,United Arab Emirates,Teacher
Published Date:21-07-2017
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Chapter 11 GasesProperties of Gases • Expand to completely fill their container = Compressible • Take the shape of their container. • Low density. Much less than solid or liquid state. • Mixtures of gases are always homogeneous • www.ThesisScientist.comThe Structure of a Gas • Gases are composed of particles that are flying around very fast in their container(s). • They move in straight lines until they encounter either the container wall or another particle, then they bounce off. • If you were able to take a snapshot of the particles in a gas, you would find that there is a lot of empty space in there. • It’s why balloons look round www.ThesisScientist.comKinetic Molecular Theory • The particles of the gas (either atoms or molecules) are constantly moving & The attraction between particles is negligible. • Therefore: When the moving particles hit another particle or the container, they do not stick, but they bounce off and continue moving in another direction.  Like billiard balls. www.ThesisScientist.comKinetic Molecular Theory of Gases • The average kinetic energy of the particles is directly proportional to the Kelvin temperature. As you raise the temperature of the gas, the average speed of the particles increases. But don’t be fooled into thinking all the particles are moving at the same speed www.ThesisScientist.comKinetic Molecular Theory www.ThesisScientist.comWhat does all this Pushing do? • Gas molecules are constantly in motion. • As they move and strike a surface, they push on that surface.  Push = force. • If we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exerting.  Pressure = force per unit area= pounds per square inch www.ThesisScientist.comThe Effect of Gas Pressure • The pressure exerted by a gas can cause some amazing and startling effects. www.ThesisScientist.comWhich Way Would Air Flow? Two filled balloons are connected with a long pipe. One of the balloons is plunged down into the water. Which way will the air flow? Will air flow from the lower balloon toward the top balloon; or will it flow from the top balloon to the bottom one? Tro' ww s In w tr .T odu hes citor sSc yi e C nh tiesm t.c is otm ry, Chapter 9 11Is This Possible at a Depth of 20 m = 65.6 ft? Tro' ww s In w tr .T odu hes citor sSc yi e C nh tiesm t.c is otm ry, Chapter 10 11Soda Straws and Gas Pressure The pressure of The pressure of the the air inside the air inside the straw straw is the same is lower than the as the pressure pressure of the air outside of the air outside the straw—so the straw—so liquid levels are liquid is pushed the same on both up the straw by sides. the outside air. www.ThesisScientist.comAir Pressure • The atmosphere exerts a pressure  At sea level it is 14.7 psi.  The atmosphere goes up about 370 miles, but 80% is in the first 10 miles from Earth’s surface. • This is the same pressure that a column of water would exert if it were about 10.3 m high. • Therefore water can not be pumped higher, in a straw for instance, than 10.3 m/33.8 ft www.ThesisScientist.comMeasuring Air Pressure • Use a barometer. • Column of mercury supported by air gravity pressure. • Force of the air on the surface of the mercury balanced by the pull of gravity on the column of mercury. www.ThesisScientist.comAtmospheric Pressure and Altitude • The higher up in the atmosphere you go, the lower the atmospheric pressure is around you. At the surface, the atmospheric pressure is 14.7 psi, but at 29,028 ft it is only 4.9 psi (1/3) • Rapid changes in atmospheric pressure may cause your ears to ―pop‖ due to an imbalance in pressure on either side of your ear drum. www.ThesisScientist.comPressure Imbalance in Ear If there is a difference in pressure across the eardrum membrane, the membrane will be pushed out—what we commonly call a ―popped eardrum.‖ www.ThesisScientist.comCommon Units of Pressure Unit Average air pressure at sea level Pascal (Pa) 101,325 Kilopascal (kPa) 101.325 Atmosphere (atm) 1 (exactly) Millimeters of mercury (mmHg) 760 (exactly) Inches of mercury (inHg) 29.92 Torr (torr) 760 (exactly) 2 Pounds per square inch (psi, lbs./in ) 14.7 www.ThesisScientist.comExample 11.1—A High-Performance Bicycle Tire Has a Pressure of 125 psi. What Is the Pressure in mmHg? Given: 125 psi Find: mmHg Solution Map: psi atm mmHg 1 atm 760 mmHg 14.7 psi 1 atm Relationships: 1 atm = 14.7 psi, 1 atm = 760 mmHg Solution: 1 atm 760 mmHg 3 125 psi 6.4610 mmHg 14.7 psi 1 atm Check: Since mmHg are smaller than psi, the answer makes sense. www.ThesisScientist.comBoyle’s Law • Pressure of a gas is inversely proportional to its volume. Constant T and amount of gas. Graph P vs. V is curved. Graph P vs. 1/V is in a straight line. • As P increases, V decreases by the same factor. • P x V = constant. • P x V = P x V . 1 1 2 2 www.ThesisScientist.comWhen you double the pressure on a gas, the volume is cut in half (as long as the temperature and amount of gas do not change). www.ThesisScientist.comGas Laws Explained— Boyle’s Law • Boyle’s law says that the volume of a gas is inversely proportional to the pressure. • Decreasing the volume forces the molecules into a smaller space. • More molecules will collide with the container at any one instant, increasing the pressure.

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