Chemistry 6A F2007. Dr. J.A. Mack. Reaction Yields: 10/24/07. % Yield = g 0.427g

Transcription

1 Chemistry 6A F007 Dr. J.A. Mack Reaction Yields: he quantities of products calculated from balanced chemical equations represent the maximum yield of product that can be fmed accding to the reaction stoichiometry. his maximum cresponds to 00 % yield. It is known as the theetical yield. How many grams of ammonia fm from the complete reaction of 0.35g of nitrogen with excess hydrogen? N (g) + 3 H (g) NH 3 (g) How many grams of ammonia fm from the complete reaction of 0.35g of nitrogen with excess hydrogen? 0.35g N N (g) + 3 H (g) NH 3 (g) mol N molnh 3 8.0g N mol N 7.04g NH 0.47g NH 3 3 molnh3 What is the % yield of the reaction if only 0.3g of NH 3 fm? his lesser amount is called the Actual Experimental Yield. he percent yield is given by the following equation: % Yield From the previous slide: Experimental Yield heetical Yield % Yield 0.3 g 0.47g % 3 4

2 Chapter 6: he States of Matter SAES OF MAER LEARNING OBJECIES: After completing this chapter, you should be able to: SOLIDS have rigid shape, fixed volume.. Wk with density calculations.. Explain the states of matter using the kinetic molecular they. 3. Use the idea gas laws to determine the effects of temperature, pressure, volume and moles based on changes. 4. Understand the concepts of partial pressure, diffusion, and effusion. 5. Calculate energy changes f heating, cooling, change of state f a substances. Solids Liquids External shape can reflect the atomic and molecular arrangement. LIQUIDS have no fixed shape and may not fill a container completely. GASES expand to fill their container. 5 6 CHARACERISIC PROPERIES OF HE HREE SAES OF MAER Gases 8 9

3 Kinetic hey (K) of Gases: Clausius (857) Postulates: A gas is a collection of a very large number of particles that remains in constant random motion. he pressure exerted by a gas is due to collisions with the container walls he particles are much smaller than the distance between them. Kinetic hey (K) of Gases: Clausius (857) he particles move in straight lines between collisions with other particles and between collisions with the container walls. (i.e. the particles do not exert fces on one another between collisions.) he average kinetic energy (½ mv ) of a collection of gas particles is proptional to its Kelvin temperature. Gas particles collide with the walls of their container and one another without a loss of energy. 0 Units of Energy Energy: is the capacity to do wk, supply heat. Energy Wk + Heat Conservation of Energy Energy cannot be created destroyed; It can only be converted from one fm to another. SI Unit f energy is the joule abbreviated J kg m s J Another unit of energy is the calie cal 4.84 J (exactly) A nutritional Calie: Cal 000 cal kcal conversion fact 4.84 J (exactly) cal all potential some potential & kinetic all kinetic 4

4 me mass here same pressure at all Pressure at the Molecular Level When a pressure differential exists, mass moves from the area of high pressure to an area of low pressure. When there is no differential, mass does not move. (a) Gas particles are in constant random motion. (b) Pressure is the sum total fce of all of the individual collisions between the gas particle and the container walls. 5 6 Pressure Measurement Units: he Barometer A barometer is a device that measures pressure in terms of the height of a column of liquid. P atm When an open tube is placed in the Hg, the pressure inside equals the pressure outside. Atmospheric pressure no mass movement 760 tr atm 760 mm Hg tr mm Hg 7 When an evacuated tube is inverted and placed in a reservoir of the liquid, the pressure difference between the atmosphere and the evacuated tube fces the liquid upwards. 9

5 A tire has a pressure of 3.0 psi (pounds per square inch) What is the pressure in atm and mm Hg? 3.0 psi 3.0 psi atm 4.7psi atm 4.7psi.8 atm 760mm Hg 650mm Hg atm Gas: emperature Scales F gas calculations, we need an absolute scale, one that does not take on negative values. he conversion between o C and degrees K is: K o C When perfming calculations with absolute temperatures, on must use the Kelvin scale. Convert 5.0 o C to Kelvin: Convert 33 K to o C: 5.0 o C K 33 K o C Watch your sig. figs.!!!! Standard emperature and Pressure: Often it is the case that scientists need a reference point at which they can compare gas systems. his reference point refers to a standard temperature and pressure (SP) SP atm 760 tr 760 mm Hg & 0 o C 73.5 K 3

6 Boyle s Law: Pressure vs. olume Charles s Law: olume vs. emperature (absolute) P P Constant Constant at constant pressure A plot of vs. yields a straight line P y mx + b /P 4 A plot of vs. yields a straight line y mx + b 5 Boyle s Law: Pressure vs. olume P P Constant as pressure increases, volume decreases! P P P P 6 if P P P P double the pressure, halve the volume Calculate the new volume of a 35 ml sample of helium at a 5.0 o C after the temperature is changed to 50.0 o C. () () () () () 35 ml ( )K ( )K () () Wrong! One must use the Kelvin scale! () () he temperature doubles so the volume doubles, Right? 38 ml 7

7 Charles s Law: olume vs. emperature (absolute) as temperature increases, volume increases! Constant 8 if Double the Kelvin temperature, double the volume! What temperature (in o C) would change the volume of 35. ml of helium at 5.0 o C to 575 µl? 575 µl ( )K L 35. ml 3 0 ml 6 0 µ L 30 L o C