Chemistry 20 Chapter 3 PowerPoint presentation by R. Schultz

Preparation Density: Worksheet BLM 3.0.1

Preparation

3.1 Gases and Kinetic Molecular Theory Gases take shape of their container and completely fill it. Liquids …… Properties: compressible expand as temp  at constant pressure low viscosity low density completely miscible with each other macroscopic properties

3.1 Gases and Kinetic Molecular Theory Gas technologies: pneumatics SCUBA hot air balloons

3.1 Gases and Kinetic Molecular Theory Gases defined theoretically using concept of an “ideal gas” ideal gases don’t really exist but gas theories based on gases being ideal  an ideal gas has molecules that: - are point masses (they have no size) - collide with walls and each other, with perfect elastic collisions (no attraction between molecules or molecules and wall)

3.1 Gases and Kinetic Molecular Theory ideal gases never condense; no matter how low the temp or how high the pressure Which real gas is most ideal? Why? He smallest “molecules” and weakest “intermolecular” attractions (LDF: 2 eˉ) helium boils at -269ºC  4 degrees above absolute zero hydrogen is almost as ideal, boiling at -253ºC

3.1 Gases and Kinetic Molecular Theory Under room temperature/pressure conditions most real gases are very close to ideal When are real gases least ideal? low temperature and high pressure no need to memorize this – Why? just think about conditions most likely to make a gas condense

3.1 Gases and Kinetic Molecular Theory Gas particles are in constant random motion sample of ideal gas particles random path of a single ideal gas particle fig 3.3, page 100 the higher the temperature, the higher the average E k of the particles

3.1 Gases and Kinetic Molecular Theory Do 3.1 Review, page 101 – questions 1, 3, 5, 7, 8, 9

3.2 Gases and Pressure Pressure is force per unit area Galileo and water pumps – recall from Science 10? figure 3.4, page 102 = N area = 1 m 2

3.2 Gases and Pressure

Mercury barometer - Toricelli figure 3.6, page 103 sealed end open end petri dish: half-filled with Hg glass tube completely filled with Hg cover open end and insert into dish; remove cover a similar device made with water would have a height ??? times as tall? vacuum 13.6 times: 10.3 m

3.2 Gases and Pressure Standard atmospheric pressure = 760 mmHg Pressure Units: 1 atm = 760 mmHg = Pa = kPa = bar page 104 – I will give this to you on all tests and quizzes related to gases Torr psi "Hg pressure demos* according to the kinetic molecular theory, pressure is due to? collisions of gas particles with walls of container Other pressure units: discuss *egg, pop bottle, can

3.2 Gases and Pressure pressure unit conversion examples: use conversion box from page 104 Example 2 b page 112 is still the key 850 mmHg = ? kPa Try 2 a, c and 3, page atm = 760 mmHg = Pa = kPa = bar

3.2 Gases and Pressure Do worksheet BLM questions 1 and 2 only

3.2 Gases and Pressure The relationship between pressure and volume for a fixed quantity of gas at constant temperature Pressure can be varied by adding weights to plate on top of syringe plunger Volume can be read by reading scale on syringe diagram page 106

3.2 Gases and Pressure Here are some data from a similar experiment – weights have been converted to pressures for you Can you find a mathematical relationship between P and V? Example: Try, do it for each line – does it give a near constant value? P (kPa)V (mL) No. Try something else

3.2 Gases and Pressure Answer: This is Boyle’s Law P (kPa)V (mL) x x 10 3

3.2 Gases and Pressure Statements of Boyle’s Law: Volume of a gas is inversely proportional to (varies inversely as) applied pressure Mathematically: and You should know Boyle’s Law in these ways but you won’t use it to calculate – it will be part of other formulas (at constant temperature) Fig 3.11A page 109

3.2 Gases and Pressure Kinetic Molecular Theory and Boyle’s Law Pressure due to collision of particles with walls of container As volume , more collisions with walls →  pressure

3.3 Gases and Temperature Read page 113 Discover relationship – like before T (ºC)V (L) Nothing simple works

3.3 Gases and Temperature Problem: Zero on Celsius (and Fahrenheit) temp scales is not really zero! Need to change temperature to absolute temperature in Kelvins (where 0 is 0!) t (ºC)V (L) T (K)

3.3 Gases and Temperature Absolute (Kelvin) temperature scale based upon 0 being absolute zero, ( ºC) To change from Celsius to Kelvins, add if t = temp (ºC) and T = temp (K), Do questions 7 and 8, page 119 – add or subtract , but round to correct # of significant digits

3.3 Gases and Temperature Statements of Charles’ Law: Volume is directly proportional to (or varies directly as) absolute temperature *T(K) As with Boyle’s Law, you will do no direct calculations with Charles’ Law – you will use as part of a more complete law

3.3 Gases and Temperature Finding Absolute Zero Experiment

3.3 Gases and Temperature Kinetic molecular theory and Charles’ Law: As temp , particles gain kinetic energy and travel faster – they would therefore exert greater pressure on the walls of the container If walls of the container are flexible or movable they will expand to make P inside = P outside

Theories and Laws Theories and Laws: What’s the difference? Law A statement about observations that seems to be true. Theory An explanation, often at the atomic level, to explain why laws work Example: Boyle’s Law:Example: Kinetic Molecular Theory – explains why Boyle’s Law works

3.2 Gases and Pressure Kinetic Molecular Theory and Boyle’s Law Pressure due to collision of particles with walls of container As volume , more collisions with walls →  pressure

3.3 Gases and Temperature