UNIT 7: The Gas Laws. Mrs. Howland Chemistry 10 Rev. April 2016

Transcription

1 UNIT 7: The Gas Laws ì Mrs. Howland Chemistry 10 Rev. April 2016

2 ì Learners will be able to ì ì ì ì ì ì ì ì ì ì ì ì ì ì ì Unit 7: Gas Laws Describe atmospheric pressure and explain how a barometer works Describe Dalton s Law of ParGal Pressures Determine pargal pressure of gases from data List properges of gases DifferenGate among the behavior of pargcles in solids, liquids, and gases Explain the effects of temperature, pressure, and volume changes on the behavior of gas pargcles Define kinegc energy in terms of velocity and mass of pargcles Relate molecular mogon to temperature and molecular collisions to pressure Define standard temperature and pressure IdenGfy and convert between units of temperature and pressure Define molar volume State the wripen and mathemagcal expression of two gas laws, Boyle s Law and Charles Law Provide detailed real-life or laboratory examples of Boyle s Law and Charles Law Use the Common Gas Law to solve problems involving temperature, pressure, and volume Use the Ideal Gas Law to solve problems involving temperature, pressure, and volume for gases without affect by intermolecular forces.

3 Why are gases important?

4 Particle Theory of Matter ì ALL MATTER is made up of Gny pargcles (ATOMS) that are constantly moving ì 3 MAIN STATES OF MATTER: ì Solid ì Liquid ì Gas ì (plasma)

5 3 States of Matter ~ Defined

6 3 States of Matter ~ Particle Movement ~ ì ParGcles move at different speeds in each state of maper ì Increased energy (o]en in form of heat) will increase movement of pargcles

7 Properties of Gases ì No fixed shape; no fixed volume ì Lots of empty space between pargcles ì High kinegc energy ì Expand to fit the size of their container ì ParGcles diffuse to spread out evenly in container ì Easily compressed ì Weak apracgons

8 Kinetic Molecular Theory of Gases ì ParGcles in constant, random mogon ì Move in straight line ungl collisions with other pargcles or side of container ì ParGcles much smaller than space between pargcles (most gas volume is empty space and therefore negligible)

9 Kinetic Molecular Theory of Gases ì No forces of apracgon between pargcles or pargcles and container ì Collisions are elasgc (energy is not lost) ì Average kinegc energy depends on temperature

10 Measurable Properties ì Temperature ì Pressure ì Volume ì Amount (moles)

11 Defining Measurable Properties ì Temperature = Measurement of heat or how fast the pargcles are moving ì Pressure = Force per unit area (exerted by gas pargcles collisions with walls of container) ì Amount = Moles (amount of pargcles), abbreviated n ì MOLE: Amount of chemical substance; amount of any substance (atoms, molecules, ions) as there are atoms in 12g of carbon-12 (isotope of carbon) à We will be doing more with the mole in a later unit! ì Volume = Three-dimensional space inside the container holding the gas. ~ How much space does the gas take up?

12 ì ì ì Units of Temperature F (Fahrenheit) C (Celsius) K (Kelvin) à We will ALWAYS use KELVIN for gas laws!! To convert between Celsius and Kelvin:

13 Converting Units of Temperature ì Celsius to Kelvin: K = C ì Fahrenheit to Celsius: C = (F - 32) * 5/9 ì Remember! We will always use KELVIN for gas laws!

14 Comparing Units of Temperature

15 Units of Pressure ì atm = atmosphere ì mmhg = millimeters of mercury ì Torr = another name for mmhg J ì Pa = Pascal and kpa = kilopascal

16 Converting Between Units of Pressure

17 Converting Between Units of Pressure ì How? See the example below: Pressure is measured as mm Hg. What is this pressure in atm? mm Hg x 1 atm = 0.99 atm 760 mm Hg

18 Converting Between Units of Pressure ~ 1) 1820 mmhg =? atm YOU TRY IT! 2) 6.2 atm =? torr 3) 1159 torr =? mmhg

19 Measuring Pressure ì Torricelli Barometer = Instrument that uses mercury (Hg) to measure atmospheric pressure ì (like liquid in a drinking straw!) ì Pressure of Hg pushes down ungl it balances the force of atmosphere (pushes up)

20 Measuring Pressure ì Aneroid barometer uses a cell with small amount of air, lever, and pointer ì Face of instrument gives pressure measurement ì Pressure inside cell raises or lowers lever, which moves the dial VIDEO: hpps://goo.gl/gu9rxc

21 Dalton s Law of Partial Pressure ì Dalton s Law of ParXal Pressure States that the total pressure in a MIXTURE of gases is the SUM of the pargal pressure of each gas

22 Dalton s Law ~ YOU TRY IT! ì A container holds three gases: oxygen, carbon dioxide, and helium. A container holds 3 gases. The pargal pressures of the two gases are 2.00 atm, and 4.00 atm. The total pressure inside the container is atm. ì What is the parxal pressure of the third gas?

23 Changing the Properties what happens? ì In gases, the measureable properges have relagonships among each other ì Some properges (variables) will change other properges (variables) ì For example, THINK ABOUT IT what happens if you bring a helium balloon outside in the winter? VIDEO: hpps://goo.gl/exlihl

24 A given amount of gas (moles) can EXPAND or CONTRACT Same # of gas atoms! This means the moles of gas remains constant

25 Relationship between Pressure & Volume: Boyle s Law ì Charles Boyle studied the relationship between pressure, p, and volume, V, in the mid-1600s ì Boyle determined that for the same amount of a gas at constant temperature, there is an inverse relationship between volume and pressure: à when one INCREASES, the other DECREASES volume pressure

26 BOYLE S LAW Demonstration

27 Relationship between Temperature and Volume: Charles Law ì Jacques Charles studied the relationship volume, V, and temperature, T, around the turn of the 19 th century ì DIRECT RELATIONSHIP between V and T ì With the same amount of gas, as the volume INCRASES the temperature also INCREASES. ì If the temperature decreases than the volume also decreases. temperature volume

28 CHARLES LAW Demonstration

29 Relationship between Temperature and Pressure: Gay-Lussac s Law ì Joseph Gay-Lussac studied the temperature, T, and pressure, P, in the early 19 th century ì DIRECT RELATIONSHIP between P and T ì With the same amount of gas and CONSTANT VOLUME, as the temperature INCRASES, the pressure also INCREASES ì If the temperature decreases than the volume also decreases. temperature Pressure

30 How Gay-Lussac s Law is supported: ì With increasing temperature, pargcles move faster (increased kinegc energy) ì Faster movement results in more collisions with wall of container, increasing the pressure MUST HAVE CONSTANT VOLUME!!

31 Using MATH to PREDICT Behavior of Gases: Boyle s Law ì When temperature and moles are constant, we can use the formula to solve for one of the variables V or P

32 Using MATH to PREDICT Behavior of Gases: Boyle s Law ì When temperature and moles are constant, we can use the formula to solve for one of the variables V or P BEFORE AFTER These formulas are used to PREDICT or DETERMINE how gases have changed.

33 Using MATH to PREDICT Behavior of Gases: Charles Law ì When pressure and moles are constant, we can use the formula to solve for one of the variables V or T CROSS-MULTIPLY to solve, OR

34 Using MATH to PREDICT Behavior of Gases: Gay-Lussac s Law ì When and moles and volume are constant, we can use the formula to solve for one of the variables P or T

35 Avogadro s Hypothesis Equal volumes of gases at the same T and P have the same number of molecules. V and n are directly related ( n represents moles!) twice as many molecules

36 Avogadro s Hypothesis ì What happens to the number of pargcles when you blow up a balloon (add more air to the inside of a balloon)?

37 Let s play Which GAS LAW????

38 Combined Gas Law ì You don t HAVE to remember all 3 laws to do gas law problems! (yayyy!! J) ì All are related, so they can be combined in a SINGLE FORMULA: REMEMBER: T is in Kelvin!!

39 Combined Gas Law ì Cover up the variable that is CONSTANT and you automagcally get the gas law you need! REMEMBER: T is in Kelvin!! Need help? Try this video: hpps://goo.gl/6lysie

40 STANDARD CONDITIONS ì Occasionally, you will come across a problem that states standard temperature and pressure, or STP ì What does this mean?

41 Moles of Gas at STP ì What about MOLES? ì At STP, there are 22.4 L of gas and 1 mole of pargcles

42 Ideal Gas Law ì The ideal gas law is a way for sciengsts to predict the behavior/condigons of a gas without having to account for other intermolecular forces that affect gas behavior ì ASSUMES: ì ì ParGcles have no forces acgng among them (NO intermolecular forces) ParGcles themselves DO NOT take up space (the volume of the atoms and molecules is ignored)

43 Ideal Gas Equation ì PV = nrt ì P = pressure ì V = volume ì n = number of moles of gas ì R = universal gas law constant ì T = temperature

44 Universal Gas Law Constant ì The value used depends on the OTHER UNITS used in the equagon!

45 Solving problems using Ideal Gas Equation ì As with the other equagons, this equagon must be rearranged to solve for the unknown:

46 Real-World Application ì How do hot air balloons work? ì ì ì Which gas law do they employ? What is the typical volume of a hot air balloon? At what temperature does the air in the balloon need to reach in order to raise up?