1. Properties, Measuring, Calculations, The Gas Laws

2.  Gases are fluids  “Any substance that can flow”  Gases have a MUCH lower densities than liquids and solids  Enables them to “float” away  Gas particles are much farther apart

3.  What was density again?  If gases are much less dense, do you think they will frequently run into each other or seldom come into contact?

4.  Gas particles can be smooshed together compressed  Think of a syringe or a soda bottle  Gases fill the container completely, spread out.  Collisions of gas molecules are what causes pressure. The more collisions, the higher the pressure  Gas molecules in the atm collide with Earth’s surface, creating atmospheric pressure.

5.  Pressure is “force divided by area”  You need to know the force and area over which the force is being exerted.  SI units for force is the newton, N  One newton is the force that gives an acceleration of 1 m/s 2 to an object whose mass is 1 kg.  The SI unit of pressure is the pascal, Pa  The force one newton over an area of one square meter.

6. UnitAbbreviationEquivalent of pascals Atmosphereatm1 atm = 101.325 Pa Barbar1 bar = 100.025 Pa Millimeter of Hgmm Hg1 mm Hg = 133.322 Pa PascalPa1 Pounds per sq. in.psi1 psi = 6.89286x10 3 Pa Torrtorr1 torr = 133.322 Pa One mmHg is also equal to 1 torr 1 atm = 760 torr = 760 mmHg

7.  Standard Temperature and Pressure, STP  273.15 K (0ºC), 1 atm  Makes it easier to work with gases when they are at constant temperatures and pressure.

8.  The KMT – a model that is used to predict gas behavior.  States that gas molecules are in constant rapid, random motion.  Spaces between are VERY large compared to the sizes of the gas particles  Explains the fluidity and compressibility

9.  Pressure = P = pressure exerted by the gas  Temperature = T = temperature in Kelvins of the gas  Volume = V = total volume occupied by the gas  Number of moles = n = number of moles of gas

10.  We know how to calculate this when given the mass and the identity of the compound  Converting using the molar mass (mol/g)  No different for gases  How about if we are given the concentration?  Molarity is a measurement of “how much is in solution”  Solute = what is being dissolved  Solvent = what is doing the dissolving  Solution = the entire mixture, both solute and solvent Molarity (M) = mol solute / L solution

11.  We can determine the number of moles using the concentration and volume, then stick it into one of the following gas laws. Keep this in mind  Practice: How many moles are in 10 mL of a 3 M HCl soln?  What is the concentration of 25 mL of H 2 SO 4 when 0.089 moles were added?

12.  Robert Boyle found that as pressure of a gas increases in a closed container, the volume of the gas decreases.  The product of the pressure and volume (PV) remain constant as long as temperature remains the same.  The inverse relationship between pressure and volume became known as Boyle’s Law PV (at any point) = k, so: P 1 V 1 = P 2 V 2

13.  A sample of oxygen gas has a volume of 5.8 mL at a pressure of 0.947 atm. What will the volume of the gas be at a pressure of 1.000 atm if the temperature remains constant?  A sample of gas in a syringe has a volume of 9.66 mL at a pressure of 64.4 kPa. The plunger is depressed until the pressure is 94.6 kPa. What is the new volume, assuming constant temp.?

14.  Heating a gas makes it expand, cooling it makes it contract  We can relate these two if the pressure remains constant  This direct relationship between temperature and volume is known as Charles’s Law V/T (at any point) = k, so: (V 1 /T 1 ) = (V 2 /T 2 )

15.  A balloon is inflated to 665 mL volume at 27ºC. It is immersed in a dry-ice bath at -78.5ºC. What is its volume, assuming the pressure remains constant?

16.  Temperature-Pressure Relationships  As you increase the pressure, the temperature increases. As the pressure decreases, the temperature decreases.  This direct relationship between temperature and pressure is known as Gay-Lussac’s Law. **Pressure of a gas is proportional to its absolute temp** P/T = k (at any point), so: (P 1 /T 1 ) = (P 2 /T 2 )

17.  An aerosol can containing gas at 101 kPa and 22ºC is heated to 55ºC. Calculate the pressure of the heated can.

18.  We can set these equations equal to a common variable and then set them equal to one another  By doing this, we can derive a COMBINED GAS LAW P 1 V 1 = P 2 V 2 T 1 T 2  This equation enables us to make calculations consisting of varying pressures, temperatures, and volume (holding nothing but the number of moles constant).

19.  A soda bottle has a volume of 1.50 L at 25ºC at standard pressure (1.00 atm). The bottle is then taken to the bottom of the ocean to a temp of 1.00ºC and a pressure of 0.67 atm. What will the new volume of this bottle be?

20.  Avogadro!!  States at the same temperature and pressure, balloons of the same volume with contain the SAME number of moles of gas, REGARDLESS of the gasses identity.  H 2, O 2, CO 2, it does not matter!!  1 mole of gas = 22.41 L. The mass of a gas at 0ºC and 1 atm (STP) is equal to the gas’s molecular (molar) mass V = kn, where k is the proportionality constant

21.  No gas perfectly obeys all four of these laws under all conditions  These assumptions work well for most gases and most conditions  One way to model a gas’s behavior is to assume that the gas is an ideal gas that perfectly follows these laws  Does not condense to a liquid at low temps  Does not have forces or attraction or repulsion between the particles  And is composed of particles that have no volume

22. P V = n R T P = Pressure V = Volume n = number of moles of gas R = Universal gas constant 8.314 L*kPa*mol -1 *K -1 or0.0821 L*atm*mol -1 *K -1 T = Temperature of gas

23.  How many moles of gas are in 22.41 Liters at 101.325 kPa and 0ºC?

24.  A real gas deviates from the ideal gas behavior at low temperature and high pressure  The volume of the particles themselves is close to the total volume, so the actual volume will be higher than calculated.  So, with regards to the Ideal Gas Law, low temperature and high pressure is BAD!!  Condensation and particle attractions as they get closer Remember This!!!

25.  Diffusion – the movement of particles from regions of higher density to regions of lower density.  Odor of ammonia smelling up the room  Involves an increase in entropy (measure of randomness)  Effusion – the passage of a gas under pressure through a tiny opening  Like out of a leaking tire

26.  This law states that the volumes of gases involved in a chemical change can be represented by the ratio of small whole numbers ___ H + ___ Cl  ___ HCl  This tells us our 7 diatomics ARE, in fact, diatomic

27.  Dalton showed that in a mixture of gases, each gas exerts a certain pressure as if it were alone with no other gases mixed with it  The pressure of each gas in a mixture is call the Partial Pressure  This is known as Dalton’s Law of Partial Pressures  Total pressure = sum of the pressures of all the components within it P total = P A + P B + P C + … + P n

28.  The gauge pressure in a tire is 28 psi, which adds to atmospheric pressure of 14.0 psi. What is the internal tire pressure in kPa?  A gas sample has a volume of 125 mL at 91.0 kPa. What will its volume be at 101 kPa?

29.  A gas at 65ºC occupies 4.22 L. At what Celsius temperature will the volume be 3.87 Liters, at the same pressure?  A scientist warms 26 mL of gas at 0.0ºC until its volume is 32 mL. What is its new temperature in Kelvin?

30.  A sample of hydrogen exerts a pressure of 0.329 atm at 47ºC. What will the pressure be at 77ºC, assuming constant volume?  A cylinder of gas at 55 kPa and 22ºC is heated until the pressure is 655 kPa. What is the new temperature??

31.  A balloon has a volume of 1.25 liters and a temperature of 20ºC. The pressure when filled was 1.05 atm. The balloon was released and allowed to float away, reaching 1.87 kilometers where the pressure is 0.667 atm and a temperature of -10 0 C, what would the new volume of the balloon be?

32.  How many moles of argon are there in 20.0 L, at 25ºC and 101 kPa?  How many moles of air are in 1.00 L at -23ºC and 101 kPa?  A weather balloon is inflated with 12.0 g of He at -23ºC and 100.0 kPa. What is its volume?

33.  An unknown gas effuses at a speed one- quarter of that of He. What is the molar mass of the unknown gas? It is either sulfur dioxide of sulfur trioxide. Which gas is it?

34.  A mixture of CO 2, CO, H 2, and N 2 are floating around in a reagent bottle. The pressure of the system is 0.25 atm. The pressures of the gases are 0.002 atm, 0.058 atm, 0.084 atm, and unknown, respectively. Calculate the pressure of the N 2 component.

35.  Worksheet attached to your notes, front and back