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The Gas Laws. Pressure Force per unit area. Gas molecules fill container. Molecules move around and hit sides. Collisions are the force. Container has.

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Presentation on theme: "The Gas Laws. Pressure Force per unit area. Gas molecules fill container. Molecules move around and hit sides. Collisions are the force. Container has."— Presentation transcript:

1 The Gas Laws

2 Pressure Force per unit area. Gas molecules fill container. Molecules move around and hit sides. Collisions are the force. Container has the area. Measured with a barometer.

3 Barometer The pressure of the atmosphere at sea level will hold a column of mercury 760 mm Hg. 1 atm = 760 mm Hg 1 atm Pressure 760 mm Hg Vacuum

4 Units of pressure 1 atmosphere = 760 mm Hg 1 mm Hg = 1 torr 1 atm = 101,235 Pascals = kPa Can make conversion factors from these.

5 What is 724 mm Hg in torr? torr torr torr 4.73,359 torr

6 What is 724 mm Hg in kPa? kPa kPa kPa 4.73,359 kPa

7 What is 724 mm Hg in atm? atm atm atm 4.73,359 atm

8 The Gas Laws Boyles Law Pressure and volume are inversely related at constant temperature. PV= k As one goes up, the other goes down. P 1 V 1 = P 2 V 2 Graphically

9 V P (at constant T)

10 V 1/P (at constant T) Slope = k

11 Examples 20.5 L of nitrogen at 25ºC and 742 torr are compressed to 9.8 atm at constant T. What is the new volume? L L L

12 30.6 mL of carbon dioxide at 740 torr is expanded at constant temperature to 750 mL. What is the final pressure in kPa? kPa kPa kPa kPa

13 Charles' Law Volume of a gas varies directly with the absolute temperature at constant pressure. V = kT (if T is in Kelvin) V 1 = V 2 T 1 = T 2 Graphically

14 V (L) T (ºC) He H2OH2O CH 4 H2H ºC

15 Examples What would the final volume be if 247 mL of gas at 22ºC is heated to 98ºC, if the pressure is held constant? mL mL mL

16 At what temperature would 40.5 L of gas at 23.4ºC have a volume of 81.0 L at constant pressure? K C K

17 Avogadro's Law At constant temperature and pressure, the volume of gas is directly related to the number of moles. V = k n (n is the number of moles) V 1 = V 2 n 1 = n 2

18 Gay- Lussac Law At constant volume, pressure and absolute temperature are directly related. P = k T P 1 = P 2 T 1 = T 2

19 Combined Gas Law If the moles of gas remains constant, use this formula and cancel out the other things that dont change. P 1 V 1 = P 2 V 2. T 1 T 2

20 Ideal Gas Law PV = nRT V = L at 1 atm, 0ºC, n = 1 mole, what is R? R is the ideal gas constant. R = L atm/ mol K Tells you about a gas is NOW. The other laws tell you about a gas when it changes.

21 Ideal Gas Law A hypothetical substance - the ideal gas Think of it as a limit. Gases only approach ideal behavior at low pressure (< 1 atm) and high temperature. Use the laws anyway, unless told to do otherwise. They give good estimates.

22 Example A 47.3 L container containing 1.62 mol of He is heated until the pressure reaches 1.85 atm. What is the temperature? K K K

23 Gas Density and Molar Mass D = mass/Volume Let MMstand for molar mass MM = mass/n n= PV/RT PV = mass RT MM

24 Example What is the density of ammonia at 23ºC and 735 torr? g/L g/L g/L

25 Gases and Stoichiometry Reactions happen in moles At Standard Temperature and Pressure (STP, 0ºC and 1 atm) 1 mole of gas occupies L. If not at STP, use the ideal gas law to calculate moles of reactant or volume of product.


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