1 Gases The Gas Laws. 2 Properties of Gases n No fixed shape or volume n Molecules are very far apart and in a state of constant rapid motion n Can be.

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Presentation transcript:

1 Gases The Gas Laws

2 Properties of Gases n No fixed shape or volume n Molecules are very far apart and in a state of constant rapid motion n Can be compressed n There are weak attractive forces between molecules

3 Temperature n Measure of average velocity(speed) of molecules n 0 kelvins = C(absolute zero) all molecular motion stops at this temperature n __T kelvins = __ 0 C n C = _______K n 80 0 C = _______ K n 300 K = _______ 0 C

4 Pressure n Force per unit area. P=F/A N/m 2 n Gas molecules fill container. n Molecules move around and hit sides. n Collisions are the force. n Container has the area. n Measured with a barometer.

5 Gas Pressure n Measured in Pascal (Pa) or Kilopascals (KPa) n 1000 Pa = 1 KPa n 1 Pascal = 1N/m 2 n 1 standard atmosphere = 1 atm n 1atm = KPa = 760 mm Hg n 1 atm = 760 torr = KPa n 1 torr = 101.3/ 760 KPa

6 Standard Temperature and Pressure n When temperature is 0 0 C or 273 Kelvins, pressure is KPa – this is known as standard temperature and pressure or STP.

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

8 Manometer Gas h n Column of mercury to measure pressure. n h is how much lower the pressure is than outside.

9 Manometer n h is how much higher the gas pressure is than the atmosphere. h Gas

10 Ideal Gas Law n PV = nRT n P= pressure in KPa n V= volume in L n n= moles n R = constant 8.31 LxKPa/molxK n T = temperature in Kelvins.

11 Ideal Gas ( page 483) n A hypothetical substance - the ideal gas n Molecules are dimensionless n Molecules are in constant motion n Collisions are elastic (no energy lost) n No attractive forces in molecules n

12 Example n Example 1 – A sample of oxygen gas occupies 5.6 L at STP. How many grams of oxygen are present?

13 Example 2 n Calculate the pressure of 1.75 g of helium gas at C occupying n 3.25 L.

14 Answers to Worksheet n mol n g n L n 4. 90g n 5. 13L n mol x x10 4 n x10 2 mol K, C

15 Molar Volume of Gases n Equal volumes of all gases at equal temperature and pressure contain same number of particles.(Avogadro’s hypothesis) n Draw diagrams here n 1mole = 6.02 x particles of gas n The volume must be the same for all gases n Molar volume = volume occupied by 1 mole of gas

16 Molar Volume n Molar volume of any gas is 22.4L at STP 0 o C and 101.3KPa n Knowing the volume allows you to find the moles n Molar volume is 24.5L at NTP (normal temperature and pressure) 25 o C and 101.3KPa n At higher temperature the molar volume is expected to be higher.

17 Exception to molar volume n Some gases have molar volume slightly different than 22.4L because of attraction between molecules. n Examples are Cl 2 has molar volume of 22.1L and SO 2 = 21.9L at STP

18 Examples 1. What is the molar volume of any gas at STP? 2. What is the molar volume of a gas if moles occupy 8.30L? 3. What volume will 128 g of methane occupy at STP? 4. What volume will moles of CO 2 occupy at STP? 5. How many moles of hydrogen are in balloon filled to 5.0L STP?

19 Molar volume and density n Molar volume = molar mass/density n Density of gas = molar mass/molar volume n The density of methanol CH 3 OH at 20 o C is g/mL. What is the mass of 0.500L of alcohol at 20 o C? n Do #1-3 page 138

20 Answers to Molar volume L mol 3. a)2.80x10 2 L b) 7.84L C) 95.2L 4. a) mol b) 2.23x10 -4 mol g g g/L x10 24

21 Chemical reactions with gases n Many gases undergo chemical reactions n 2H 2(g) + O 2(g)  2H 2 O (g) n 2 L of hydrogen gas reacts with 1 L of oxygen gas to produe 2 L of water n N 2(g) + 3H 2(g)  2NH 3(g) n Volumes of gaseous substances are consumed and produced.

22 Gay-Lussac’s Law of combining Volumes n Gases combine as volumes and should be in small whole number ratios. n Example: What volume of oxygen gas at STP is required for complete combustion of 4.50L of butane C 4 H 10.

23 Examples n How many litres of water can be made from 24 grams of oxygen gas and 5.0 g of hydrogen gas at STP? Find Limiting?

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

25 Mixed Stoichiometry n Drano contains Al which reacts with excess NaOH to produce bubbles of hydrogen. How many mL of H 2 will be released when 0.150g of Al are dissolved at STP? n 2Al(s)+ 2NaOH(aq) +2H 2 O(l)  3H 2 (g) + 2 NaAlO 2 (aq)

26 Answers to worksheet L 9.7.0L g L mol x L g x g x10 6

27 Examples n Using the following reaction calaculate the mass of sodium hydrogen carbonate necessary to produce 2.87 L of carbon dioxide at 25ºC and 2.00 atm.

28 The Same reaction n What mass of H 2 O will be produced from 65.0 L of O 2 and 75.0 L of NH 3 both measured at STP? n What volume Of NO would be produced? n What mass of NO is produced from 500. L of NH3 at 250.0ºC and 3.00 atm?