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6.2 Gases Avogadro’s Theory
and Molar Volume
Law of Combining Volumes (Joseph Gay –Lussac )
• When measured at the same temperature and pressure, volumes of gases react in simple whole number ratios.
• 2H2O(l) 2H2(g) + O2(g) (This reaction always produced twice as much hydrogen as oxygen)
http://www.carlton.paschools.pa.sk.ca/chemical/molemass/avogadro.htm
Avogadro’s Theory
• Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
p://www.carlton.paschools.pa.sk.ca/chemical/molemass/avogadro.htm
Fill in the table below___C8H18(l) +___O2(g) ___CO2(g)+ ___H2O(g)
2 mol 25 mol mol ____mol
2 mol mol mol ____mol
___ L 25 L _____ L 18 L
8 L ____L 64 L ____L
____L 5L ____ L ____L
250 mL _____mL ____mL ____mL
Fill in the table below___C8H18(l) +____O2(g) ___CO2(g)+ ___H2O(g)
2 mol 25 mol mol ____mol
2 mol mol mol ____mol
___ L 25 L _____ L 18 L
8 L ____L 64 L ____L
____L 5L ____ L ____L
250 mL _____mL ___ mL ____mL
Fill in the table below___C8H18(l) +__ O2(g) ___CO2(g)+ ___H2O(g)
2 mol 25 mol mol ____mol
2 mol mol mol ____mol
___ L 25 L _____ L 18 L
8 L ____L 64 L ____L
____L 5L ____ L ____L
250 mL _____mL _____mL ____mL
Fill in the table below___ C8H18(l) + ___O2(g) ___CO2(g)+ __H2O(g)
2 mol 25 mol mol ____mol
2 mol mol mol ____mol
___ L 25 L _____ L 18 L
8 L ____L 64 L ____L
____L 5L ____ L ____L
250 mL _____mL ____mL ____mL
Fill in the table below2 C8H18(l) + 25 O2(g) 18 H2O(g) + 16 CO2(g) 2 mol 25 mol 18 mol 16 mol
4 mol 50 mol 36 mol 32mol
2 vol 25 vol 18 vol 16 vol
2 L 25 L 18 L 16 L
4L 50L 36 L 32 L
0.5L 6.25 L 4.5 L 4 L
Another site with VSEPR
• http://www.alevelchemistry.co.uk/module_1.htm
• General site with 3D shapes, and a variety of info.
• http://www.tannerm.com/
Molar Volume
• -The volume of one mole of any gas at a specific temperature and pressure
• @STP 22.4 L/mol
• @SATP 24.8 l/mol
• Remember STP is zero celsius and 101.3kPa
• And SATP(ambient) is 25 celsius and 100kPa
Calculations with molar volume
• n= v volume and n=m
• V molar volume M
• So v = m
• V M
Try this:
• Example 1:• What volume is occupied by 0.024 mol of
nitrogen gas at STP?(ANS: 0.54 L)
• Example 2:• How many moles of nitrogen dioxide are there in
75 L of the gas at SATP?(ANS: 3.02 mol)
Try this:
• Example 1:• What volume is occupied by 0.024 mol of
nitrogen gas at STP?(ANS: 0.54 L)
• Example 2:• How many moles of nitrogen dioxide are there in
75 L of the gas at SATP?(ANS: 3.02 mol)
Try this:
• Example 1:• What volume is occupied by 0.024 mol of
nitrogen gas at STP?(ANS: 0.54 L)
• Example 2:• How many moles of nitrogen dioxide are there in
75 L of the gas at SATP?(ANS: 3.02 mol)
• #1 Answer
• n= v 0.024 mol = __v___
• V 22.4 L/mol
• 0.54 L = v
• #2 Answer
• n= v n= 75 L
• V 24.8 L/mol
• n= 3.02 mol
• volume
• mass mol particles
• concentration
• Example #3
• What volume of balloons does 7.00 g of helium gas fill at SATP?
v=?
m= 7.00 g
M= 4.00 g/mol
V= 24.8 L/mol(Ans 43.4 L)
Practise Questions:
• P 210-211 19 0.73 L
20 5.39 x 10 5 L
21 5.09 x 10 5 L
22 2.5 x 10 5 g
15a 124 kL
15b 250L
15c 325L , 163L
Remember to use ratios