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