1. No category

Molar Quantities:
Balancing Equations
CH4 + O2 = CO2 + H2O
Count the atoms on
each side of the equation.
Reactants: 1 C ; 4 H ; 2 O
Products: 1 C ; 2 H ; (2 + 1) = 3 O
Reactants: 1 C ; 4 H ; 2 O
Products: 1 C ; 2 H ; (2 + 1) = 3 O
Double the H in the products:
CH4 + O2 = CO2 + 2 H2O
Reactants: 1 C ; 4 H ; 2 O
Products: 1 C ; 4 H ; (2 + 2) = 4 O
Reactants: 1 C ; 4 H ; 2 O
Products: 1 C ; 4 H ; (2 + 2) = 4 O
Double the O in the reactants:
CH4 + 2 O2 = CO2 + 2 H2O
Reactants: 1 C ; 4 H ; 4 O
Products: 1 C ; 4 H ; 4 O
CH4 + 2 O2 = CO2 + 2 H2O
Molar coefficients
for this reaction are:
1 CH4 : 2 O2 : 1 CO2 : 2 H2O
Molar coefficients are used for calculations.
1 CH4
+ 2 O2 = 1 CO2 + 2 H2O
 1 mole of methane gas (CH4) combines with
 2 moles of oxygen gas (O2) to produce
 1 mole of carbon dioxide (CO2) gas and
 2 moles of water vapor (H2O).
 What if we had only 0.5 moles of CH4 ???
 How much CO2 would be produced ??
CH4 + 2 O2 = CO2 + 2 H2O
 (0. 5 moles CH4) x [ 1 mole CO2 / 1 mole CH4 ]
= 0.5 moles CO2
* Note: Moles CH4 cancel out.
 What if we had only 0.5 moles of CH4 ???
 How much H20 would be produced ??
CH4 + 2 O2 = CO2 + 2 H2O
(0. 5 moles CH4) x [ 2 mole H2O / 1 mole CH4 ]
= 1.0 moles H2O
*Note: Moles CH4 cancel out.
•
Because atoms are so small, the normal units
of mass -- the gram and the kilogram -are much too large to be convenient.
•
One mole of something consists of
6.02 x 1023 units of that substance.
One mole of carbon contains
6.02 x 1023 atoms of carbon.
One mole of water contains
6.02 x 1023 molecules of water.
•
•
Molar Mass (or molecular weight ) of a
molecule or compound is obtained by
summing the molar masses
of the atoms of the compound.
Molar masses of the elements
are located below the element’s symbol
in the Periodic Table of the Elements.
1 mole of CH4 molecules contains :
1 mole of carbon C atoms and
4 moles of hydrogen H atoms.
Mass of 1 mol of methane:
Sum of the masses
C atoms and H atoms.
1 mol C = 1 x 12.01 g = 12.01 g
4 mol H = 4 x 1.008 g = 4.032 g
1 mol CH4 = 16.04 g
 What if I do not know how many moles of
reactant I have ? What if, instead, I have:
200 g of CH4 = ???? moles CH4
 In a mole-mass calculation, we have the
added burden of converting mass to moles.
 For this, we need the molar masses of
the reactants and/or products.
What if I have: 200 g of CH4 ?
How many moles of CH4 is that ?
Molar mass of CH4 = 16.0 g / mol
( 200 g ) x ( 1 mol / 16.0 g )
= 12.5 mol CH4
*Note: Inversion of the molar mass
How many moles of CO2
will be produced
by 12.5 moles of CH4 ??
CH4 + 2 O2 = CO2 + 2 H2O
(12.5 moles CH4) x [ 1 mole CO2 / 1 mole CH4 ]
= 12.5 moles CO2
How many grams in 12.5 moles of CO2 ?
Molar mass of CO2:
Mass of 1 mol C = 1 x 12.0 g = 12.0 g
Mass of 2 mol O = 2 x 16.0 g = 32.0 g
Mass of 1 mol CO2 = 44.0 g
( 12.5 mol ) x ( 44.0 g / mol )
= 550 g CO2
Don’t forget about the most important part
of any fuel combustion reaction such as :
CH4 + 2 O2 = CO2 + 2 H2O
It produces heat !!
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