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Chemical Equations
A balanced chemical equation allows us to calculate:
masses of reactants or products
the % yield of any named product
the % atom economy for industrial processes…read more

Slide 3

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Calculating the Mass of Reactant
10g of sodium chloride is produced when sodium is
burnt in excess chlorine.
What mass of sodium was used?
(Ar values are: Na = 23 Cl = 35.5)
Balanced
equation 2Na(s) + Cl2(g) 2NaCl(s)
Masses 2 x 23 = 46g Na 2(23 + 35.5) = 117g NaCl
117g NaCl is produced by 46g of Na
1g NaCl is produced by 46g Na = 0.39g Na
Calculation 117
Therefore, 10g NaCl is produced by 10 x 0.39g Na
= 3.9g sodium…read more

Slide 4

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Calculating the Mass of Reactant
If 5g of magnesium oxide is produced when
magnesium is burnt in excess oxygen....
What mass of magnesium was used?
(Ar values are: Mg = 24 O = 16)
Balanced 2Mg(s) + O2(g) 2MgO(s)
equation
Masses 2 x 24 = 48g Mg 2(24 + 16) = 80g MgO
80g MgO is produced by 48g Mg
1g MgO is produced by 48g Mg = 0.6g Mg
Calculation 80
Therefore, 5g MgO is produced by 5 x 0.6g Mg
= 3.0g magnesium…read more

Slide 5

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Calculating the Mass of Product
What mass of magnesium oxide is produced when 30g of
magnesium is burnt in oxygen? (Ar values are: Mg = 48 O = 16)
Balanced 2Mg(s) + O2(g) 2MgO(s)
equation
Masses 2 x 24 = 48g Mg 2x (24 + 16) = 80g MgO
48g Mg reacts to produce 80g MgO
1g Mg reacts to produce 80g MgO = 1.66g MgO
48
Calculation
Therefore, 30g Mg reacts to produce 30 x 1.66g MgO
= 49.8g magnesium oxide…read more

Slide 6

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Calculating the Mass of Product
The relative formula mass Mr of a compound is the sum of all the
atomic masses added together.
What mass of sodium chloride is produced when 25g of sodium is
burnt in excess chlorine? (Ar values are: Na = 23 Cl = 35.5)
Balanced
equation 2Na(s) + Cl2(g) 2NaCl(s)
Masses 2 x 23 = 46g Na 2 x (23 + 35.5) = 117g NaCl
46g Na reacts to produce 117g NaCl.
1g Na reacts to produce 117g NaCl = 2.54g NaCl
Calculation 46
25g Na react to produce 25 x 2.54g NaCl
= 63.5g sodium chloride.…read more

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