Download Chemical formulae and chemical equations

Chemical formulae and chemical
equations
Chemical equations
Review of Prior knowledge
Can you write the chemical formula of the
following substances?
• Magnesium chloride
• Carbon dioxide
• Methane
• Aluminium Sulfate
Welcome to the 101th CVSS
chemistry awards.
• To find out if you have been nominated for
most outstanding chemistry award please
check under your desk.
Objectives for the day…
1. Construct chemical equations, with state
symbols, including ionic equations.
2. Interpret chemical equations with state
symbols.
3. Construct ionic chemical equations.
Objective 1: Constructing chemical equations, with
state symbols, including ionic equations
• An equation can be written in words – a word
equation.
sodium + chlorine  sodium chloride
• An equation can also be written with symbols
and formulae instead of words – a chemical
equation.
2Na + Cl2  2NaCl
5
In a Chemical Reaction:
A process in which at least one new substance is
produced as a result of chemical change
– Reactants used.
– Products formed.
Reactants
Products
6
Analogy
Ingredients:
12 oz of dough
4 oz mushroom
12 slices pepperoni
8 oz cheese
5 oz tomato sauce
These ingredients are used to make a pizza.
How would you write the recipe in word equation
for putting together a pizza?
12 oz dough + 4 oz mushroom + 12 slices pepperoni + 8 oz
cheese + 5 oz tomato sauce  1 pizza
7
Constructing Chemical Equations
What Chemical Equations Show
• The reactants used.
• The products formed.
• The states of the reactants and products.
• The arrow means ‘react to form’ and reaction
proceeds from left to right).
Reactants
Products
Eg: 2Mg (s) + O2(g)
State symbols
2MgO (s)
8
Constructing Chemical Equations
The Reaction Between Hydrogen and Oxygen
• Word equation:
hydrogen + oxygen
water
State symbol
• Chemical equation:
2H2(g) + O2(g)
2H2O(l)
9
Constructing Chemical Equations
Balancing Equations
• All chemical equations (with state symbols) must
be balanced.
• A balanced equation:
0 shows the formulae of all the reactants and all the
products in a reaction.
0 has the same number of atoms of each element on
both sides of the equation.
Law of Conservation
11
Balancing equation
Step
1
Write down the formula of the reactant and products.
2
Check the number of atoms of each element on both
sides of the equation. If the equation is not balanced,
proceed to step 3.
3
Balance the equation by placing numbers in front of
the formulae of the substances in the equation. The
number ‘1’ is not written.
4
Includes the state symbols in the equation.
12
Balancing equation
Step
1
Write down the formula of the reactant and
products.
Methane + oxygen  carbon dioxide + water
CH4 + O2  CO2 + H2O
13
13
Balancing equation
Step
2
Check the number of atoms of each element on
both sides of the equation.
If the equation is not balanced, proceed to step 3.
CH4 + O2  CO2 + H2O
C atom = 1
H atoms = 4
O atoms = 2
C atom = 1
H atoms = 2
O atoms = 2 + 1 = 3
14
14
Balancing equation
Step
3
Balance the equation by placing numbers in front of
the formulae of the substances in the equation. The
number ‘1’ is not written.
CH4 + 2 O2  CO2 + 2H2O
C atom = 1
H atoms = 4
O atoms = 4
C atom = 1
H atoms = 4
O atoms = 4
15
15
Balancing equation
Step
4
Includes the state symbols in the equation.
CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g)
16
16
Learning Check for
Balancing Equation
Step
1
Write down the formula of the reactant and
products.
aluminium + chlorine gas  aluminium chloride
Al + Cl2  AlCl3
17
17
Balancing equation
Step
2
Check the number of atoms of each element on
both sides of the equation.
If the equation is not balanced, proceed to step 3.
Al + Cl2  AlCl3
Al atom = 1
Cl atoms = 2
Al atom = 1
Cl atoms = 3
18
18
Balancing equation
Step
3
Balance the equation by placing numbers in front of
the formulae of the substances in the equation. The
number ‘1’ is not written.
2 Al + 3 Cl2  2 AlCl3
Al atom = 2
Cl atoms = 6
Al atom = 2
Cl atoms = 6
19
Balancing equation
Step
4
Includes the state symbols in the equation.
2Al (s) + 3Cl2 (g) 
2AlCl3 (s)
20
Learning check for Balancing
equation
Write the balanced chemical equation with state
symbol.
Iron + oxygen gas  Iron(III) oxide
4Fe (s) + 3O2 (g)  2Fe2O3 (s)
Sodium + bromine  sodium bromide
2Na (s) + Br2 (l)  2NaBr (s)
21
Learning Objective 2: Interpret chemical
equations with state symbols
2Na + Cl2  2NaCl
• Two atoms of Na react with one molecule of Cl2to
produce 2 unit of NaCl.
22
What did we learn this lesson…
•
•
•
•
•
What is a word equation.
What is a chemical equation.
What is a reaction (reactants and products).
What is law of conservation.
How to write a balanced equation with state
symbols.
• How to deduce a chemical equation.