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

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A process in which at least one new substance is produced as a result of chemical change– Reactants used.– Products formed.

In a Chemical Reaction:

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Reactants Products

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Ingredients:12 oz of dough4 oz mushroom12 slices pepperoni8 oz cheese5 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?

Analogy

12 oz dough + 4 oz mushroom + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce 1 pizza

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).

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Constructing Chemical Equations

2Mg (s) + O2(g) 2MgO (s)

Reactants Products

State symbolsState symbols

Eg:

Constructing Chemical Equations

The Reaction Between Hydrogen and Oxygen• Word equation:

• Chemical equation:hydrogen + oxygen water

2H2(g) + O2(g) 2H2O(l)

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State symbolState symbol

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.0has the same number of atoms of each element on

both sides of the equation.

Law of Conservation

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Balancing equation

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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.

Balancing equation

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Step

1 Write down the formula of the reactant and products.

Methane + oxygen carbon dioxide + water

CH4 + O2 CO2 + H2O

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Balancing equation

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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

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C atom = 1H atoms = 4O atoms = 2

C atom = 1H atoms = 2O atoms = 2 + 1 = 3

Balancing equation

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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 + O2 CO2 + H2O

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C atom = 1H atoms = 4O atoms = 4

C atom = 1H atoms = 4O atoms = 4

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Balancing equation

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Step4 Includes the state symbols in the equation.

CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (g)

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Learning Check for Balancing Equation

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Step

1 Write down the formula of the reactant and products.

aluminium + chlorine gas aluminium chloride

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Al + Cl2 AlCl3

Balancing equation

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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

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Al atom = 1Cl atoms = 2

Al atom = 1Cl atoms = 3

Balancing equation

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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.

Al + Cl2 AlCl323

Al atom = 2Cl atoms = 6

Al atom = 2Cl atoms = 6

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Balancing equation

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Step4 Includes the state symbols in the equation.

2Al (s) + 3Cl2 (g) 2AlCl3 (s)

Learning check for Balancing equation

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Write the balanced chemical equation with state symbol.

Iron + oxygen gas Iron(III) oxide4Fe (s) + 3O2 (g) 2Fe2O3 (s)

Sodium + bromine sodium bromide2Na (s) + Br2 (l) 2NaBr (s)

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.

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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.