Chemical formulae and 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… Construct chemical equations, with state symbols, including ionic equations. Interpret chemical equations with state symbols. Construct ionic chemical equations.

sodium + chlorine  sodium chloride 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

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 Qs that can be asked: A. How does an equation indicate a change in the identity of the reacting substances? The formulas of the reactants are different than the formulas of the products. B. How did the pink and blue reactants combine? 1 pink combined with 1 blue C. Did all the reactants form product? Why or why not? No. There were more pink than blue.

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

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) 2MgO (s) State symbols

Constructing Chemical Equations The Reaction Between Hydrogen and Oxygen Word equation: Chemical equation: hydrogen + oxygen water State symbol 2H2(g) + O2(g) 2H2O(l) Ask student to state the formula of the compound for the chemical equation.

Constructing Chemical Equations Balancing Equations All chemical equations (with state symbols) must be balanced. A balanced equation: shows the formulae of all the reactants and all the products in a reaction. has the same number of atoms of each element on both sides of the equation.

Law of Conservation

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.

Methane + oxygen  carbon dioxide + water Balancing equation Step 1 Write down the formula of the reactant and products. Methane + oxygen  carbon dioxide + water CH4 + O2  CO2 + H2O 13

Not Balanced 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 Not Balanced 14

Balanced 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 + O2  CO2 + H2O 2 2 C atom = 1 H atoms = 4 O atoms = 4 C atom = 1 H atoms = 4 O atoms = 4 Balanced 15

CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g) Balancing equation Step 4 Includes the state symbols in the equation. CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g) 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

Not Balanced 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 Not Balanced 18

Balanced 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. Al + Cl2  AlCl3 2 3 2 Al atom = 2 Cl atoms = 6 Al atom = 2 Cl atoms = 6 Balanced

Balancing equation Step 4 Includes the state symbols in the equation. 2Al (s) + 3Cl2 (g)  2AlCl3 (s)

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) Ask someone to do on the big whiteboard

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.

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.