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By the end of the period, I will be able to…

Based on observations, determine whether a chemical reaction has occurred

Use appropriate terminology to describe chemical reactions

Write word, skeleton, and balanced chemical equations using the IUPAC nomenclature system

Learning Goals

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Writing Chemical Equations

~ Word Equations

~ Skeleton Equations

~ Balanced Equations

How do you know whether the change you are observing is a chemical or physical change?

Figure 1:

The wax of this candle is undergoing both physical and chemical changes.

Which change results in new substances?

Which does not?

Signs of Chemical Reactions

Change in Colour

Change in Odour

Production of new gases,

vapours or solid

(precipitate)

Release or

absorption of

energy (light, heat,

electricity, or

sound)

Difficult to Reverse

Representing Chemical Change

Word Equation

Skeleton Equation

Balanced Equation**Important that you can work back and forth between these types of chemical equations**

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Chemical Reaction – is a process in which substances interact, causing different substances with different properties to form

Reactant – a starting substance in a chemical reaction

Product – a substance that is formed in a chemical reaction

Chemical Equation – a condensed statement that expresses chemical change using symbols and chemical names or formulas

Describing Chemical Reactions

Writing Word Equations

A WORD EQUATION describes chemical change using the names of the reactants and products

Example 1

Write the word equation for the reaction of methane gas a oxygen to form carbon dioxide and water.

Methane + oxygen carbon dioxide + water

REACTANTS PRODUCTS

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Symbol Purpose

+ Indicates that two or more reactants or products are involved

→ Shows the direction of the chemical change that is taking place. The arrow stands for yields or reacts to produce.

⇋ Indicates a reversible reaction

(s) Identifies a solid state(l) Identifies a liquid state(g) Identifies a gas state(aq) Identifies an aqueous solution

Symbols Used in Chemical Equations

Writing Skeleton Equations A SKELETON EQUATION is chemical equation in

which the reactants and products in a chemical reaction are represented by the chemical formulas; their relative quantities are not included

Word EquationMethane + oxygen carbon dioxide + water

Chemical EquationCH4(g) + O2(g) CO2(g) + H2O(g)

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Problem

When solid sodium carbonate is added to an aqueous solution of hydrochloric acid, liquid water, carbon dioxide gas, and an aqueous solution of sodium chloride are formed.

What is the skeleton equation or this chemical reaction?

PRACTICE – Writing Skeleton Equations

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Determine the chemical formula for each

substance. Include the state.

Solid sodium carbonate: Na2CO3(s)

Aqueous solution of hydrochloric acid: HCl(aq)

Liquid water: H2O(l)

Carbon dioxide gas: CO2(g)

Aqueous solution of sodium chloride: NaCl(aq)

PRACTICE – Writing Skeleton Equations

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Na2CO3(s) + HCl(aq) H2O(l) + CO2(g) + NaCl(aq)

PRACTICE – Writing Skeleton Equations

Check Your Solution

The reactants are written on the left side of the arrow, and the products are written on the right side. The chemical formula for each substance is written correctly. The physical state of each reactant and product is shown.

Writing Balanced Chemical Equations A BALANCED CHEMICAL

EQUATION is a statement that uses chemical formulas and coefficients to show the identities and ratios of the reactants and products in a chemical reaction

Chemical EquationCH4(g) + O2(g) CO2(g) + H2O(g)

Equation is NOT balanced

Why?

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COEFFICIENT in a balanced chemical equation, a positive number that is placed in front of a formula to show the relative number of particles of the substance that are involved in the reaction.

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

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Did I write out the word equation?Is the skeleton equation written correctly?

Chemical formulas correct – criss-cross rule?Are the states included?Are the reactants and products on the correct side of

the yield arrow?

Is the skeleton equation already balanced?If not balanced, add coefficients to balanceDouble checkState type of reaction

Balanced Equations Success Criteria