Chemical Reactions

In chemical reactions, one or more substances

change into different substances.

example: combustion

Word Equations and Chemical Equations

Chemists use equations to describe chemical reactions.

Word equations show the names of the materials in the chemical reaction.

Chemical equations show the chemical formulas of the materials in the chemical reaction.

(starting materials) (yields) (ending materials)

REACTANT PRODUCTS

Common State Symbols in Chemical Equations

State Symbol Meaning Example

Solid

Liquid

Gaseous

Aqueous (dissolved in water)

(s)(l)

(g)

(aq)

(sodium chloride) NaCl(s)

(bromine) Br2(l)

(hydrogen) H2 (g)

(aqueous sodium chloride solution) NaCl(aq)

Word equation:

sodium

chlorine chemical reaction

sodium chloride

sodium(s) + chlorine(g) sodium chloride(s)

Chemical equation:

Na(s) + Cl2(g) NaCl(s)

Examples:

zinc + copper(II) sulphate

Word equation:

Chemical equation:

Zn(s) + CuSO4(aq)

zinc sulphate + copper + energy

ZnSO4(aq) + Cu(s) + energy

zinc

copper(II) sulphate

zinc sulphate

copper

Consider the following reaction: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

1. Name the reactants and products in this reaction.

2. Name the chemicals that are dissolved in water.

3. Name the white solid.

4 What physical properties do both reactants have in common?

Practice

Write the word equations:

The Law of Conservation of Mass

Chemist Antoine Lavoisier’s work in the 1700s resulted in the Law of Conservation of Mass. It states that:

In a chemical reaction, the total mass of the products is always the same as the total mass of the reactants.

For example: The electrolysis of water

H2O H2 + O2 is NOT a balanced chemical equation.

Why? Because the number of H and O atoms in the reactants does not equal the number of H and O atoms in the products.

How can we make a balanced chemical equation?

Balancing Chemical EquationsThe electrolysis of water yields oxygen gas and hydrogen gas.

a) Write the word equation.

water oxygen + hydrogen

b) Write the skeleton equation.

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

c) Write the balanced chemical equation.

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

Iron reacts with oxygen to produce Iron (III) oxide (Fe2O3)

a) Write the word equation.

iron + oxygen iron (III) oxide

b) Write the skeleton equation.

Fe + O2 Fe2O3

c) Write the balanced chemical equation.

4Fe + 3O2 2Fe2O3

PracticeFor the following reactions, write:

the word equation the skeleton equation (unbalanced chemical equation) the balanced equation

1. Potassium hydroxide and hydrogen are produced when potassium is placed in water.  2K + 2H2O 2KOH + H2

2. The iron reacts with oxygen to produce rust, which is iron (III) oxide.

4Fe + 3O2 2Fe2O3

3. Zinc reacts with lead (IV) nitrate to produce zinc nitrate and lead.

  

2Zn + Pb(NO3)4 2Zn(NO3)2 + Pb

4. Calcium chloride reacts with silver nitrate to produce a white precipitate, silver chloride, and calcium nitrate.

  

CaCl2 + 2AgNO3 2AgCl + Ca(NO3)2

5. Calcium carbonate decomposes into calcium oxide and carbon dioxide.

CaCO3 CaO + CO2

6. Carbon monoxide and hydrogen gases are produced when carbon is placed in water.

C + H2O CO + H2

7. In a hydrogen bomb, hydrogen gas and oxygen reacted to make water.

2H2 + O2 2H2O

 

8. Nitrogen monoxide from automobile exhaust reacts with oxygen to produce nitrogen dioxide, which is a toxic brown gas.

2NO + O2 2NO2

9. Hydrogen sulphide can be broken into hydrogen gas and sulphur.

H2S H2 + S

  

10. Calcium metal and water combine to produce calcium hydroxide and hydrogen gas.

Ca + 2H2O Ca(OH)2 + H2