chemical equations

Chemical Equations

At the end of this lesson, you should be able to..

construct balanced chemical equations with state symbols.

An equation represents what occurs in a chemical reaction.

Can be written using words or chemical formulae

Word Equation:

Sodium + Hydrochloric acid Sodium chloride + Hydrogen

Chemical Equation:

2 Na + 2 HCl 2 NaCl + H2

2Na + 2HCl 2NaCl + H2

(s) (aq)

(aq)

(g)

Reacting substances,

or reactants are on the left-hand side of

the equation.

Products or substances formed are on the right-hand side

of the equation.

The arrow means ‘react to form’ The reaction proceeds from left to right.

Sodium and hydrochloric acid react to form sodium chloride and hydrogen.

Step 1: Write down the chemical formulae of the reactants and products.

Step 2: Balance the equation.

Step 3: Write down the state symbols.

In a chemical reaction, substances are changed into other substances. No matter is created nor destroyed.

i.e. the number of atoms before and after the reaction remains the same.

Marks can be penalized if you give the wrong state symbols, even when the

question did not ask for it!

Liquid state (l): Pure substance that is in liquid form

Aqueous state (aq): Substance dissolved in water

Is the substance soluble in water?

Many ionic compounds are soluble in water.

Most covalent compounds are not soluble in water.

SOLUBLE covalent compounds

Magnesium reacts with sulphuric acid to form magnesium sulphate and hydrogen.

Sulfuric acid reacts with sodium hydroxide to form sodium sulfate and water.

Soluble InsolubleAll Sodium All PotassiumAll Ammonium

All nitrates

Sulphates except

Chlorides exceptIodides exceptBromides except

Carbonates except SPAHydroxides except SPAOxides except SPA

PbSO4 and BaSO4

PbCl2 and AgClPbI2 and AgIPbBr2 and AgBr