CHEMICAL REACTIONS

Chemical Equations Chemical Equations are used to represent

chemical reactions.Reactants Products

Law of Conservation of Matter means matter cannot be created or destroyed during a chemical reaction.

We must balance chemical reactions (add coefficients) to comply with the law.

Chemical Equations (Cont) Example:

CH4 + O2 CO2 + H2OMethane + Oxygen Carbon + Water

DioxideReactants Products1 – C 1 – C4 – H 2 – H2 – O 3 – O

Balancing

Chemical reactions change the groupings of the atoms, but DO NOT create or destroy atoms, so there must be the same number of each type of atom on each side of the arrow. We must use coefficients to Balance a Chemical Equation

Balancing Chemical Equations

1. Determine the correct formula for each reactant and product by supplying the subscripts to the formulas.

Once you write the correct formula, DO NOT change the subscripts.

2. Add coefficients in front of balanced formulas to give the same number and kind of atoms on both sides.

Use the lowest possible ratio of coefficients.

Example

CH4 + 2 O2 CO2 + 2 H2O

If I place a 2 in front of the O2 and the H2O, then I end up with:

Reactants Products1 – C 1 – C4 – H 4 – H4 – O 4 – O

You Try this One

C2H4 + O2 CO2 + H2O2 – C - 14 – H - 22 – O - 3

C2H4 + 3O2 2CO2 + 2H2O2 – C - 24 – H - 46 – O - 6

Another Example

C3H6 + O2 CO2 + H2O3 – C - 16 – H - 24 – O - 3

2 C3H6 + 9 O2 6 CO2 + 6 H2O6 – C - 6

12 – H - 1218 – O – 18

You Try This One

What would the coefficients be for this reaction:

PCl5 + H2O H3PO4 + HCl 1, 4, 1, 5

Physical States Symbols in parentheses after each

formula:1. Solid (s)2. Liquid (l)3. Gas (g)4. Aqueous (aq)

1. Aqueous means dissolved in water.

– Example:2 H2O2 (aq) 2 H2O (l) + O2 (g)

Word Equations Chemical Equations written out as

words. This is a statement that describes the chemical equation in place of using symbols.

Steps:1. Using the words, write the correct

formulas in the correct locations.2. Add the states of matter abreviations.3. Balance the equation.

Words to watch for States of matter – This is a symbol that is

used to identify the state of matter for each substance in a reaction.

Gas, Liquid, Solid, Aqueous Gas (g) Liquid (l) Solid (s) may also be called a Precipitant (ppt) or

a crystal (c) Aqueous (aq) means dissolved in water.

Example 1 Solid Zinc reacts with Hydrochloric Acid to produce

Zinc Chloride and Hydrogen gas. Zinc + Hydrochloric Acid Zinc Chloride + Hydrogen

Zn (s) + HCl (aq) ZnCl2 (aq) + H2 (g)

Zn(s) + 2 HCl (aq) ZnCl2 (aq) + H2(g)

You Try This One Solid Calcium Oxide reacts with solid

Aluminum to produce solid Aluminium Oxide and Calcium.

calcium oxide + aluminum → aluminum oxide + calcium

CaO (s) + Al (s) Al2O3 (s) + Ca (s)

3CaO (s) + Al (s) Al2O3 (s) + 3Ca (s)

Example 2 Aqueous Lead (II) Nitrate reacts with

aqueous Sodium Sulfate to produce aqueous Sodium Nitrate and solid Lead (II) Sulfate.

Lead (II) Nitrate + Sodium Sulfate Sodium Nitrate + Lead (II) Sulfate

Pb(NO3)2 (aq) + Na2SO4 (aq)

→ NaNO3 (aq) + PbSO4 (s)

Pb(NO3)2 (aq) + Na2SO4 (aq)

→ 2 NaNO3 (aq) + PbSO4 (s)

You Try This One Sodium Phosphate and Copper (II) Sulfate react

in water to produce aqueous Sodium Sulfate and solid Copper (II) Phosphate.

sodium phosphate + copper (II) sulfate → sodium sulfate + copper (II) phosphate

Na3PO4 + CuSO4 → Na2SO4 + Cu3(PO4)2