Indicators of a chemical reaction-• Color change• Producing a gas• Heat/light energy released• Formation of a precipitate

Chemical equation - Describes a chemical change.

Parts of an equation:

Zn + 2HCl ZnCl2 + H2

Reactant Product

Reaction symbol

Coefficient

Reactant - The chemical(s) you start with before the reaction.Written on left side of equation.

Product - The new chemical(s) formed by the reaction.Right side of equation.

Subscript - shows how many atoms of an element are in a molecule.EX: H2O

2 atoms of hydrogen (H)1 atom of oxygen (O)

Coefficient - shows how many molecules there are of a particular chemical.EX: 3 H2O

6 atoms of hydrogen (H)3 atoms of oxygen (O)

2H2 + O2 2H2O

Lavoisier: Matter is neither created nor destroyed in a chemical reaction.In other words, the number and type of atoms

going INTO a reaction must be the same as the number and type of atoms coming OUT.

If an equation obeys the Law of Conservation, it is balanced.

CH4 + O2 CO2 + H2O

Reactant Side Product Side

1 carbon atom4 hydrogen atoms2 oxygen atoms

1 carbon atom2 hydrogen atoms3 oxygen atoms

A Balanced Equation

CH4 + 2O

2 CO

2 + 2H

2O

Reactant Side Product Side

1 carbon atom4 hydrogen atoms4 oxygen atoms

1 carbon atom4 hydrogen atoms4 oxygen atoms

1. Matter cannot be created or destroyed.2. Subscripts cannot be added, removed, or changed.3. You can only change coefficients.4. Coefficients can only go in front of chem. formulas...NEVER in the middle of a formula.A few extra tips:

Try balancing big formulas first; save free elements for last.If the same polyatomic ion appears on both sides of the equation, it’s usually okay to treat it as one unit.There is no one particular way to balance equations. Some equations are harder to balance than others and might require some creativity to solve.

Balance the following equation by adjusting coefficients.

reactants products

N

H

NN22 + H + H22 NH NH

33

2

2

1

3

22

2

6

33

6

Balance the following equation by adjusting coefficients.

KClOKClO33 KCl + O KCl + O

22reactants products

K

Cl

O

1

1

1

1

3 2

3322

2

2

6 6

2

2

22

Balance the following equation: C2H6 + O2 CO2 + H2O44 667722

Balance the following equation: Fe + O2 Fe2O3223344

Chemical Reaction Types• synthesis – reaction where 2 or more substances combine to

form one• A + B → AB• Ex: 2H

2 + O

2 → 2H

2O

• decomposition – reaction where a compound decomposes(breaks apart) into multiple substances

• AB → A + B• Ex: 2KClO3 → 2KCl + 3O2

• single replacement - single element replaces another element in a compound

• A + BC → AC + B• Ex: 2Ag + FeCl

2 → Fe + 2AgCl

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Chemical Reaction Types Continued…• Double replacement - two elements in different

compounds switch places• AB + CD → AD + BC• Ex: NaOH + HCl → NaCl + HOH(H

2O)

• Combustion Reaction - Hydrocarbon combines with oxygen to form water and carbon dioxide• hydrocarbon – any compound made from carbon and

hydrogen• hydrocarbon + O2 → CO2 + H2O

• Ex: C2H4 + 3O2 → 2CO2 + 2H2O

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