Types of Chemical Reactions

Study Notes

Synthesis Reaction: A reaction where two or more substances combine to form a new compound.
- Example: 2H2 + O2 → 2H2O
Decomposition Reaction: A reaction where a single compound breaks down into two or more substances.
- Example: 2H2O → 2H2 + O2
Replacement Reaction: A reaction where one element replaces another element in a compound.
- Example: Zn + CuSO4 → ZnSO4 + Cu
Combustion Reaction: A reaction where a substance reacts with oxygen to produce heat and light.
- Example: 2CH4 + 3O2 → 2CO2 + 3H2O
Neutralization Reaction: A reaction where an acid reacts with a base to produce a salt and water.
- Example: HCl + NaOH → NaCl + H2O
Oxidation-Reduction (Redox) Reaction: A reaction where one substance loses electrons (oxidized) and another substance gains electrons (reduced).
- Example: 2Al + Fe2O3 → 2Fe + Al2O3

Steps to Balance an Equation:
1. Write the unbalanced equation with the reactants on the left and products on the right.
2. Count the number of atoms of each element on both sides of the equation.
3. Identify the elements that are not balanced and add coefficients in front of the formulas of the reactants or products to balance them.
4. Repeat steps 2 and 3 until the equation is balanced.
Tips for Balancing Equations:
- Start with the elements that appear in the greatest number of formulas.
- Balance the elements that are combined in a single formula unit (e.g. water, H2O) last.
- Never change the subscripts of a formula unit.
- Check the equation periodically to ensure that it is balanced.
Example of Balancing an Equation:
- Unbalanced equation: Ca + O2 → CaO
- Balanced equation: 2Ca + O2 → 2CaO

A synthesis reaction combines two or more substances to form a new compound, such as 2H2 + O2 → 2H2O.
A decomposition reaction breaks down a single compound into two or more substances, such as 2H2O → 2H2 + O2.
A replacement reaction involves the replacement of one element with another in a compound, such as Zn + CuSO4 → ZnSO4 + Cu.
A combustion reaction involves the reaction of a substance with oxygen to produce heat and light, such as 2CH4 + 3O2 → 2CO2 + 3H2O.
A neutralization reaction involves the reaction of an acid with a base to produce a salt and water, such as HCl + NaOH → NaCl + H2O.
An oxidation-reduction (redox) reaction involves the loss of electrons by one substance and the gain of electrons by another, such as 2Al + Fe2O3 → 2Fe + Al2O3.

To balance an equation, write the unbalanced equation, count atoms on both sides, identify unbalanced elements, and add coefficients to balance them.
Tips for balancing equations include starting with elements that appear in the greatest number of formulas, balancing elements in a single formula unit last, and never changing subscripts.
The steps to balance an equation are: write the unbalanced equation, count atoms, identify unbalanced elements, add coefficients, and repeat until balanced.
An example of balancing an equation is Ca + O2 → CaO, which becomes 2Ca + O2 → 2CaO.