Chemical Reactions

When a substance undergoes a chemical change.

What is a chemical reaction?

Some clues that a chemical reaction has occurred.

1.Extreme color changes

2.A solid forms

3.Bubbles form.

4.Heat is produced or absorbed.

Chemical equations represent a chemical reaction that takes place.

Example of a Chemical Equation

What are chemical equations?

Reactants are always on the left side of the arrow. They are your starting materials.

Products are always on the right side of the arrow. They are your final product of the chemical reaction.

• In a chemical reaction, atoms are not created or destroyed. They are simply rearranged.

• All atoms present in the reactants must be accounted for in the products. – Same number of each type atom on both sides of arrow

This is called the Law of Conservation of Matter

Physical states of compounds are often given in a chemical equation.

Law of Conservation of Matter – matter is not either created or destroyed during a chemical reaction.

Law of Conservation of Mass – mass is not either created or destroyed during a chemical reaction.

Balancing Chemical Equations

In a chemical reaction, neither mass or matter (atoms) are either created or destroyed. Everything gets rearranged.

This is important to remember.

This is an example of an unbalanced chemical equation. According to the Law of Conservation of Matter, they should be the same number atoms on both sides of the arrow.

This is an example of a balanced chemical equation. This equation follows the Law of Conservation of Matter.

Lets compare the two equations…

CH4 + O2 CO2 + H2O

CH4 + 2O2 CO2 + 2H2O

What is the difference between the two equations?

Lets compare the two equations…

CH4 + O2 CO2 + H2O

CH4 + 2O2 CO2 + 2H2O

A chemical reaction is balanced by using a systematic approach:

Write the formulas of the reactants and products to give the unbalanced chemical equation.

__H2(g) + __ O2(g) __H2O(l)

H:2 H:2O:2 O:1

Using coefficients, balance the chemical equations. At the end check to be sure the equation is balanced. (same numbers of all types of atoms on the reactants and products sides.

2

22

44

Example Problems

1. __BaCO3(s) __BaO(s) + __CO2(s)

2. __Al2O3(s) __Al(s) + __O2(g)

3. __NaI(s) + __Br2(l) __NaBr(s) + __I2(g)

4. __CuBr2(s) + __AlCl3(aq) __CuCl2(aq) + __AlBr3(aq)

5. __C6H14(l) + __O2(g) __CO2(g) + __H2O(l)

6. __C2H2((l) + __O2(g) __CO2(g) + __H2O(l)

There are 5 different types of chemical reactions.

1. Synthesis Reaction2. Decomposition Reaction3. Single Replacement Reaction4. Double Replacement Reaction5. Combustion Reaction

What are the different types of Chemical reactions?

1. Synthesis Reactions (Combining)• A synthesis reaction is a reaction where

simple reactants builds up to make a bigger compound.

• There are more reactants than products.

C(s) + O2(g) CO2(g)

CaO(s) + H2O Ca(OH)2

+

2. Decomposition Reactions (breaking apart)•A decomposition reaction occurs when a compound is broken down into simpler substances.

•There are more products than reactants

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

KClO2(s) KCl(s) + O2(g)

+

3. Single Displacement• One ion is exchanged with another

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

+ +

4. Double Displacement (replacement)

•2 ions are exchanged

HCl (aq) + KOH(aq) HOH(l) + KCl(aq)

+ +

5. Combustion•A reaction in where oxygen (O2) is a reactant

CH4 + 202 CO2 + 2H2O