Chemical Reactions

Chemical Equations• A chemical equation is a representation

of a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).

Fe + O2 Fe2O3

•A Chemical formula is a combination of symbols that

represent the elements in a compound. (add this note to

your reading guide)

All chemical reactions

• have two parts• Reactants - the substances you start

with (the ones reacting)• Products- the substances you end

up with (the ones produced)• The reactants turn into the products.• Reactants ® Products

• A chemical reaction rearranges the atoms of the reactants to form new compounds of the products.

• No new atoms are created, they have only been rearranged.

4 types of Chemical Reactions:

1. Synthesis Reaction: two or more elements or compounds combine to make one more complex substance (A + B → AB)

2. Decomposition Reaction: a compound is broken down into simpler products (AB → A + B)

3. Single Replacement Reactions: replace one element from a compound with another element.

(A + BC B + AC)

4. Double Replacement Reactions: swaps elements between 2 compounds that react together to form two new compounds. (AB + CD AD + CB)

The Law of Conservation of Mass states that:

• The mass of the reactants equals the mass of the products.

OR - • Matter can never be created nor

destroyed OR -• you can’t get somethin’

outta nothin’(hahaha)

Word Equations

• ExampleMethane + Oxygen Carbon dioxide +

Water

• The arrow means yields, gives, or reacts to produce.

Rules for balancing

1 Write the correct formulas for all the reactants and products

2 Count the number of atoms of each type appearing on both sides

3 Balance the elements one at a time by adding coefficients (the numbers in front)

4 Check to make sure it is balanced.

Never

• Change a subscript to balance an equation.

• If you change the formula you are describing a different reaction.

• H2O is a different compound than H2O2

• Never put a coefficient in the middle of a formula

• 2 NaCl is okay, Na2Cl is not.

• What is a coefficient? A number that indicates how many atoms of an element are in one molecule

• What is a subscript? Numbers telling how many molecules are involved in a chemical reaction