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 + O 2  Fe 2 O 3 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) 1.Decomposition Reaction: a compound is broken down into simpler products (AB → A + B) 2.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 Example Methane + Oxygen  Carbon dioxide + Water The arrow means yields, gives, or reacts to produce.

Rules for balancing  Write the correct formulas for all the reactants and products  Count the number of atoms of each type appearing on both sides  Balance the elements one at a time by adding coefficients (the numbers in front)  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. H 2 O is a different compound than H 2 O 2 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