1. Chemical Reactions

2. What kind of change do the following words suggest?
Burn
Rot
Rust
Decompose
Ferment
Explode
Corrode
Chemical Change – the composition of matter always changes.

3. A chemical reaction occurs when one or more substances (the reactants) change into one or more new substances (the products).
Reactants  Products

4. Word Equation Iron + Oxygen  Iron (III) Oxide
The arrow is read as yields, gives, or reacts to produce.

5. Formula Equations Uses chemical formulas of reactants and products.
Fe + O2  Fe2O3
This is called the skeleton equation because it is not balanced.

6. Law of Conservation of Mass
Atoms are neither created nor destroyed, they are just rearranged. Bonds break and new bonds are formed.
In any chemical change, mass is conserved. The number of atoms in the products are the same as the number of atoms that were in the reactants.

7. Law of Conservation of Mass
If we have 4 atoms of H in the reactants, how many will be in the products?
If we have 2 atoms of H and 2 atoms of Cl in the reactants, how many atoms of each element will we have in the products?

8. Balancing Chemical Equations
A balanced equation has the same number of atoms of each element in both the reactants and products.
Coefficients are whole numbers that are placed in front of formulas in an equation in order to balance it.
Subscripts are never changed to balance equations.

9. Rules for Writing and Balancing Equations
Determine the formulas for all reactants and products
Write the skeleton equation by putting reactants on the left and products on the right with an arrow between.
Determine the # of atoms of each element in the reactants and products.
Balance the elements one at a time by using coefficients.
Make sure the coefficients are in the lowest possible ratio.

10. Fe + O2  Fe2O3 Is this balanced? 1 Fe and 2 O  2 Fe and 3 O
Are the coefficients in the lowest possible ratio? 4 3 2

11. Practice Balancing __ H2 + __O2  __ H2O Reactants: 2 H and 2 O
Products 2 H and 1 O
2 H2 + O2  2 H2O
Reactants: 4 H and 2 O
Products 4 H and 2 O
Remember: You cannot balance the equation by changing the subscripts. Water is not the same as H2O2 (hydrogen peroxide)

12. CuSO4 + Fe  Fe2(SO4)3 + Cu
C2H4 + O2  H2O + CO2

13. Try These 1. __NaCl + __BeF2  __NaF + __BeCl2
2. __FeCl3+__Be3(PO4)2 __BeCl2 + __FePO4
3. __AgNO3 + __LiOH  __AgOH + __LiNO3
4. __CH4 + __O2  __CO2 + __H2O
5. __Mg + __Mn2O3  __MgO + __Mn

14. States of matter symbols used in chemical equations
(s) solid
(l) liquid
(aq) in aqueous solution (dissolved in water)
(g) gas