1. Chemical Equations

2. Chemical Reaction Reaction where something changes into something new
Composition and chemical properties change

3. Practice Problems
Which of the following are examples of chemical reactions?
Wood burning
Baking cookies
Freezing water
Evaporating alcohol
Iron rusting
Dissolving salt in water

4. A2 + 2BC  2BA + C2
Reactants- substances that exist before a chemical change
Left side of arrow in chemical equation
Products- substances that are formed during the chemical changes
Right side of arrow in chemical equation
Arrow = yields (makes)

5. Law of Conservation of Mass/Matter
Matter cannot be created or destroyed, but can be rearranged to create new substances
Therefore, the atoms of matter must be the same on both sides of the chemical equation
Rearranged to produce new compounds
A2 + 2BC  2BA + C2

6. Balancing Equation A2 + BC  BA + C2 A2 + 2BC  2BA + C2
Follows Law of Conservation of Matter
the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product
A2 + BC  BA + C2
A2 + 2BC  2BA + C2

7. Steps to Balance Equations:
Write the correct formula for all reactants and products.
In nature, some elements exist as diatomic elements (two atoms of the same element bonded together)
Oxygen, nitrogen, hydrogen, fluorine, chlorine, bromine, and iodine
Example: Balance the equation for the reaction between chlorine and sodium bromide that produces sodium chloride and bromine.
Cl2 + NaBr  NaCl + Br2

8. ___Cl2 + ___NaBr  ___NaCl + ___Br2 ___Cl2 + 2 NaBr  2 NaCl + ___Br2
2. Determine coefficients that make the equations balance.
coefficients are written in front of the formulas to balance the atoms (the formula itself is never altered)
___Cl2 + ___NaBr  ___NaCl + ___Br2
___Cl NaBr  2 NaCl + ___Br2

9. 3. Showing energy/heat changes in chemical reaction
Endothermic- energy is absorbed or used by reactants
Write heat/energy on reactant side
Exothermic- energy is released
Write heat/energy on product side
Example: CH4 + O2  CO2 + H20
CH4 + O2  CO2 + H20 + heat

10. Cl2 (g) + NaBr (s)  NaCl (s)+ Br2 (l)
4. Showing phases of matter in chemical reactions
Written behind chemical formula
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq) – compound is dissolved in water
Example: Cl2 + NaBr  NaCl + Br2
Cl2 (g) + NaBr (s)  NaCl (s)+ Br2 (l)

11. Balancing Equations Practice
____ P + ____O2  ____P2O5

12. Balancing Equations Practice
____CH4 + ____O2  ____CO2 + ____H2O

13. Balancing Equations Practice
____FeO3 + ____CO  ____Fe + ____CO2

14. Balancing Equations Practice
___(NH4)3PO4 + ___ Pb(NO3)4 ___Pb3(PO4)4 + ___NH4NO3