1. Chemical Reactions
Chemical Changes

2. Chemical Reaction – a reaction in which one or more substances are changed to new substances
Reactants – substances that are about to react
Products – new substances produced
Produce
Reactants
Products

3. Lavoisier and the Conservation of Mass
French chemist Antoine Lavoisier
the father of modern chemistry
established that the total mass of the products always equals the total mass of the reactants
explanation of the law of conservation of mass
first to describe a chemical reaction known as combustion

4. Law of Conservation of Mass
total starting mass of all reactants equals the total final mass of all products
mercury(II) oxide oxygen plus mercury
10.0 g = g g

5. Chemical Equation
uses chemical formulas and symbols to describe a chemical reaction and the product it produces

6. Coefficients – number’s which represent the number of units of each substance in a reaction
4 Al(s) + 3 O2 (g) → 2 Al2O3
Subscripts – numbers which represent the number of atoms in a molecule of a particular element

7. Balancing Chemical Equations
Balanced chemical equations have the same number of atoms of each element on both sides of the equation
When balancing chemical equations NEVER change the subscripts, instead change the coefficient in front of the compounds needing balanced.
4 Al(s) + 3 O2 (g) → 2 Al2O3

8. 4 Al(s) + 3 O2 (g) → 2 Al2O3

9. Steps to Balancing Chemical Equations
Step 1: Write a chemical equation for the reaction using formulas and symbols. Make sure reactants are on the left side and products are on the right.
Step 2: Count the atoms in reactants and products.
Step 3: Choose coefficients that balance the equation.
Hint – Generally, if there is an even number of an element on one side and an odd on the other side, place a 2 in front of compound containing odd number of atoms.
Step 4: Recheck the numbers of each atom on both sides of the equation and adjust coefficients if necessary.
Remember NEVER change subscripts.

10. __NaBr +__Cl2 → __NaCl + __Br2
Example:
__NaBr +__Cl2 → __NaCl + __Br2
Step 1:
Write a chemical equation for the reaction using formulas and symbols. Make sure reactants are on the left side and products are on the right.
__NaBr __Cl2 → __NaCl __Br2

11. __NaBr + __Cl2 → __NaCl + __Br2
Step 2:
Count the atoms in reactants and products.
__NaBr __Cl2 → __NaCl __Br2
 Na 1 Br 2 Cl  2

12. 2NaBr + 2Cl2 → 2NaCl + 1Br2 Na 1 Br 2 Cl 2 Step 3:
Choose coefficients that balance the equation.
2NaBr Cl2 → 2NaCl Br2
 Na 1 Br 2 Cl  2

13. 2NaBr + 1Cl2 → 2NaCl + 1Br2 Na 1 2 Br 2 Cl 2 Step 4:
Recheck the numbers of each atom on both sides of the equation and adjust coefficients if necessary.
2NaBr Cl2 → 2NaCl Br2
 Na
1 2 Br 2 Cl  2

14. Balance this equation:
MgCl2 + AgNO3 → Mg(NO3)2 + AgCl
NaOH + CaBr2 → Ca(OH)2 + NaBr
HCl is slowly added to aqueous Na2CO3 forming NaCl, H2O, and CO2. Write a balanced equation for this reaction.
Write the balanced equation for the reaction of hydrogen gas and oxygen gas that forms water.

15. Balance this equation:
MgCl2 + AgNO3 → Mg(NO3)2 + AgCl

16. Balance this equation:
MgCl2 + AgNO3 → Mg(NO3)2 + AgCl
NaOH + CaBr2 → Ca(OH)2 + NaBr

17. Balance this equation:
MgCl2 + AgNO3 → Mg(NO3)2 + AgCl
NaOH + CaBr2 → Ca(OH)2 + NaBr
HCl is slowly added to aqueous Na2CO3 forming NaCl, H2O, and CO2. Write a balanced equation for this reaction.

18. Balance this equation:
MgCl2 + AgNO3 → Mg(NO3)2 + AgCl
NaOH + CaBr2 → Ca(OH)2 + NaBr
HCl is slowly added to aqueous Na2CO3 forming NaCl, H2O, and CO2. Write a balanced equation for this reaction.
Write the balanced equation for the reaction of hydrogen gas and oxygen gas that forms water.

19. MgCl2 + 2 AgNO3 → Mg(NO3)2 + 2AgCl
2NaOH + CaBr2 → Ca(OH)2 + 2NaBr
2HCl + Na2CO3 → 2NaCl + H2O + CO2
2H2 + O2 → 2H2O