Chapter 4 Chemical Reactions

Conservation of Mass When a chemical reaction happens, atoms are not allowed to be created or destroyed. If we start with 4.2g of 
substances, we must end 
with 4.2g of substances. Law of Conservation of Mass – Law that states mass cannot be created in destroyed in ordinary chemical and physical changes.

Balanced Equation To make sure that all of the mass and the matter is conserved, 
equations need to be balanced. A balanced equation is one that has the same numbers and types of atoms on both the reactant side and the product side. O C O C C O O C C C O

Generally, the element symbol is placed in the middle column Balanced Equation To use a REP Table, each element 
must have a row of its own. Chemical Equation – a representation of a chemical that uses symbols to show the relationship between the reactants and the product O C Reactant Element Product C O Generally, the element symbol is placed in the middle column In the Reactant and Product columns, the number of atoms of each 
element are written. When each element has matching numbers in both Reactant and Product columns, the equation is balanced. Reactant – a substance or molecule that participates in a chemical reaction Product- the substance that forms in a chemical reaction

Balanced Equation O C Reactant Element Product 3 6 C O

Balanced Equation O C 3C + 2O3 3CO2 Reactant Element Product 3 6 C O

Balanced Equation Fe O Reactant Element Product 1 2 3 Fe O

Balanced Equation Fe O Reactant Element Product 4 6 Fe O

Does the following equation follow Conservation of Mass? 14 Does the following equation follow Conservation of Mass? [This object is a pull 

tab] Answer No Ca and C are not the same. Yes No Ca Br C Br

Does the following equation follow Conservation of Mass? 15 Does the following equation follow Conservation of Mass? [This object is a pull 

tab] Answer Yes Yes No Ca Br Br Ca

16 Does the following equation follow Conservation of Mass? [This object is a pull 

tab] Answer Yes Yes No 2Na + Cl2 2NaCl