1. Chemical Reactions
Chapter 4.1–4.2 & Ch 5.1–5.3

2. Chemical Reactions
Chemical Reaction: A process that transforms one set of chemical substances into another
When atoms break existing chemical bonds and form new ones
Evidence of a chemical reaction:
Change in properties (new substance, color)
Change in energy (temperature or light)

3. Chemical Reactions
Reactants are the chemicals present BEFORE the reaction
Products are the chemicals present AFTER the reaction

4. Chemical Equations Ex: CaCO3  CaO + CO2
Chemical Equations symbolize what happens during a reaction
like a math equation…with  instead of =
REACTANTS  PRODUCTS
Reactants and products are shown as chemical formulas
Ex: CaCO3  CaO + CO2
When limestone is heated, it changes into calcium oxide and carbon dioxide
Notice that the elements are the same before and after the reaction.
heat

5. CaCO3  CaO + CO2 Mass is Conserved
The same atoms that are present at the start of the reaction (reactants) are also there at the end (products).
CaCO3  CaO + CO2
1 calcium, 1 carbon, and 3 oxygen atoms
The atoms are simply rearranged

6. Mass is Conserved
Law of Conservation of Mass: The mass of the products will equal the mass of the reactants
Matter is neither created nor destroyed.
The atoms present in the reactants are the same atoms that form the products…they are just rearranged.

7. Controlling Reactions
Chemists can control the rate of a reaction by adjusting the temperature.
Increasing the temperature will speed up the reaction
Molecules are moving faster so they collide more frequently
Decreasing the temperature will slow down the reaction
Molecules are moving slower so they collide less frequently

8. Controlling Reactions
Chemists can also control the rate of a reaction by adjusting the:
Concentration –amount of a substance in the reaction
Higher concentration  bigger/faster reaction
Surface Area – amount of surface exposed to the reaction
Greater surface area  faster reaction
Catalysts and Inhibitors – chemicals that speed up or slow down the reaction
Catalysts – speed up the reaction or cause it to happen
Inhibitors – slow down the reaction or cause it to stop