1. Chemical Reactions
Fireworks are a result of chemical reactions

2. Chemical Reactions
Chemical Reactions form new substances by breaking and making chemical bonds
Chemical reactions change the way the atoms are arranged

3. Difference between Physical and Chemical Changes
A change in the state
Solid to liquid
Liquid to gas
Gas to liquid
Atoms/molecules of the substances do not change
Chemical
Atoms/molecules broken down or combined to form new substances
Properties of new substances are different than properties of the substances that make them up

4. Reactants and Products
Reactants: present at the beginning of the reaction
Products: are the substances formed by the chemical reaction
Example burning natural gas
CH4 + 2O2 > CO2 +2H2O
Reactants > Products

5. Evidence of Chemical Reactions
Color Change
Formation of Precipitate (solid formed from two liquids)
Formation of gas
Temperature change: endothermic (temp down) exothermic (temp up)
Change in smell

6. Classification of Chemical Reactions
Synthesis: a new compound is formed by the combination of simpler reactants
Smog formed when nitrogen and oxygen combine
N2 +2O2 > 2 NO2
oceanworld.tamu.edu

7. Classification of Chemical Reactions
Decomposition: A reactant breaks down into simpler products (reverse of synthesis)
Water can be decomposed into hydrogen and oxygen
2 H2O > 2H2 +O2

8. Classification of Chemical Reactions
Combustion: One reactant is always oxygen and another reactant often contains carbon and hydrogen
Burning of methane
CH4 + 2O2 > CO2 +2H2O
earthguide.ucsd.edu

9. The Rates of Chemical Reactions can vary
Concentration: measures the number of particles present in a certain volume.
A high concentration of reactants means there is a large number of particles that can collide and react
Turning the valve on a gas stove increases the methane molecules that can combine with oxygen and results in a bigger flame and faster combustion reaction

10. The Rates of Chemical Reactions can vary
Surface Area: the exposed surface of a substance.
To increase reaction break a large piece of the material so that there is more surface area of the material
Increase surface area=Increase reaction rate

11. Temperature
Rate of reaction can be increased by an increase in temperature which increases how fast the particles are moving and increases the number of collisions
Remember the cold and hot water distribution of food coloring

12. Catalyst
Catalyst: is a substance that increases the rate of chemical reaction but is not consumed in the reaction
Enzymes are catalysts that are used by living things to cause a chemical reaction. Resulting in a new product being made and the catalyst not being changed.

13. The masses of reactants and products are equal
Law of conservation of mass: states that in a chemical reaction atoms are neither created nor destroyed. (Antoine Lavoisier)
All atoms present in the reactants are also present in the products

14. Chemical Equations Reactants > Products
Balancing Chemical Equations
Use conservation of mass to balance: atoms can not be created or destroyed.
Reactants = products
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15. Chemical equations CH4 + O2 > CO2 + H2O Balanced? No
Reactants: C=1, H=4, O=2
Products: C=1, H=2, O=3
H and O not equal
Use coefficients to balance equations
CH4 + 2O2 > CO2 + 2H2O
C=1, H=4, O=4 > C=1, H= 4, O=4
Equation is now balanced!

16. Chemical Reactions Involve Energy Changes
It takes energy to break chemical bonds. This energy is called bond energy.
students.ed.uiuc.edu

17. Exothermic Reactions
Exothermic reaction: energy is released and temp goes up…more energy is released when products are formed.
Space shuttle on take off: white clouds of water vapor are formed

18. Exothermic Reactions Exothermic reactions release energy!
Exothermic reactions release energy!
All common combustion reactions are exothermic
Fireflies release energy in the form of light as an exothermic reaction

19. Endothermic reactions
Endothermic reactions: produce a decrease in temperature because the bond energies of the reactants are greater than the bond energies of the products
All endothermic reactions absorb energy!
Alka Seltzer and water…temperature goes down.

20. Endothermic Reactions
Photosynthesis
(general formula)
6CO2 +6H2O > C6H12O6 +6O2
plants absorb energy from sunlight to turn carbon dioxide and water into oxygen and glucose (sugar).
Energy is stored in the glucose molecule to be used when needed.

21. Life and Industry depend on Chemical Reactions
Living things require chemical reactions
Respiration: living things get energy from glucose by respiration. (combustion of glucose)
Photosynthesis
6CO2 +6H2O + energy> C6H12O6 +6O2
Respiration
C6H12O6 +6O2 > 6CO2 +6H2O + energy
Respiration is the opposite of photosynthesis!