1. Intro to Chemical Reactions
Physical vs. Chemical Changes
Chemical Reactions
Identifying a chemical Reaction
Symbolizing a Chemical Reaction
Balancing Chemical Equations
Energy in Chemical Reactions
Chemical Reactions in Life and Industry

2. Physical vs. Chemical Changes
Physical Changes
Changes the appearance of the substance but substance remains the same.
EXAMPLE- Tearing paper or wetting dirt
Chemical Changes
Changes substance into a new substance
EXAMPLE – Frying an egg or baking a cake.

3. Chemical Reactions
A chemical reaction is the process where the atoms in a substance are rearranged and bonded into a new substance.
Chemical reactions form new substances by breaking and making chemical bonds.
Chemical changes occur as a result of chemical reactions.

4. Identifying a Chemical Reaction
How can we tell if a chemical reaction is taking place?
Release (evolution) of heat
Absorption of heat
Emission of light
Formation of a solid (precipitate)
Formation of gas bubbles
Color change

5. Symbolizing Chemical Reactions
We can use chemical equations to represent a chemical reaction. An equation has four parts:
Reactants: starting materials
Products: materials produced from the reaction
Coefficients: numbers placed in front of a chemical formula
Arrow: Indicates the direction of the reaction. Always points to the product.

6. Parts of a Chemical Equation
Chemical Equation: CuCl2 + H2S  CuS + 2 HCl
Chemical Formulas: CuCl2, H2S, CuS, HCl
Reactants: CuCl2 + H2S
Products: CuS + 2 HCl
Arrow read as “yields”: 
Coefficients: numbers used to indicate number of molecules of a compound like the 2 in front of the HCl.

7. Balancing a Chemical Equation
When writing a chemical equation you must obey the law of conservation of mass. This means that each side of the chemical equation (reactant and product) must have the same number and type of elements. For example CuCl2 + H2S  CuS + 2 HCl
Reactants: 1Cu, 2Cl, 2H and 1S
Products: 1Cu, 1S, 2H, and 2Cl.

8. Balancing… (cont.) To balance a chemical equation:
Count the number of atoms of each element on both sides of the arrow.
Put in a coefficient to get the same number of atoms of an element on both sides of the arrow.
Repeat until all elements have the same number of atoms on both sides of the arrow.

9. Balance these Equations
NaHCO3  Na2CO3 + H2O + CO2
Cu + AgNO3  Cu(NO3)2 + Ag
NH3 + H2S  (NH4)2S
NH4Cl + Ca(OH)2  CaCl2 + NH4(OH)
NH4(OH)  NH3 + H2O
CH4 + O2  CO2 + H2O

10. Classifying Chemical Reactions
Chemical Reactions can be classified for easier understanding.
Synthesis: A + B  AB
Decomposition: AB  A + B
Combustion: A + O2  varies
Replacement: AX + B  A + BX
Double Displacement: AX + BY  AY + BX

11. Classify these Equations
NaHCO3  Na2CO3 + H2O + CO2
Cu + AgNO3  Cu(NO3)2 + Ag
NH3 + H2S  (NH4)2S
NH4Cl + Ca(OH)2  CaCl2 + NH4(OH)
NH4(OH)  NH3 + H2O
CH4 + O2  CO2 + H2O

12. Energy in Chemical Reactions
Energy for chemical reactions are stored in the bonds of the chemical in the form of bond energy.
Chemical reactions involve breaking bonds and forming new bonds.
Breaking bonds require/absorb energy
Forming bonds release energy.
If more energy is absorbed than released, the reaction is endothermic.
If more energy is released than absorbed, the reactions is exothermic.

13. Endothermic vs. Exothermic
Exothermic Reaction
Net release of energy
Products have more bond energy than reactants
releases heat or light.
Causes an increase in temperature of surroundings (gets hotter).
Endothermic Reaction
More energy absorbed
Reactants have more bond energy than products.
Light or heat absorbed
Causes a decrease in temperature of surrounding (gets colder).

14. Rates of Chemical Reactions Vary
Concentration: An increase in concentration of reactants increases the number of particles that can interact and speeds up a reaction.
Surface Area: An increase in surface area is made by decreasing the particle sizes allowing more interactions and speeding up a reaction.
Temperature: Adding energy raises the temperature and makes particles move faster and collide more frequently, speeding up a reaction.
Catalysts: chemicals added to a chemical reaction that speeds up a chemical reaction but are not changed in the reaction.

15. Chemical Reactions in Life and Industry
Living things require chemical reactions for energy: photosynthesis and respiration.
Chemical reactions are used in technology: energy in a battery, gasoline combustion, and catalytic converters.
Chemical reactions are used in industry to make useful products: silicon production for use in electronic devices.