

 What is a chemical reaction?
 Demos
 Chemical Reaction : is when a substance undergoes a chemical change to produce a new substance or substances
 7 different types of chemical reactions

 Chemical equations: are used to represent a chemical change/reaction
 Ex. 2 H
2
+ O
2
 2 H
2
O
 Reactants : are the substances that undergo chemical change (bonds broken) (ingredients)
 Products : are the new substances produced by the change (new bonds made) (cookies)

 Reading Chemical equations
 + sign = “reacts with”
  sign = “to produce”, yields
 Mole is an amount of a substance that contains 6.02X10
23 particles. So rather than using atoms, molecules or ions we use the MOLE
 Coefficient = # of moles

 Shoes come in pairs,
 Eggs in a dozen.
 Particles to chemists come in MOLES
 Particles can be atoms, molecules, or ions

 Law of conservation of mass : states that mass is neither created nor destroyed in a chemical reaction
 By ordinary means, we can’t make or destroy matter
 ONLY REARRANGE IT!!!!!!!!

 When writing chemical equations, the law of conservation of mass must be followed.
 We must have the same amount of each element on both sides of the equation

 Coefficients : are used to show proportions of reactants and products)
 PERFECT PRACTICE,
MAKES PERFECT!!!!!!

 2 H
2 (g)
+O
2 (g)
 2 H
2
O
(l)
 Coefficients represent the number of units of each substance in the reaction
 Subscripts represent the number of atoms in the molecule
 Symbols show the state of reactants
(s) solid, (aq) aqueous), (g) gas, (l) liquid

 Why are coefficients important?
 Chemists need to know how much of a reactant will produce a certain amount of a product.

 7 types of reactions
 Synthesis: is a reaction in which two or more substances react to form a more complex single substance
 A+B  C
 Ex. 2 Na + Cl
2
 2 NaCl

 Decomposition Reaction: is a reaction in which a compound breaks down into two or more simpler substances
 AB  A+B
 Ex. 2 H
2
0  2 H
2
+ O
2
 Compost pile, digesting food, electrolysis (breaking down H electricity)
2
O with

 Combustion Reaction: is reaction where a substance reacts rapidly with oxygen.
 Flammability or explosiveness
 Ex. CH
4
+ 2 O
2
 CO
2
+ 2 H
 Ex. Burning any type of fuel
2
O
 Usually produces CO
2
(greenhouse gas)

 Oxidation Reaction: are reactions where a substance reacts slowly with the oxygen in air or water
 Happens with metals
 “rust” or “tarnish”
 Ex. 2 Ca + O
2
 2 CaO

 Single Replacement Reaction: is a reaction where one element takes the place of another element
 A+BC  AC+B or D+BC  BD +C
 Cu + 2 AgNO
3
 2 Ag + Cu(NO
3
)
2

 Double Replacement: is a reaction where 2 elements replace each other
 AB+CD  AD+CB
 CaCO
3
+ 2 HCl  CaCl
2
+ H
2
CO
3

 What two Chemical reactions are
“opposites” of each other and why?
 Synthesis and decomposition; in synthesis multiple substances combine to form a new one, while decomposition a single substance breaks apart into multiple simpler substances

 Exothermic Reactions : are reactions that release energy into their surroundings
 Give off heat (exergonic)
 Ex. Combustion Reactions
 Ex. Burning fossil fuels

 Endothermic Reaction : is a reaction where heat energy is absorbed by its surroundings
 Ice absorbs heat to melt into water
 Gets colder (endergonic)
 Ex. Ice pack and decomposition of mercury

 Increasing Reaction Rate:
 1. Temperature
 2. Surface area
 3. Stirring
 4. Concentration of Reactants
 5. Catalyst: is a substance that affects reaction rate without being used up.

 How are chemical bonds involved in energy exchanges?
 Breaking bonds requires energy; forming bonds releases energy.