Notes 

Unit 4-2 p.33-80

Chemical Change- Matter changes into other substances with different chemical and physical properties

The Law of Conservation of Mass- States that the total mass before a chemical reaction is the same as the total mass after the chemical reaction

Chemical Reaction- When atoms of one or more substances rearrange to form one or more new substances

Chemical Potential Energy- Energy released when atoms form bonds

Endothermic Reactions- Chemical reactions where more energy is required to break the bonds of the reactants than is released when products form

Exothermic Reaction- When more energy is released when products form than is required to break the bonds in the reactants

Law of Conservation of Energy- States that even though energy is always transferring energy is not created and energy is not destroyed

Chemical Changes in Matter

Chemical reaction-

The result when one or more substances change at the molecular level.

Oxygen + Hydrogen à Water

O2 (g) + 2 H2 (g) à 2 H2O (l)

*Physical reaction-

The result when one or more substances change in appearance, but NOT at the molecular level.

Melting Ice   H2O (s) à  H2O (l)

Reactants-(Tail side of the arrow/yield sign)

The starting materials of a rx(reaction).

O2 (g) + 2 H2 (g) à 2 H2O (l)

Products-(Pointy side of the arrow/yield sign)

The new substances formed in a rx.

O2 (g) + 2 H2 (g) à 2 H2O (l)

*( à)  yield sign= This symbol indicates the direction of the reaction.

O2 (g) + 2 H2 (g) à 2 H2O (l)

Chemical Equation-

A written expression that tells a chemical reaction as symbols and numbers.

Coefficient- 

The # in front of the element or compound.(Must be a whole number.)   Ex.  3H2

*Subscript- 

The # to the bottom right of the element. (Must be a whole number.)   Ex.  3H2

Balanced chemical equation-

This results in the same number of atoms of each element on both sides of the equation.

*When balancing an equation ONLY CHANGE the COEFFICIENT !

Na (s) + Cl2(g) à  NaCl(aq)

*Start with the element that has a different subscript!*

2 Na (s) + Cl2(g) à 2 NaCl(aq)

     Types of reactions

A) Synthesis- two separate elements combine to form a compound.

H2 + Cl2 → HCl

H2 + Cl2 → 2HCl

Sally + Sam → Sally Sam

B) Decomposition- Results when a compound breaks apart to form two new elements.

NaCl →  Na + Cl2

2NaCl → 2 Na + Cl2

Jack Jill → Jack + Jill

C) Single Displacement- Results when one element replaces an element in a compound.

CaCl2 + Na → NaCl + Ca

CaCl2 + 2Na → 2NaCl + Ca

Jack Jill + Barry → Barry Jill + Jack

D)                        Double Displacement- Results when the cations and anions in the compounds switch positions.

KBr + CaO → K2O + CaBr2

2KBr + CaO → K2O + CaBr2

Brenda Brent + SallySam→ Sally Brent + BrendaSam

E)  Combustions- This results when both elements combine with oxygen.

ALWAYS BALANCE OXYGEN LAST!!!!!!

C2H4 + O2 → CO2 + H2O

C2H4 +3 O2 → 2CO2 + 2H2O

Chemical reactions usually give off visual signs.

*Bubbles, smoke, explosions, light, precipitate, or a new color is formed.

Precipitate=

An insoluble solid that comes out of this type of reaction.

*Diatomic Molecule-

Molecule composed of two atoms in the natural state.

Ex. H2, N2, O2, Br2, F2, Cl2 and I2

**Physical states/phases of Matter**

solid (s)

gas  (g)

liquid  (l)

aqueous (aq)-Dissolved in water

crystalline solid (c)-Solid with a crystal structure.

Oxidation-

Loss of electrons.     (The charge goes up.)

Reduction-

Gain of electrons. (The charge goes down.)

Oil Rig

Oxidizing   Is Losing        Reduction   Is Gaining               

Leo the lion says “Ger”.

Lose    Electrons   Oxidized    Gain   Electrons    Reduced           

Ex.  Al  +   Cl2  à AlCl3

Balance the equation.

Ex.  2 Al  +   3 Cl2  à 2 AlCl3

*If the element is NOT bonded(in a couple), the charge is zero.

Oxidized and Reduced are listed on the product side!(Yield sign points to it.)

Reducing agent and Oxidizing agent are on the reactant side!(Located on tail side of yield sign.)

       0       0       +3 -1

Ex.  2Al  + 3  Cl2  à  2AlCl3

(Label the atoms.)

       R.A.    O.A.          Ox. Red.

*Write on the top of the page!* The agents are on your tail and the arrow will stab the RED OX!

Exergonic reaction-

Chemical reactions that release energy

Exothermic reactions-

Energy(heat) is given off by the reaction

Endergonic reactions-

Chemical reaction that requires more energy to break bonds than is released when new ones are formed.

(Chemical reactions that absorb energy.)

Endothermic reaction-

Energy(heat) must be provided for the reaction, more energy is required to break bonds than to form new ones (Chemical reactions that absorb heat.)

Catalyst-

 A substance that speeds up a chemical reaction without itself being permanently changed. 

*Enzymes-

A catalyst that promotes chemical reactions in living organisms.

Inhibitor-

Any substance that slows down a reaction