Notes – Chemical Changes

Chem/HChem 2013

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Chemical Changes

• Chemical properties – The ability of a substance to undergo chemical change

• Chemical reaction – When one or more substances change into two or more substances– Reactant : Substance present

at the beginning of a reaction– Product: Substance produced

in the reaction

Reactants Products

• Chemical reactions - Entail the breaking and forming of chemical bonds, causing atoms to become rearranged into new substances.

Chemical Changes

Law of Conservation of Mass

• During a chemical reaction, the mass of the products is always equal to the mass of the reactants.

• Mass is neither created nor destroyed, only changed to a different form .

Chemical changes

• Evidence of chemical change:

1) Transfer of energy (warm or cold)

2) Change in color3) Production of a gas4) Formation of a

precipitate (solid from a liquid mixture)

Chemical Changes• Chemical symbols - The

letters in the international “chemical language” to represent atoms, elements, and compounds

• Periodic Table - organizes and displays all the known elements. It is a chemist’s most useful tool.

Chemical Changes• Chemical symbols - The

letters in the international “chemical language” to represent atoms, elements, and compounds

• Periodic Table - organizes and displays all the known elements. It is a chemist’s most useful tool.

• Chemical formula - Words in the language of chemistry are composed of letters from the periodic table. Each word represents a different chemical substance

• Abbreviated form of compound showing the element symbols and ratio of atoms

• Examples-CO2

H2ONaClNaHCO3

Fe2O3• Subscript - A number written

below the normal line of letters that indicates how many atoms of the element are in one unit of the substance.

C6H12O6

Chemical Changes

• Chemical formula - Words in the language of chemistry are composed of letters from the periodic table. Each word represents a different chemical substance

• Abbreviated form of compound showing the element symbols and ratio of atoms

• Examples-• CO2 = Carbon Dioxide• H2O = Dihydrogen monoxide• NaCl = Sodium ChlorideNaHCO3 = Sodium BicarbonateFe2O3 = Iron Oxide (rust)

• Subscript - A number written below the normal line of letters that indicates how many atoms of the element are in one unit of the substance.

C6H12O6 = Glucose

Chemical Changes

• Chemical formula - Words in the language of chemistry are composed of letters from the periodic table. Each word represents a different chemical substance

• Abbreviated form of compound showing the element symbols and ratio of atoms

• Subscript - A number written below the normal line of letters that indicates how many atoms of the element are in one unit of the substance.

• Diatomic molecules - A handful of elements that exist as two bonded atoms of the same element.

• N2, O2, Cl2 , H2

Chemical Changes

Table SaltNaCl- Sodium Chloride

Sugar - glucose

Fe2O3

Iron Oxide

Chemical equations

• Chemical sentences. They contain the chemical formulas and summarize the details of a particular chemical reaction.

Chemical Reactions and Equations

Chemical Equations - Show what takes place in chemical reactions . Matter and mass are the

same before and after a reactionReactants Products

Original substances = What are produced What is used yields or

= equals

C + O2 = CO2 one atom Carbon 1 molecule 1 molecule

or 2 atoms carbon dioxide oxygen

Total atoms/elements on the left = equals to total number of atoms/elements on the right

2Na + Cl2 = 2NaClSodium Chlorine Sodium Chloride (Salt)2 Na 2 Cl 2 Na 2 Cl

Energy ReleaseExothermic - Gives off or releases energy (burning)Reactants Product + energyEndothermic – Absorbs energy ( ice pack, photosynthesis)Reactants + energy Product

Types of Reactions

1) Synthesis – One product from two reactants

H2 + O2 = H2O Hydrogen + Oxygen = Water (Hydrogen oxide)

Polymerization - Smaller molecules join to form one large molecule.

Types of Reactions

2) Decomposition – Two or more products from one reactant

CuO Cu + O2Copper Oxide Copper + Oxygen

Types of Reactions

3) Displacement – Two reactants form two new products

Single Displacement:

Cu + Ag(NO3) Ag + Cu(NO3)2Copper + Silver Nitrate Silver + Copper Nitrate

Types of Reactions

3) Displacement – Two reactants form two new products

Double Displacement:

KI + Pb(NO3) K(NO3) + PbI2Potassium + Lead Nitrate Potassium Nitrate + Lead Iodide

Iodide

CH4 + O2 CO2 + H2OCarbon + Oxygen Carbon Dioxide + Hydrogen OxideHydride