Notes – Chemical Changes Chem/HChem 2013 Assign # 20 pts

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 ReactantsProducts

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 color 3) Production of a gas 4)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- CO 2 H 2 O NaCl NaHCO 3 Fe 2 O 3 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. C 6 H 12 O 6 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- CO 2 = Carbon Dioxide H 2 O = Dihydrogen monoxide NaCl = Sodium Chloride NaHCO 3 = Sodium Bicarbonate Fe 2 O 3 = 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. C 6 H 12 O 6 = 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. N 2, O 2, Cl 2, H 2 Chemical Changes

Table Salt NaCl- Sodium Chloride Sugar - glucose Fe 2 O 3 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 reaction ReactantsProducts Original substances = What are produced What is used yields or = equals C + O 2 = CO 2 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 + Cl 2 = 2NaCl SodiumChlorineSodium Chloride (Salt) 2 Na 2 Cl2 Na 2 Cl Energy Release Exothermic - Gives off or releases energy (burning) ReactantsProduct + energy Endothermic – Absorbs energy ( ice pack, photosynthesis) Reactants + energy Product

Types of Reactions 1) Synthesis – One product from two reactants H 2 + O 2 = H 2 O 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 + O 2 Copper Oxide Copper + Oxygen

Types of Reactions 3) Displacement – Two reactants form two new products Single Displacement: Cu + Ag(NO 3 ) Ag + Cu(NO 3 ) 2 Copper + Silver Nitrate Silver + Copper Nitrate

Types of Reactions 3) Displacement – Two reactants form two new products Double Displacement: KI + Pb(NO 3 ) K(NO 3 ) + PbI 2 Potassium + Lead Nitrate Potassium Nitrate + Lead Iodide Iodide CH4 + O2 CO2 + H2O Carbon + Oxygen Carbon Dioxide + Hydrogen Oxide Hydride