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