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Unit 5: Chemical Equations & Reactions
Chapters 8 and 13
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Chemical Reactions Chemical reaction – process by which one or more substances change into different substance(s). REACTANTS PRODUCTS Starting chemical(s) Ending chemical(s)
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FOUR INDICATIONS Temperature change (gets hot or cold)
Gas forms (bubbling or fizzing) Formation of precipitate (solid that is made by the reaction of two solutions) Color change
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Chemical Equations Chemical Equations – describe what is happening during a chemical reaction Chemical equations can be written or formulas can be used. Reactants on left, products on right (of arrow) “+” means and Use (s), (l), (g), or (aq) after formulas “” means forms **Aqueous means the chemical is dissolved in water (solution)
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Formula Equations H2 (g) + O2 (g) H2O (l)
Formula Equations – represents the reactants and products by their symbols and formulas. H2 (g) + O2 (g) H2O (l) Reactants Products
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Counting Atoms in a Formula
Subscripts only apply to the element directly in front of the number. HNO H, 1-N, 2-O Subscripts outside of ( ) need to be multiplied by everything inside the ( ). (Distributive property) Ca3(PO4) Ca, 2-P, 8-O What if I put a coefficient in front of the formulas? 2Al(C2H3O2) Al C 18-H 12-O
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Balancing Why? chemical reactions must obey the law of conservation of mass (matter) Mass is conserved (stays the same) during any physical or chemical change Matter is not created or destroyed
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Balancing How??? 1. Count the atoms of each element on both sides of arrow 2. Use coefficients in front of the formulas to balance the atoms 3. NEVER change a subscript! **no coefficient = understood as a one (1) 5H2O Coefficient subscript
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Balancing Example _____H2 (g) + _____O2 (g) _____H2O (l) ___CS2 + ___Cl2 ___CCl4 + ____S2Cl2
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More Balancing Examples
____ N2 (g) + ____ H2 (g) ____ NH3 (g) ___ Al(OH)3 + ___ PbBr2 ___ AlBr3 + ___ Pb(OH)2
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Word and Formula Equations
Word Equations – Uses names of reactants and products in the reaction Hydrogen + Oxygen Water Have to turn the names into chemical formulas in order to balance
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Review Writing Formulas
Acids (always start off with H) “hydro-” acids H+ balanced by an anion (NO OXYGEN) HCl – hydrochloric acid “non-hydro” acids H+ balanced by negative polyatomic ion “-ic acids” were “-ate ions” H2SO4 – sulfuric acid “-ous acids” were “-ite ions” HNO2 – nitrous acid
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Review Writing Formulas
Binary Covalent compounds (two nonmetals) Numeric prefixes are subscripts…DO NOT BALANCE CHARGES!!! Mono, di, tri, tetra, penta, hexa, hepta, octa, nona, deca Sulfur hexafluoride – SF6 dinitrogen monoxide – N2O
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Review Writing Formulas
Ionic compounds (+ and – charges need to be balanced) Metal + nonmetal or metal + polyatomic ion Look up charges and balance…positive and negatives add up to ZERO! Sodium oxide Na+ and O2- Na2O Calcium phosphate Ca2+ and PO43- Ca3(PO4)2 Iron (II) carbonate Fe2+ and CO32- FeCO3
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Correct symbols MEMORIZE THESE 7 DIATOMIC MOLECULES!! Hydrogen - H2
Oxygen - O2 Nitrogen - N2 Fluorine - F2 Chlorine - Cl2 Bromine - Br2 Iodine - I2 “7-up” or “I brought clay for our new house”
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Writing Equations Examples
Solid magnesium reacts with hydrochloric acid to produce hydrogen gas and magnesium chloride solution. Copper (II) sulfate solution reacts with sodium hydroxide solution to form solid copper (II) hydroxide and a solution of sodium sulfate.
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Chemical Reactions Law of Conservation of Mass MUST be obeyed…so equations must be balanced total mass of the reactants must = total mass of the products
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Types of Chemical Reactions
FIVE TYPES OF REACTIONS: Combustion Synthesis Decomposition Single Displacement Double Displacement
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COMBUSTION Hydrocarbon (CxHy) reacting with O2 to form CO2 and H2O
Burning - Gives off heat and light!! Basic format of reaction: CxHy + O2 CO2 + H2O EXAMPLE: CH4 (g) + 2O2 (g) CO2 (g) + 2H2O(l)
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SYNTHESIS Two or more chemicals react to form A SINGLE NEW SUBSTANCE
i.d. HINT = A + B AB 2K(g) + Cl2(g) 2KCl(s)
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**you have to know your 7 diatomic molecules (7-up)
DECOMPOSITION A SINGLE COMPOUND BREAKS DOWN into two or more simpler products. i.d. HINT = AB A + B 2HgO(s) 2Hg(l) + O2(g) 2HBr H2 + Br2 **you have to know your 7 diatomic molecules (7-up)
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Synthesis & Decomposition
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SINGLE-DISPLACEMENT An element replaces another element that is in a compound i.d. HINT: A + BY B + AY Zn + Cu(NO3)2 Cu + Zn(NO3)2 Cl KI I KCl
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Single Displacement
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DOUBLE-DISPLACEMENT LiOH + HCl H2O + LiCl
Two different ionic compounds (in solution) mix to form two new ionic compounds. Produces a precipitate (solid), gas (bubbles), or molecular compound (like water) i.d. HINT: AX + BY AY + BX LiOH + HCl H2O + LiCl
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Double Displacement
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Single Displacement continued
Metals replace metals (activity series) List of metals A metal can only replace another if it is ABOVE it on the series K + CuCl2 Cu + KCl
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Single Displacement continued
Halogens can replace other halogens Fluorine is most active, can replace any halogen Iodine is least active and can replace nothing, but can be replaced by everything. F2 + 2NaBr I2 + NaCl Most reactive Least reactive
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Solubility Solubility: the ability of a substance to dissolve in another substance Soluble means stays in solution = (aq) Insoluble means forms a precipitate = (s)
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Double Displacement Switch the positive ions in the compounds
Check solubility rules for precipitate (insoluble) Re-balance charges Balance equation Pb(NO3)2 + KI NaCl + AlI3
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