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Review naming rules if you are rusty.
Ch 8 Problem set: p 290 #8, 10, 11, 15, 25, 26, 27, 35, 37 Good figures in the book to look at.... Hey, it’s January. Word on the street is that looking at illustrations, tables, & figures in the book is a good idea. Review naming rules if you are rusty.
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Chemical equations describe chemical reactions
8.1 Chemical Equations Chemical equations represent, with symbols and formulas, the reactants and products in a chemical reaction. Chemical equations describe chemical reactions Requirements for all chemical equations: must show all reactants and products formulas must be correct Law of Conservation of Mass must be satisfied (equation must be balanced) see reactants and products
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2NaCl(s) 2Na(s) + Cl2(g)
H Cl2 2 HCl Hydrogen molecule reacts with Chlorine molecule to yield 2 molecules of Hydrochloric acid Ex1:– decomposition of sodium chloride – start from scratch – use symbols, heat, etc. 2NaCl(s) 2Na(s) + Cl2(g) Ex2: NaCl(s) = solid sodium chloride NaCl(aq) = solution of sodium chloride (in water) H2O(l) - liquid water (not aqueous - redundant)
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ppt or ↓ = precipitate (solid - only found on products side)
other symbols to know: = one way reactions ↔ = reversible reaction (g) or ↑ = gas ΔH = heat cat = catalyst (a substance that speeds up a reaction without being used up in the reaction) ppt or ↓ = precipitate (solid - only found on products side) E:\student\ch08\sec01\vc05\hc608_01_v05fs.htm
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So, what does the chemical equation actually mean?? H2 + Cl2 2 HCl
In atoms: 2 atoms of hydrogen gas react with 2 atoms of chlorine gas to yield 2 atoms of hydrogen and 2 atoms of chlorine In molecules: 1 molecule of hydrogen gas reacts with 1 molecule of chlorine gas to produce 2 molecules of hydrochloric acid In molar mass: H = 2.0; Cl = 71.0; HCl = 73.0 Video Clip
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Balancing Chemical Equations A trial and error process
Balance 1 atom at a time Balance atoms that appear only 1X per side first Balance polyatomic ions as a whole unit Balance diatomic elements last Balance O and H last – if possible
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Ex: __2_Mg ____O2 + _2_MgO Mg | Mg 1 O | O 1 If this doesn’t succeed, try doubling everything (particularly with combustion). Balancing Equation Video Try W.S. 8-1…
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8.2 Types of Chemical Reactions
There are 5 types of chemical reactions Synthesis Decomposition Combustion Single Replacement Double Replacement remember - first you’ve got to find the right products, then you gotta balance
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1. Synthesis (Combination)
Needs energy to occur (usually heat) General Formula: A + B AB Synthesis Ba + S Mg + Cl2 Al + Cl2 Na + O2 BaS MgCl2 AlCl3 Na2O 2Al + 3Cl2 2AlCl3 4Na + O2 2Na2O
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2. Decomposition Needs energy to happen (heat or electricity)
General Formula: AB A + B Decomposition FeCl3 HgO MgSO4 · 7H2O Fe + Cl2 Hg + O2 2FeCl3 2Fe + 3Cl2 2HgO 2Hg + O2 MgSO4 + 7H2O
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3. Combustion The reaction of hydrocarbons and oxygen General Formula:
Combustion Reaction CxHy + O2 H2O + CO2 CH4 C3H8 C4H10 C2H5OH
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4. Single Replacement Takes place in aqueous solutions
Needs very little energy to happen 2 Types Positive Ions Switch General Formula: AB + M MB + A HI + Mg AlCl3 + Ca Ca + HOH 2 MgI2 + H2 3 2 3CaCl2 + 2Al 2 Ca(OH)2 + H2 Single Replacement Diagram
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General Formula: AB + X AX + B
- Negative Ions Switch General Formula: AB + X AX + B NaCl + F2 BaS + O2 NaF + Cl2 BaO + S
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5. Double Replacement FeCl3 + NaOH Double Replacement Picture
again - aqueous solution - little energy - usually forms one soluble ionic product (aka - aqueous) and either a ppt, water, or a gas that bubbles out of water General Formula: AB + CD CB + AD FeCl3 + NaOH H2SO4 + NaOH NH4Cl + NaOH Double Replacement Picture
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8.3 Activity Series of the Elements
hey, some reactions happen and some don’t - for synthesis, combustion, and decomposition, we will assume they all happen given sufficient activation energy ( Ea ) For single replacement, use the Activity Series! Ca + H2O yields Al + H2O yields Al + HI yields Cu + HI yields NaCl + F2 NaF + Cl2 →
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Any single element above an element in a compound will replace it.
Rules for the single replacement activity series: Any single element above an element in a compound will replace it. The top 6 elements react with water. Metals above H react with acids (molecules that start with H – not water). The nonmetal reactivity series is F> Cl > Br... Metal Reactivity Video
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For double replacement reactions, use a Solubility Table!
Rules for double replacement reactions using a solubility table: If one of the products formed is water, the reaction happens. If a gas is formed, the reaction happens. If an insoluble product forms (I or Ss), the reaction happens (actually a reaction may happen when two soluble products form, but it doesn’t go to completion and is not directly observable). **** refer to “ions in solution” lab
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Na2CrO4 + KCl NR (both products soluble)
examples from the lab - Na2CrO4 + KCl NR (both products soluble) FeCl3 + KOH Fe(OH)3(ppt) KCl(aq) Yes! The reaction happens! Note: precipitate symbols include (ppt), (s), and . HCl + NaOH
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Heavier stuff doesn’t dissolve well
NIB Solubility Trends Cations -very soluble - Na, K, ammonium -very insoluble- Ag, Pb, Hg, transitions Anions - very soluble - nitrate for monatomics- F>Cl>Br .... very insoluble - carbonate, hydroxide, phosphate, sulfate sulfides - decompose general trend - As size decreases, solubility increases OR Heavier stuff doesn’t dissolve well
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Showing Energy Changes in Equations
Endothermic – put in heat (left side of equation) A + B + heat C ΔH is positive Exothermic – releases heat (right side) - A + B C + heat ΔH is negative
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Some helpful notes on writing phases in chemical reactions
Metals are solids (except Hg) In SR and DR reactions reactants that are compounds are always aqueous In SR and DR reactions products that are compounds should have their phases identified using a solubility chart (aq. vs. ppt) In S and D reactions ionic compounds are always solid In C reactions, the water, CO2, and O2 are gases. The hydrocarbon is a gas but usually becomes a liquid at C=6 or higher Most other covalent compounds are gases Acids (chemicals starting with H) are aqueous
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