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CHEMICAL REACTIONS

CHEMICAL REACTIONS. CHEMICAL EQUATIONS. magnesium + chlorine magnesium chloride. El Camino College Chemistry 21A Dr. Dragan Marinkovic. CHEMICAL REACTIONS.

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CHEMICAL REACTIONS

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  1. CHEMICAL REACTIONS CHEMICAL EQUATIONS magnesium + chlorine magnesium chloride El Camino College Chemistry 21A Dr. Dragan Marinkovic

  2. CHEMICAL REACTIONS CHEMICAL EQUATIONS magnesium + chlorinemagnesium chloride Mg(s) + Cl2 (g)MgCl2(s) REACTANTS PRODUCTS BALANCED EQUATION The Law of Conservation of Matter: atoms are neither created nor destroyed in chemical reactions. (atoms are conserved, but molecules are NOT) (s) = solid; (l) = liquid; (g) = gas/gaseous; (aq) = aqueous aqueous (from Latin “aqua” = water) = dissolved in water El Camino College Chemistry 21A Dr. Dragan Marinkovic

  3. CHEMICAL REACTIONS CHEMICAL REACTIONS NONREDOX REDOX COMBINATION DOUBLE REPLACEMENT (METATHESIS) DECOMPOSITION COMBINATION SINGLE REPLACEMENT (SUBSTITUTION) DECOMPOSITION El Camino College Chemistry 21A Dr. Dragan Marinkovic

  4. CHEMICAL REACTIONS REDOX REACTIONS • OXIDATION REACTIONS • (originally) reactions with oxygen • nowadays: • - process of giving up electrons • (increase of positive charge, i.e./or • decrease in negative charge) = • an oxydation number increase • loss of hydrogen • REDUCTION REACTIONS • (originally) process in which • oxygen was lost • nowadays: • - process of gaining electrons • (increase of negativecharge, i.e./or • decrease in positive charge) = • an oxydation number decrease During ANY redox reaction electrons are exchanged between atoms and/or ions; some are oxidized others are reduced. rusty iron fire El Camino College Chemistry 21A Dr. Dragan Marinkovic

  5. CHEMICAL REACTIONS REDOX REACTIONS Na Na+ + e- Cl + e- Cl- Na + Cl Na+Cl- OXIDIZED Mg Mg2+ + 2e- O + 2e- O2- Mg + O Mg2+O2- REDUCED Ca Ca2+ + 2e- 2F + 2e- 2F- Ca + 2F Ca2+F2- El Camino College Chemistry 21A Dr. Dragan Marinkovic

  6. CHEMICAL REACTIONS REDOX REACTIONS Na Na+ + e- Cl + e- Cl- Na + Cl Na+Cl- OXIDATION NUMBERS = O.N. (OXIDATION STATES) Positive or negative numbers assigned to the elements in chemical formulas according to specific set of rules. OXIDIZED Mg Mg2+ + 2e- O + 2e- O2- Mg + O Mg2+O2- REDUCED elements: O.N. = 0 Ia group: O.N. = +1 Iia group: O.N. = +2 hydrogen: O.N. = +1 oxygen: O.N. = -2 O (in peroxides only): O.N. = -1 sum of all atoms in a compound O.N. = 0 sum of all atoms in polyatomic ion O.N. = ion charge Ca Ca2+ + 2e- 2F + 2e- 2F2- Ca + 2F Ca2+F2- El Camino College Chemistry 21A Dr. Dragan Marinkovic

  7. CHEMICAL REACTIONS REDOX REACTIONS Areducing agent(also called areductantor reducer) is the element or compound thatreduces another species. In doing so, itbecomes oxidized, and is therefore theelectron donor. Anoxidizing agent(also called anoxidant, oxidizer) can be defined as either achemical compoundthatreadily transfers oxygen atoms, or a substance that gains electrons. REMEMBER: electron transferstake place ONLY during formation of ionic compounds. In covalent substances the ELECTRONS ARE SHARED. We just, by arbitrary practice ASSIGN SHARED ELECTRONS to the more electronegative element sharing them. None of the atoms in a covalent molecule acquire a net charge. El Camino College Chemistry 21A Dr. Dragan Marinkovic

  8. CHEMICAL REACTIONS DECOMPOSITION REACTIONS DECOMPOSITION REACTION: A single substance reacts to form two or more simpler substances. 2H2O2    2H2O + O2(g) 2HgO(s) 2Hg(l) + O2(g) Montroydite Aragonite Calcite Vaterite or (μ-CaCO3) Chalk Limestone Marble Travertine CaCO3(s) CaO (s) + CO2(g) 500 milligram calcium supplements made from calcium carbonate El Camino College Chemistry 21A Dr. Dragan Marinkovic

  9. CHEMICAL REACTIONS COMBINATION REACTIONS : (ADDITION or SYNTHESIS Rxns) Two or more substances react to form a single substance. REPLACEMENT REACTIONS : SINGLE REPLACEMENT REACTION An element reacts with a compound and displaces another element from the compound. S (s) + O2 (g) --> SO2 (g) 2SO2(g) + O2 (g) --> 2SO3 (g) SO3(g) + H2O (l) --> H2SO4 (aq) 2000 United States chemical industry CHEMICAL 2000 PRODUCTION PRODUCTION RANK (in 109 kg) 1 Sulfuric acid 39.62 2 Ethylene 25.15 3 Lime 20.12 4 Phosphoric acid 16.16 5 Ammonia 15.03 6 Propylene 14.45 7 Chlorine 12.01 8 Sodium hydroxide 10.99 DOUBLE REPLACEMENT REACTION Two compounds react and exchange partners to form two new compounds. AgNO3(aq) + KCl(aq) ‑‑‑‑> AgCl(s) + KNO3(aq) El Camino College Chemistry 21A Dr. Dragan Marinkovic

  10. CHEMICAL REACTIONS IONIC REACTIONS Many chemical reactions take place in water. Ionic compounds and some polar covalent compounds DISSOCIATE (break apart) INTO IONS when dissolved in water. MOLECULAR EQUATION 2KI + Pb(NO3)2 --> 2KNO3 + PbI2(s) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) NEUTRALIZATION REACTION TOTAL IONIC EQUATION 2K+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) --> 2K+(aq) + 2NO3-(aq) + PbI2(s) H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq) → Na+(aq) + Cl−(aq) + H2O(l) NET IONIC EQUATION NEUTRALIZATION REACTION 2I-(aq) + Pb2+(aq) --> PbI2(s) H+(aq) + OH−(aq) → H2O(l) SPECTATOR IONS Cl−(aq), Na+(aq) 2K+(aq), 2NO3-(aq) El Camino College Chemistry 21A Dr. Dragan Marinkovic

  11. CHEMICAL REACTIONS ENERGY and REACTIONS A + B C + D +/- E (energy) E (energy) released (+) or absorbed (-): heat, light, electricity, motion, high energy chemical bonds HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) + energy HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)∆H = 13.36 kcalmol-1 NEUTRALIZATION REACTION EXOTHERMIC REACTION (heat release) H+(aq) + OH−(aq) → H2O(l)∆H = 13.36 kcalmol-1 ENDOTHERMIC REACTION (heat absorption) ("cold-packs.") C3H8 + 5O2 ---> 4H2O + 3CO2 + energypropane + oxygen  water + carbon dioxide + energy Combustion reaction heat, light El Camino College Chemistry 21A Dr. Dragan Marinkovic

  12. CHEMICAL REACTIONS The MOLE and CHEMICAL EQUILIBRIUM El Camino College Chemistry 21A Dr. Dragan Marinkovic

  13. CHEMICAL REACTIONS The MOLE and CHEMICAL EQUATIONS Stoichiometry is the calculation of quantitative (measurable) relationships of the reactants and products in a balanced chemical reaction (chemicals). C3H8(g) + 5O2(g) ---> 4H2O(l) + 3CO2(g) Stoichiometry is the mass relationship in chemical reactions. (the math behind chemistry) El Camino College Chemistry 21A Dr. Dragan Marinkovic

  14. CHEMICAL REACTIONS The MOLE and CHEMICAL EQUATIONS Stoichiometry is the calculation of quantitative (measurable) relationships of the reactants and products in a balanced chemical reaction (chemicals). C3H8(g) + 5O2(g) ---> 4H2O(l) + 3CO2(g) 1 mol C3H8 + 5 mol O2 ---> 4 mol H2O + 3 mol CO2 Stoichiometry is the mass relationship in chemical reactions. (the math behind chemistry) 44 g C3H8 + 160 g O2 ---> 72 g H2O + 132 g CO2 How many moles and grams of water and carbon dioxide will be obtained if 11 g of propane was burned? 11 g Moles of C3H8 = ------------ = 0.25 44 g Moles of H2O = 4 x 0.25 = 1.00 gH2O = 1.00 x 18.0 = 18 g Moles of CO2 = 3 x 0.25 = 0.75 gCO2 = 0.75 x 44.0 = 33.0 g El Camino College Chemistry 21A Dr. Dragan Marinkovic

  15. CHEMICAL REACTIONS The LIMITING REACTANT LIMITING REACTANT The reactant present in a reaction in the least amount , based on its reaction coefficients and molecular weight. The reactant that determines maximum amount of product that can be formed. C3H8 + 5O2 ---> 4H2O + 3CO2propane oxygen (air) Propane tank N2(g) + 2O2(g) 2NO2(g) REACTANT IN EXCESS is the reactant that is not completely used up during the chemical reaction, that is, there is some of this reactant left over. 1.5 mol 50.0 g ? 1. Limiting reagent? 2. Maximum g NO2 produced? 1.5 mol N2 = 3 mol O2 LIMITING REACTANT PRINCIPLE The maximum amount of product possible from a reaction is determined by the amount of reactant present in the least amount, based on its reaction coefficients and molecular weight. 3 mol O2 = 48 g, hence N2 is limiting agent. 1.5 mol N2 = 3 mol NO2 3 mol NO2 = 3 x 46.01g = 183.03 g El Camino College Chemistry 21A Dr. Dragan Marinkovic

  16. CHEMICAL REACTIONS REACTION YIELDS REACTION YIELD the amount of product obtained in a chemical reaction. Usually expressed in grams of product. However, depending on the scale of the reaction it could also be given in mg or kg THEORETICAL YIELD the calculated amount of product using the balanced chemical reaction. ACTUAL YIELD the (measured) weight in grams or the corresponding amount in moles (molar yield). ACTUAL YIELD % YIELD = ---------------------------- X100 PERCENTAGE YIELD the percentage of the theoretical amount of product actually produced in the reaction. THEORETICAL YIELD El Camino College Chemistry 21A Dr. Dragan Marinkovic

  17. CHEMICAL REACTIONS 2HgO(s) 2Hg(l) + O2(g) 7.22 g HgO used 5.90 g Hg collected REACTION YIELD % yield = ? 2 mol HgO gives 2 moles Hg 1 mol HgO gives 1 mol Hg HgO f.w. = 216.6 Hg f.w. = 200.6 7.22 g Moles HgO used = ------------- = 0.0333 216.6 g theoretical yield of Hg = 0.0333 x 200.6 g = (6.6867 g) 6.69 g 5.90 g percentage yield = ------------------ x 100 = 88.19% 6.69 g El Camino College Chemistry 21A Dr. Dragan Marinkovic

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