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Unit 11 Chemical Equations and Law of Conservation of Mass

Unit 11 Chemical Equations and Law of Conservation of Mass. Consider the two representations of reactions below. X. Y. Which of the two models (X or Y) represent a physical change, and which one represents a chemical change? Explain your choices. Formation of Solutions ( d issolving).

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Unit 11 Chemical Equations and Law of Conservation of Mass

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  1. Unit 11Chemical Equations and Law of Conservation of Mass

  2. Consider the two representations of reactions below. X Y Which of the two models (X or Y) represent a physical change, and which one represents a chemical change? Explain your choices.

  3. Formation of Solutions (dissolving) • It can be an endothermic or exothermic process. • Is it a chemical reaction?

  4. Formation of Solutions (dissolving) Covalent molecules … • DO NOT break apart when dissolved. • When they dissolve, it is a physical change. Ionic Compounds… • DO break apart when dissolved. • When they dissolve, it is a chemical change.

  5. Covalent molecules dissolving

  6. covalent ionic

  7. Chemical Equations What does a chemical equation represent? www.middleschoolchemistry.com www.elmhurst.edu

  8. Chemical Equations Your turn - Write the chemical equation that represents the following: N H H H H H N N H H H H H H N H www.middleschoolchemistry.com ______ + ______  _______ 3H2+N22NH3 www.whatsinsidescjohnson.com

  9. Chemical Equations Your turn - Write the chemical equation that represents the following: www.middleschoolchemistry.com ___+___ ____ O2+2Fe2FeO Fe Fe www.painetworks.com O O O O Fe Fe www.elmhurst.edu

  10. Chemical Equations • Chemical equations describe a chemical reaction • All chemical equations have reactants and products. Reactants  Products • The arrow indicates “yields” or “produces” but not equals. • The numbers in the front of the chemical formulas are called stoichiometric coefficients.

  11. Chemical Equation Symbols

  12. Chemical Equations For example: 12H2O(l)+6CO2(g) C6H12O6(s)+12O2(g) Reads as… 12 molecules ofliquid water plus 6 molecules ofgaseous carbon dioxide yields 1 molecule ofsolid sugar (glucose) and 12 molecules ofoxygen gas.

  13. Chemical Equations For example: 12H2O(l)+6CO2(g) C6H12O6(s)+12O2(g) Also reads as… 12 moles ofliquid water plus 6 moles ofgaseous carbon dioxide yields 1 mole ofsolid sugar (glucose) and 12 moles ofoxygen gas.

  14. Chemical Equations Express the chemical equation below in words: 2H2O(l)+2Na(s)2NaOH(aq)+ H2(g)

  15. Chemical Equations Practice: Express the chemical equations below in words: NaCl(s)+ AgNO3(aq)AgCl(s)+ NaNO3(aq) 2K2O(s)+2H2O(l)4KOH(aq)

  16. Law of Conservation of Mass Why do the substances in a chemical reaction have coefficients? e.g. 2H2 + O2 2H2O “Matter cannot be created or destroyed, it can only change forms.” Chemical reactions follow the law of conservation of mass, meaning - same atoms in the reactants and products; no new elements made - same number of atoms on the reactants and products; no atoms lost or new atoms produced - mass of reactants equal the mass of products

  17. H H H H H H O O Law of Conservation of Mass A balanced chemical equation follows the law of conservation of mass: e.g. 2H2(g) + O2(g) 2H2O(l) Check: H H O O 4.0 grams 4 atoms 2 atoms 32 grams 4.0 grams 4 atoms 2 atoms 32 grams

  18. Law of Conservation of Mass Complete the table to check if this chemical equation follows the law of conservation of mass: 2Na(s) + O2(g) Na2O(s) 46.0 grams 32 grams 2 atoms 2 atoms 46.0 grams 2 atoms 1 atom 16 grams

  19. Law of Conservation of Mass Given the balanced chemical equation below, find the mass of glucose, C6H12O6. 6CO2(g) + 6H2O(l) C6H12O6(s) + 6O2(g) ? g/mol 264 g 192 g 108 g 180 g

  20. Law of Conservation of Mass Given the balanced chemical equation below, find the mass of lead (II) iodide, PbI2. 2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) + PbI2(s) 461 g 332 g 331 g 202 g ?

  21. Balancing Chemical Equation Practice: Is this chemical equation balanced? LiCl(aq) + Pb(NO3)2(aq) LiNO3(aq) + PbCl2(s) 2 atoms 6 atoms 1 atom 1 atom 1 atom 2 atoms 3 atoms 1 atom 1 atom 1 atom

  22. Balancing Chemical Equation Practice: Which of the following chemical equations obeys the Law of Conservation of Mass? • N2 (g) + 2O2(g) N2O4(g) b. CH4(g) + O2(g)  CO2(g) + H2O(g) c. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)

  23. Subscripts vs Coefficients web.arc.losrios.edu

  24. Balancing Chemical Equation How do you balance chemical reactions? • - You may add coefficients in front of the compounds to balance the reaction • - You may notchange the subscripts.

  25. Balancing Chemical Equation Balance the chemical equation below. Hydrogen sulfide reacts with barium chloride producing hydrochloric acid and barium sulfide. H2S + BaCl2 HCl + BaS Reactants: Products: H – 2 atoms H – 1 atom S – 1 atom S – 1 atom Ba – 1 atom Ba – 1 atom Cl – 2 atoms Cl – 1 atom 2 2 atoms NOT BALANCED 2 atoms

  26. Balancing Chemical Equation Balance the chemical equation below. Methane burns in oxygen gas forming carbon dioxide and water vapor. CH4 + O2 CO2 + H2O Reactants: Products: C – 1 atom C – 1 atom H – 4 atoms H – 2 atom O – 2 atoms O – 3 atom 2 2 NOT BALANCED 4 atoms 4 atoms 4 atoms

  27. Balancing Chemical Equation Balance the chemical equation below. Carbon disulfide reacts with copper(II) chloride forming copper (II) sulfide and carbon tetrachloride. CS2 + CuCl2 CuS + CCl4 Reactants: Products: C – 1 atom C – 1 atom S – 2 atoms S – 1 atom Cu– 1 atoms Cu – 1 atom Cl– 2 atoms Cl – 4 atoms 2 2 2 atoms 2 atoms 2 atoms 4 atoms

  28. Balancing Chemical Equation Practice: Balance the chemical equations. • Al + O2 Al2O3 • Ca + H2O  Ca(OH)2 + H2 • HI + Hg(NO3)2 HNO3 + HgI2 4Al + 3O2 2Al2O3 Ca + 2H2O  Ca(OH)2 + H2 2HI + Hg(NO3)2 2HNO3 + HgI2

  29. Types of Reactions • Combination/Synthesis/Composition A + B  AB • Decomposition AB  A + B • Single Replacement C+ AB  AC + B • Double Replacement AB + CD AD + CB • Combustion CxHy+ O2CO2+ H2O • Redox – any of the above where the oxidation number of two species changes +

  30. synthesis • Also known as composition or synthesis; one product ___K (s) +___Br2 (l)  ___KBr (s) http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm

  31. synthesis ____Zn (s) + ___I2 (l)____ ZnI2 (s) http://genchem.chem.wisc.edu/demonstrations/Gen_Chem_Pages/04chemrxnpage/chemicalreactions.htm

  32. Decomposition • Single reactant breaks down into two or more simpler substances

  33. Single Replacement • A single element replaces another element in a compound. • Must use activity series to determine if reaction will take place. More active will replace less active. ___Cu (s)+ __AgNO3 (aq)  __Cu(NO3 )2 (aq)+ ___Ag (s) Remember: -Metal can only replace metal(or hydrogen) -Nonmetal can only replacenonmetal SR animation

  34. Using the activity series: Determine if the element by itself is a metal or a nonmetal. • If it is a metal, circle the metal in the compound. • Then, look on the activity series (on back of EOC periodic table): • If metal by itself is higher (more active) than the metal you circled, then it WILL replace the other metal and the REACTION WILL TAKE PLACE. • If metal by itself is lower (less active) than the metal you circled, then it WILL NOT replace the other metal and NO REACTION WILL OCCUR. • If it is a nonmetal, circle the nonmetal in the compound. • Then, look on the periodic table. Remember, fluorine is the most active nonmetal. • If nonmetal by itself is more active than the nonmetal you circled, then it WILL replace the other nonmetal and the REACTION WILL TAKE PLACE. • If nonmetal by itself is less active than the nonmetal you circled, then it WILL NOT replace the other nonmetal and NO REACTION WILL OCCUR.

  35. Double ReplacementClue: Do-See-DohAB + CD  AD + CB

  36. Double Replacement • Two reacting compounds, with metals trading places. • A precipitate (insoluble solid) is formed. ___AgNO3 (aq)+ ____NaCl (s)  ____NaNO3 (aq)+ ____AgCl (s)

  37. Determining solubility of products • Use the solubility rules on the back of the periodic table. • The solubility rules are organized by the anion in the compound. • Find the anion. * this is the negative ion * • Determine if, based on the cation, the compound is soluble (aq) or insoluble (s) in water. • Write the (aq) or (s) after the compound • Practice: • AgCl • K(NO3) • PbS

  38. Solubility Shortcuts – here’s all you need to remember: • All group 1 metals • All nitrates (NO3- ) • All acetates (C2H3O2- ) • All ammonium (NH4+) ARE ALWAYS SOLUBLE (aq) Remember HAP Stands for Mercury (Hg), Silver (Ag) and Lead (Pb) Compounds with these elements are usually INSOLUBLE (s)

  39. Try these: NaC2H3O2 Hg(OH)2 MgBr2 (NH4)2SO4

  40. _C3H8 + _O2 _ CO2 + _H2O + energy A combustion reaction is when oxygen combines with another compound to form water and carbon dioxide. It is highly exothermic Combustion .

  41. OXIDATION-REDUCTION REACTIONS • a reaction where electrons are transferred between reactants and products

  42. OXIDATION-REDUCTION REACTIONS a. Loss of Electrons is OXIDATION • oxidation number increases across the arrow. • Gain of Electrons is REDUCTION • oxidation number decreases across the arrow. *LEO the Lion Says GER These must occur together. Can’t have one without the other.

  43. OXIDATION-REDUCTION REACTIONS Oxidation Number (Oxidation State) • a method of keeping track of electrons gained (reduced) and lost (oxidized).

  44. OXIDATION-REDUCTION REACTIONS Rules for assigning oxidation numbers a. Atoms in their elemental form have an oxidation number of zero. Cu = 0 b. Monatomic ions have an oxidation number equal to their charge. K+1= +1. c. Nonmetals have negative oxidation numbers. i. Oxygen is -2 in all compounds with the exceptions of peroxides in which it is -1 ii. Hydrogen is usually +1 with nonmetals Hydrogen is usually -1 with metals d. The sum of the oxidation number in an neutral compound is zero.

  45. OXIDATION-REDUCTION REACTIONS How to identify a redox reaction. a. Determine the oxidation number of each element in each compound. b. Compare the reactants and products. • If there is a change in the oxidation number of any species, then it is redox. • Number increases across arrow = oxidation LEO • Number decreases across arrow = reduction GER

  46. OXIDATION-REDUCTION REACTIONS Practice- are the following redox reactions? ______ a. NaCl + AgNO3 --> NaNO3 +AgCl ______ b. FeCl2 + Cl2 FeCl3

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