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Chemical Reactions Unit

Chemical Reactions Unit. Balance and Write Chemical Equations Predict Products of Chemical Reactions. Overview. the core of chemistry – how chemicals react with one another. Overview. Two parts: 1. Language of chemical reactions a) formulas (words/vocabulary) – from last unit

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Chemical Reactions Unit

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  1. Chemical Reactions Unit Balance and Write Chemical Equations Predict Products of Chemical Reactions

  2. Overview • the core of chemistry – how chemicals react with one another

  3. Overview Two parts: 1. Language of chemical reactions a) formulas (words/vocabulary) – from last unit b) chemical equations (sentences)

  4. Language of chemical reactions: b) chemical equations Sequence: i) balance skeleton formula equations, ii) word equations  balanced formula equations, iii) Sentence descriptions  balanced formula equations iv) write complete, balanced formula equations to describe chemical reactions observed in lab or as demos

  5. Overview 2. Different types of reactions a) classify b) predict products c) acids and bases, pH

  6. Writing Chemical Equations Example: Iron and chlorine gas react to produce the salt iron(III) chloride. Word equation: describes the reaction in words, using equation symbols Iron(s) + chlorine(g)iron (III) chloride(s) Skeleton formula equation: describes the reaction using equation symbols and correct chemical formulas; unbalanced Fe(s) + Cl2(g)FeCl3(s)

  7. Writing Chemical Equations Balanced formula equation: coefficients are used to equalize numbers of each atom on each side of the reaction 2Fe(s)+ 3Cl2(g)2FeCl3(s) Iron atoms on left (2) iron atoms on right (2) Chlorine atoms on left (3 x 2 = 6) chlorine atoms on right (2 x 3 = 6)

  8. Writing Chemical Equations Total and net ionic equations:describe the reaction using equation symbols and chemical formulas, shown as ions if the compound is aqueous (dissolved in water) (10.3) later

  9. Steps for Writing and Balancing Chemical Equations • Write a word equation with the names for all reactants on the left and all products on the right: ReactantsProducts • Convert the word equation to a skeleton formula equation by writing the correct formulas for all reactants and products. Be sure that your formulas correctly represent the particles in the reaction! 3. Use coefficientsin front of formulas to balance the equation. Do NOT change the formulas! • Begin balancing with an element that occurs only once on each side of the arrow.

  10. Steps for Writing and Balancing Chemical Equations • Multiply coefficient x subscript to determine the # of atoms of a specific element in one "term" of the equation: e.g. 4 H2O molecules: 4 x 2= 8 H atoms 4x 1 = 4 O atoms • Balance one type of atomat a time. • Balance H and O last, especially for combustion reactions.

  11. Balancing Hints 8. Even/Odd rulee.g. Fe + O2 Fe2O3 Since the number of oxygen atoms on the left must always be even., start by making the number of oxygen atoms on the righteven, then balance the iron atoms. 4 Fe + 3 O22 Fe2O3

  12. Balancing Hints 9. Intact polyatomic ions Fe + Pb(C2H3O2)2Fe(C2H3O2)3+ Pb The acetate ion (C2H3O2) stays together as a group, so balance the ion as a group. 2 Fe + 3Pb(C2H3O2)22Fe(C2H3O2)3 + 3 Pb One reason it is useful to know your ions!

  13. Balancing Hints Combustion reactions We’ll focus on these at a later time. Honors – check these hints out – two questions on WS #2

  14. Chemical Equation Symbols “yields” indicates the products of the reaction Indicates a reversible reaction A reactant or product in aqueous solution (dissolved in water) A reactant or product in the liquid state A reactant or product in the solid state A reactant or product in the gaseous state Reactants are heated Pressure exceeding normal atmospheric pressure Temperature at which reaction is carried out Formula of catalyst used to alter the rate of the reaction

  15. Practice – identify errors For each of the following, explain why the equation is not properly balanced, then write the correctly balanced equation. 1. Mg(NO3)2(aq) + 2 K(s) Mg(s) + K2NO6(aq) 2. AlCl3(aq) + AgNO3(aq)AgCl(s) + Al(NO3)3(aq)

  16. Practice – identify errors For each of the following, explain why the equation is not properly balanced, then write the correctly balanced equation. 1. Mg(NO3)2(aq) + 2 K(s) Mg(s) + K2NO6(aq) Formula for KNO3 is not written correctly = 2 KNO3 2. AlCl3(aq) + AgNO3(aq)AgCl(s) + Al(NO3)3(aq) Needs balancing  1, 3, 3, 1

  17. Practice – Writing and Balancing Chemical Equations (p. 4) Write the word equation, skeleton formula equation, and balanced formula equation for each of the following reactions: • Solid magnesium metal and solid silver sulfide react to form solid magnesium sulfide and solid metallic silver.  2. Aqueous nitric acid and calcium hydroxide solutions react to form water and aqueous calcium nitrate For each write the Word equation: Skeleton formula equation: Balanced Formula equation:

  18. Practice - KEY • Solid magnesium metal and solid silver sulfide react to form solid magnesium sulfide and solid metallic silver. Word equation: magnesium(s) + silver sulfide(s)  magnesium sulfide(s) + silver(s) Skeleton formula equation: Mg(s) + Ag2S(s)  MgS(s) + Ag(s) Balanced Formula equation: Mg(s) + Ag2S(s)  MgS(s) + 2 Ag(s)

  19. Practice - KEY  2. Aqueous nitric acid and calcium hydroxide solutions react to form water and aqueous calcium nitrate Word equation: nitric acid(aq) + calcium hydroxide(aq)  water(l) + calcium nitrate(aq) Skeleton formula equation: HNO3(aq) + Ca(OH)2(aq)  H2O(l) + Ca(NO3)2(aq) Balanced Formula equation: 2 HNO3(aq) + Ca(OH)2(aq)  2 H2O(l) + Ca(NO3)2(aq)

  20. Warm Up (p. 5 – Wr & Bal Notes) 3. Aluminum metal reacts with oxygen in the air to form aluminum oxide • When solid mercury (II) sulfide is heated with oxygen, liquid mercury metal and gaseous sulfur dioxide are produced • Oxygen gas can be made by heating potassium chlorate in the presence of the catalyst manganese dioxide. Potassium chloride is left as a solid residue.

  21. Warm Up (p. 5 – Wr & Bal Notes) 3. Aluminum metal reacts with oxygen in the air to form aluminum oxide Aluminum(s) + oxygen(g)  aluminum oxide(s) Al(s) + O2(g) Al2O3(s) 4 Al(s) + 3 O2(g) 2 Al2O3(s)

  22. Warm Up (p. 5 – Wr & Bal Notes) D D D 4. When solid mercury (II) sulfide is heated with oxygen, liquid mercury metal and gaseous sulfur dioxide are produced mercury (II) sulfide(s) + oxygen(g) mercury(l) + sulfur dioxide(g) HgS(s) + O2(g)  Hg(l) + SO2(g) HgS(s) + O2(g)  Hg(l) + SO2(g)

  23. Warm Up (p. 5 – Wr & Bal Notes) D, MnO2 D, MnO2 D, MnO2 5. Oxygen gas can be made by heating potassium chlorate in the presence of the catalyst manganese dioxide. Potassium chloride is left as a solid residue. potassium chlorate(s)  potassium chloride(s) + oxygen(g) KClO3(s)  KCl(s) + O2(g) 2 KClO3(s)  2 KCl(s) + 3 O2(g)

  24. Intro to Chemical Reactions Lab Prepare lab notebook for this lab: • Read the first page of the instructions carefully before you begin Include: • Overall purpose • List of materials and flowchart for each of the 8 stations (recommendation is 1 station per page) – minimum of 4 for Th/F • Include safety information and notes to yourself in your flowchart – see Flinn Scientific catalog, first section, on lab benches • Check out the lab setups themselves • Note checklists for each station (in the instructions) – use these to help you prepare your lab notebook so that you can focus on the lab itself

  25. Intro to Chemical Reactions Lab Add the following info to your lab notebook • Splint test: flame goes out: carbon dioxide flame flares up: oxygen “pop” and flame goes out: hydrogen

  26. Intro to Chemical Reactions Lab Full lab gear – apron and goggles Complete the experiment – observations, reaction predictions, etc. at each station before you continue to another station When finished, begin working on WSs

  27. Solubility Chart - used to predict the state of matter of products in DR reactionsS = soluble = aqueous (aq); I = insoluble = solid (s) Aluminum acetate vs. aluminum hydroxide

  28. Warm up • Identify the reactants and products in the following word equations: • Water decomposes to produce hydrogen and oxygen gases. • Sodium chloride is produced when sodium metal reacts with chlorine gas.  • Methane gas reacts with oxygen gas to form carbon dioxide and water. • Briefly describe the differences between a, b and c (how the sentence is written) and how you identified the reactants and products.

  29. Warm up Write and balance the following reactions: 1. Aqueous solutions of silver nitrate and potassium iodide are mixed. Silver iodide and potassium nitrate are produced. Use your solubility chart to figure out which one is the precipitate. 2. When nitrogen dioxide is bubbled through water it produces nitric acid and nitrogen monoxide. What are the states of matter?

  30. Warm up Write and balance the following reactions: • Aqueous solutions of silver nitrate and potassium iodide are mixed. Silver iodide and potassium nitrate are produced. Use your solubility chart to figure out which one is the precipitate. silver nitrate(aq) + potassium iodide(aq)  silver iodide + potassium nitrate AgNO3(aq) + KI(aq)  AgI(s) + KNO3(aq)

  31. Warm up Write and balance the following reactions: 2. When nitrogen dioxide is bubbled through water it produces nitric acid and nitrogen monoxide. What are the states of matter of nitrogen dioxide, nitric acid and nitrogen monoxide? Nitrogen dioxide + water(l)  nitric acid + nitrogen monoxide Nitrogen dioxide(g) + water(l) nitric acid(aq) + nitrogen monoxide(g) NO2(g) + H2O(l)  HNO3(aq) + NO(g) 3 NO2(g) + H2O(l)  2 HNO3(aq) + NO(g)

  32. Evidence of a Chemical Reaction(Chemical Reactions notes) We can only know the products of a chemical reaction by carrying out the reaction in the laboratory, BUT, we can make general predictions about the products of a reaction based on “types” of chemical reactions.

  33. Types of Chemical Reactions(not all reactions fit these categories) • Synthesis (or Combination) • Decomposition • Single Replacement • Double Replacement (or Metathesis) • Combustion 6. Oxidation-Reduction (Redox) (Honors)

  34. Energy Changes in Chemical Reactions 1.Exothermic Reaction Releases energy (energy = one of the products) C(s) + O2(g)  CO2(g) + 393.5 kJ DH = -393.5 kJ

  35. Energy Changes in Chemical Reactions 1.Endothermic Reaction absorbs energy (energy = one of the reactants) CaCO3(s) + 176 kJ CaO(s) + CO2(g) DH = + 176 kJ

  36. Synthesis (combination) A + B → AB (one product) usually produces energy – exothermic Examples: metal + nonmetal (often oxygen) Cu + O2→Cu2O Cu + O2→CuO Na + Br2 →NaBr nonmetal + nonmetal N2 + O2→NO2 SO2 + O2→SO3 metal oxide + water base MgO + H2O→Mg(OH)2 nonmetal oxide + water acid CO2 + H2O→H2CO3 (Honors) (Honors)

  37. Synthesis reactions are usually Exothermic Releases energy (energy is a product) C(s) + O2(g) CO2(g) + 393.5 kJ ΔH = -393.5 kJ

  38. Decomposition D or 7 or light AB A + B (one reactant, > 1 product) usually requiresenergy - endothermic Examples Compound 2 elements Ag2OAg + O2 reactant 2 elements (electrolysis) H2OH2 + O2 Metal carbonatemetal oxide + carbon dioxide (Honors) MgCO3MgO + CO2 Acid nonmetal oxide + water (Honors) H2CO3CO2 + H2O 7

  39. Decomposition reactions are usually Endothermic Absorbs energy (energy is a reactant) CaCO3(s) + 176 kJ  CaO(s) + CO2(g) ΔH = +176 kJ

  40. Demonstration Electrolysis of Water • Record your observations in your notes.

  41. Warmup • Write balanced chemical equations for the following synthesis and decomposition chemical reactions. • Figure out what the states of matter should be at room temperature. • Predict products according to the type of reaction.

  42. Warmup Synthesis: 1. carbon + oxygen  2. gallium + oxygen  3. nitrogen + hydrogen  (H) 4. phosphorus (V) oxide + water  (H) 5. calcium oxide + water 

  43. Warmup Synthesis: • carbon + oxygen  C(s) + O2(g) CO2(g) or 2 C(s) + O2(g) 2 CO(g) • gallium + oxygen  4 Ga(s) + 3 O2(g) 2 Ga2O3(s) • nitrogen + hydrogen  N2(g) + 3 H2(g)  2 NH3(g)

  44. Warmup Honors Synthesis: (H) 4. phosphorus (V) oxide + water  P2O5(s) + 3 H2O(l)  2 H3PO4(aq) (H) 5. calcium oxide + water  CaO(s) + H2O(l)  Ca(OH)2(s)

  45. Warmup Decomposition: 1. sodium oxide  • aluminum chloride  (H) 3. calcium carbonate  (H) 4. potassium chlorate 

  46. Warmup Decomposition: • sodium oxide  2 Na2O(s)  4 Na(s) + O2(g) • aluminum chloride  2 AlCl3(s) 2 Al(s) + 3 Cl2(g) D D

  47. Warmup Decomposition: (H) 3. calcium carbonate  CaCO3(s)  CaO(s) + CO2(g) (H) 4. potassium chlorate  2 KClO3(s) 2 KCl(s) + 3 O2(g) D D

  48. Single Replacement A + BX → AX + B Use activity series to predict – higher replaces lower CationReplacement Metal replaces Metal Mg +SnCl2MgCl2 + Sn Metal replaces H in HOH (H2O) K+ HOHKOH + H2 Metal replaces H in an acid Fe +H2SO4FeSO4+ H2 Anionreplacement Halogenreplaces Halogen Br2+SrI2SrBr2+I2 (s) (aq) (aq) (s) (l) (aq) (aq) (s) (s) (l) (aq) (g) (s) (aq) (aq) (g)

  49. Activity Series (tt34, 10.2)Used to predict Single Replacement Reactions See your reference sheet

  50. Demonstration – Single Replacement Reaction • Use the activity series on your reference sheet to predict the products of the following reactions: • Cu(s) + AgNO3(aq) • Ag(s) + Cu(NO3)2(aq)  • During the demo, record your observations

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