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Chemical Reactions

Chemical Reactions. Natural Approach to Chemistry Chapter 10. Learning Objectives. Sections 10.1-3 Characterize types of chemical reactions (redox,acid-base, synthesis, and single and double replacement) Apply mole concept & conservation of mass to calculate quantities

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Chemical Reactions

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  1. Chemical Reactions Natural Approach to Chemistry Chapter 10

  2. Learning Objectives Sections 10.1-3 Characterize types of chemical reactions (redox,acid-base, synthesis, and single and double replacement) Apply mole concept & conservation of mass to calculate quantities Distinguish between endothermic and exothermic processes Sections 10.4 Evaluate costs & benefits of resources Discuss technological effects & impacts on environ- mental quality Discuss production and use of natural resources Create and interpret potential energy diagrams

  3. Be sure you know these terms: Parts of a chemical reaction Synthesis Decomposition Single displacement Double displacement Polymerization Precipitate Polymer, polymerization Exo- and endothermic Enthalpy of reaction/formation Energy barrier Photosynthesis Chemical engineering Biodegradable Hazardous substances Sustainable chemistry Green chemistry

  4. Chemical Reaction Assignments • 10.1 322/1-7,31,37,38,52 • 10.3 322/8-15,39-41,64,65 • 10.4 3.22/16-29,43-47,66-71

  5. A Chemical Equation • Represents with symbols and formulas, the identities and relative molecular or molar amounts of the reactants and products in a chemical reaction.

  6. Word Equation / Formula Equation Methane + oxygen --> carbon dioxide + water CH4(g) + 02(g) --> CO2(g) + H20(g) Reactants Products The above formula equation is not balanced.

  7. Chemical Reaction Indications • Production of energy as heat and/or light. • Production of a gas. • Formation of a precipitate – a solid produced as a result of a chemical reaction in solution. A precipitate separates from the solution. • A color change.

  8. Chemical Equation Requirements • The equation must represent known facts. • The formulas for the reactants and products must be written correctly. DO NOT change subscripts. • The law of conservation of mass must be satisfied. The number of atoms of each element must be the same on each side of the yield sign. After a formula is written correctly, place coefficients in front of a formula to show conservation of mass.

  9. Diatomic Molecules When writing a chemical equation including any of the above elements, they are shown as diatomic molecules as in column 3 above.

  10. Coefficients • When placed in front of a correctly written chemical formula, a coefficient multiplies the number of atoms of each element indicated in the formula • 2O2 means 4 O • 2H20 means 4 H and 2 O

  11. Practice Write word and balanced chemical equations for: solid calcium reacts with solid sulfur to produce solid calcium sulfide. Include symbols for physical states. Ca(s) + S(s) --> CaS(s) Balanced: 1 Ca on each side 1 S on each side

  12. Write word and balanced chemical equation for: Hydrogen gas reacts with fluorine gas to produce hydrogen fluoride gas. H2(g) + F2(g) --> HF(g) H2(g) + F2(g) --> 2HF(g) Solid aluminum metal reacts with aqueous zinc chloride to produce solid zinc metal and aqueous aluminum chloride. Al(s) + ZnCl2(aq) --> Zn(s) + AlCl3(aq) Al(s) + 3 ZnCl2(aq) --> Zn(s) + 2 AlCl3(aq) 2 Al(s) + 3 ZnCl2(aq) -->3 Zn(s) + 2 AlCl3(aq)

  13. Translate these chemical equations into sentences: CS2(l) + 3O2(g) --> CO2(g) + 2SO2(g) Liquid carbon disulfide reacts with oxygen gas to produce carbon dioxide gas and sulfur dioxide gas. NaCl(aq) + AgNO3(aq) --> NaNO3(aq) + AgCl(s) Aqueous solutions of sodium chloride and silver nitrate react to produce aqueous sodium nitrate and a precipitate of silver chloride.

  14. Write & Balance: Hydrazine, N2H4, reacts violently with oxygen to produce gaseous nitrogen and water. N2H4(l) + O2(g) --> N2(g) + H2O(l) Is it balanced? No. There are 4H on reactant side and 2H on product side and O is 2/1. N2H4(l) + O2(g) --> N2(g) + 2H2O(l) N: 2/2 H:4/4 O:2/2

  15. Chemical Equation Indications 1. Coefficients indicate relative amounts of reactants and products (proportions, molecules, moles, grams, ratios). H2(g) + Cl2(g) --> 2HCl(g) 1 molecule H2 : 1 molecule Cl2 : 2 molecules HCl 1 mole H2 : 1 mole Cl2 : 2 moles HCl

  16. Coefficients can be used to determine relative masses of reactants and products H2(g) + Cl2(g) --> 2HCl(g) 1mol H2 x 2.02g H2= 2.02 g H2 mol 1 mol Cl2 x 70.90 g Cl2 = 70.90 g Cl2 mol 2 mol HCl x 36.46 g HCl = 72.92 g HCl mol

  17. 3. The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reactions.

  18. Balancing Chemical Equations • Write equation. • Write correct chemical formulae for each compound. • Balance according to the Law of Conservation of Mass by adjusting coefficients. • Start with the element appearing in the fewest substances. Balance free elements last. • Count atoms to be sure the equation is balanced.

  19. Practice - Write word, formula, and balanced chemical equations for this reaction. • Magnesium and hydrochloric acid react to produce magnesium chloride and hydrogen. Word Equation: Magnesium + hydrochloric acid --> magnesium chloride + hydrogen Formula Equation: Mg(s) + HCl(aq) --> MgCl2(s) + H2(g) Adjust coeffs: Mg(s) + 2HCl(aq) --> MgCl2(s) + H2(g) Count atoms: Mg: 1/1 H:2/2 Cl:2/2

  20. Solid sodium combines with chlorine gas to produce solid sodium chloride. Sodium(s) + chlorine(g) --> sodium chloride Na(s) + Cl2(g) --> NaCl(s) Balance: Na(s) + Cl2(g) --> 2NaCl(s) 2Na(s) + Cl2(g) --> 2NaCl(s)

  21. Types of Chemical Reactions • Synthesis A + X --> AX • Decomposition AX --> A + X • Single-displacement A + BX --> AX + B • Double-displacement AX + BY --> AY + BX • Combustion – a substance combines with oxygen releasing energy as light and heat. • Acid + Base --> Salt + Water • Reduction/oxidation (Redox) – covered in a later chapter

  22. Activity Series – elements organized according to how they react Most active metals: Li react w/cold Co Do not react w/H20. Rb H20 & acids Ni React w/acids, repla- K replacing H2. Sn cing H2. React w/O2 Ba React w/O2 Pb forming oxides. Sr forming oxides H2 React w/O2, forming Ca Sb oxides Na Bi Mg react w/steam Cu Al (not cold H20) Hg Mn and acids, repla- Ag Fairly unreactive, Zn cing H2. React Pt forming oxides only Cr with O2 forming Au indirectly. Fe oxides Cd An element can replace any element placed below it BUT It cannot replace any element above it. Zn can replace Cu but Au cannot replace Mg

  23. Nonmetal activity series: Most active F Cl Br I

  24. Sample Problems – activity series 50oC Zn(s) + H2O(l) ---> No reaction, water must be 100oC (steam) at least. Sn(s) + O2(g) --> Yes, any metal more active than Ag will react w/O2 to form an oxide. (Sn is above Ag) 2Sn(s) + O2(g) --> 2SnO Cd(s) + Pb(NO3)2(aq) --> Yes, Cd is above Pb. Products: Cd(NO3)2 + Pb Cu(s) + HCl(aq) --> No, Cu is below H

  25. 1. Synthesis Reaction A + X --> AX Samples: Fe(s) + S(s) --> FeS(s) 2Mg(s) + O2(g) --> 2MgO(s) H20 + SO3 --> H2SO4

  26. Synthesis with Oxides (see handout for more information!!) CaO(s) + H2O(l) --> Ca(OH)2(s) Pollution: SO2(g) + H2O(l) --> H2SO3(aq) 2H2SO3(aq) + H20(l) --> 2H2SO4(aq) Oxides: CaO(s) +SO2(g) --> CaSO3(s)

  27. 2. Decomposition Reaction AX --> A + X H20(l) --------> 2H2(g) + O2(g) (electrolysis) 2HgO(s) ---> 2Hg(l) + O2(g) electricity D

  28. D Decomposition of Metal Oxide CaCO3 --->CaO + CO2 Decomp of Metal Hydroxide Ca(OH)2 ---> CaO + H2O Decomp of Metal Chlorate 2KClO3 ----> 2KCl + 3O2 Decomp of Acids H2CO3 --> CO2 + H2O (occurs at room temp) H2SO4 ---> SO3 + H2O D D MnO2 D

  29. 3. Single Displacement Reaction A + BX --> AX + B Or Y + BX --> BY + X 1. Fe + CuSO4 --> FeSO4 + Cu 2. Cu + 2AgN03 --> Cu(NO3)2 + 2Ag 3. CI2 + 2KI --> 2KCl + I2 How is 3. different from 1. or 2.? In 1.& 2. metals are being displaced. In 3. a halogen is being displaced.

  30. Hydrogen displaced by a metal: Mg + 2HCl --> H2 + MgCl2

  31. 4. Double-Displacement Reaction AX + BY --> AY + BX A,X,B, and Y in reactants are ions. AY and BX are ionic or molecular compounds. • Formation of a Precipitate 2KI(aq) + Pb(NO3)2(aq) --> PbI2(s)+ 2KNO3(aq)

  32. Formation of a Gas FeS(s) + 2HCl(aq) –> FeCl2(aq) + H2S(g) Formation of Water HCl(aq) + NaOH(aq) --> NaCl(aq) + H20(l)

  33. Combustion Reactions 2H2(g) + O2(g) --> 2H2O(g) C3H8(g) + 5O2(g) --> 3CO2(g) + 4H20(g) Other products are heat and light.

  34. Predicting Activity (use the activity series handout) Zn(s) + H20(l) --> ? No, not hot enough. Steam needed (100oC) Ca(s) + H2O(l) --> ? Yes, Ca is above H on the chart. The products are: Ca(OH)2 + H2 (g) Pt(s) + O2(g) --> ? No.

  35. Cd(s) + 2HBr(aq) --> Yes, Cd is above H. Products: CdBr + H2(g) Mg(s) + steam --> Yes, Products: Mg(OH)2 + H2(g)

  36. Activity Series Activity of metals:Activity of halogen nonmetals Li <--Most active metal F2 <-- Most active nonmetal Rb react w/cold Cl2 K H20 & acids Br2 Ba replacing H2. I2 Sr React w/O2 Ca forming oxides Na Mg react w/steam Al (not cold H20) Mn and acids, repla- Zn cing H2. React Cr with O2 forming Fe oxides Cd Co Do not react w/H20. Ni React w/acids, repla- Sn cing H2. React w/O2 Pb forming oxides. H2 Sb Bi React w/O2, forming Cu oxides Hg Ag Fairly unreactive, Pt forming oxides only Au indirectly.

  37. Solubility Chart

  38. There are three key components to a chemical reaction: Reactants Products Energy (in or out)

  39. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions

  40. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions Photosynthesis is an endothermic reaction: energy is absorbed

  41. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions Photosynthesis is an endothermic reaction: energy is absorbed Cellular respiration is an exothermic reaction: energy is released

  42. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions Chapter 9.3 Properties of Solutions

  43. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions Chapter 9.3 Properties of Solutions Energy is absorbed from the surroundings so the pack feels cold

  44. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions Chapter 9.3 Properties of Solutions Energy is released into the surroundings so the pack feels hot

  45. There are three key components to a chemical reaction: Reactants Products Energy (in or out) Chapter 4.2 Chemical Reactions Chapter 9.3 Properties of Solutions Change in enthalpy enthalpy:the amount of energy that is released or absorbed during a chemical reaction

  46. Reaction Exothermic Endothermic Energy is released is absorbed Enthalpy change (∆H, J/mole) is a negative number ∆H < 0 is a positive number ∆H > 0

  47. Chemical equation for the combustion of carbon: C(s) + O2(g) CO2(g) ∆H = –393.5 kJ Reactants Products Energy thermochemical equation: the equation that gives the chemical reaction and the energy information of the reaction.

  48. Enthalpy calculations Chemical equation for the combustion of carbon: C(s) + O2(g) CO2(g) ∆H = –393.5 kJ The reverse chemical reaction involves the same amount of energy, but the energy flow is reversed (“in” instead of “out”): CO2(g) C(s) + O2(g) ∆H = +393.5 kJ

  49. Enthalpy calculations Chemical equation for the combustion of carbon: C(s) + O2(g) CO2(g) ∆H = –393.5 kJ 1 mole 1 mole 1 mole The combustion of twice as much carbon releases twice as much energy: 2C(s) + 2O2(g) 2CO2(g) ∆H = –787.0 kJ 2 moles 2 moles 2 moles

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