Chapter 8. Chemical Equations. Flames and sparks result when aluminum foil is dropped Into liquid bromine.

Transcription

1 Chapter 8 Chemical Equations Flames and sparks result when aluminum foil is dropped Into liquid bromine. Introduction to General, Organic, and Biochemistry 10e John Wiley & Sons, Inc Morris Hein, Scott Pattison, and Susan Arena

2 Chapter Outline 8.1 The Chemical Equation 8.2 Writing and Balancing Chemical Equations 8.3 Information in a Chemical Equation 8.4 Types of Chemical Equations 8.5 Heat in Chemical Reactions 8.6 Global Warming: The Greenhouse Effect

3 The Chemical Equation Chemical shorthand for a chemical reaction. 4Al (s) + 3O 2(g) 2Al 2 O 3(s) 1. Reactants Products 2. Whole number coefficients indicate numbers of each substance participating in the reaction. 3. Special conditions for the reaction are often written over the arrow. (Δ means heat is supplied to the reaction.) 4. Physical states of each substance are indicated.

4 The Chemical Equation Mg (s) + 2HCl (aq) NaOH (aq) + HCl (aq) H 2(g) + MgCl 2(aq) H 2 O (l) + NaCl (aq)

5 Your Turn! In the reaction: CuSO 4 + BaBr 2 CuBr 2 + BaSO 4 a. BaBr 2 and BaSO 4 are reactants b. BaSO 4 and CuBr 2 are products c. CuSO 4 and BaSO 4 are reactants d. CuSO 4 and BaBr 2 are products

6 Writing and Balancing Chemical Equations A balloon filled with a hydrogen and oxygen gas explodes when heated. The product is water vapor. 1. Identify the reaction Hydrogen gas + oxygen gas water gas 2. Write the unbalanced equation H 2(g) + O 2(g) H 2 O (g) 3. Balance the equation 2 H 2(g) + O 2(g) 2 H 2 O (g) A balanced equation has the same number of each kind of atom on each side of the equation. R = reactants P = products R 24 H 2 O P 2 4 H 12O O

7 Writing and Balancing Chemical Equations Phosphorus burns in air to produce diphosphorus pentoxide. 1. Identify the reaction phosphorus + oxygen diphosphorus pentoxide 2. Write the unbalanced equation P 4 + O 2 P 2 O 5 3. Balance the equation P O 2 2 P 2 O 5 Hint: Start with most complex compound. R 4 P P 42 P 210 O 10 5 O

8 Your Turn! Given the unbalanced equation: HCl + NH 3 NH 4 Cl When properly balanced, the sum of the balancing coefficients is a. 7 b. 5 c. 3 d. 4 e. 6 HCl + NH 3 NH 4 Cl

9 Your Turn! Given the unbalanced equation: NH 3 H 2 + N 2 When properly balanced, the sum of the balancing coefficients is a. 3 b. 6 c. 9 d. 12 2NH 3 3H 2 + N 2

10 Writing and Balancing Chemical Equations Zinc metal reacts with silver nitrate to produce zinc nitrate and silver metal. 1. Identify the reaction zinc + silver nitrate zinc nitrate + silver 2. Write the unbalanced equation Zn + AgNO 3 Zn(NO 3) 2 + Ag 3. Balance the equation 1 1 Zn + 2 AgNO 3 Zn(NO 3) Ag R 1 Zn 2 Ag 2 NO 3 Hint: Balance polyatomic ions as a unit. P 1 Zn 12 Ag 2 NO 3

11 Your Turn! Given the unbalanced equation: Co + CuSO 4 Co 2 (SO 4 ) 3 + Cu When properly balanced, the sum of the balancing coefficients is a. 6 b. 7 c. 8 d. 9 e. 10 2Co + 3CuSO 4 Co 2 (SO 4 ) 3 + 3Cu

12 Your Turn! Given the unbalanced equation: Al(OH) 3 + H 2 SO 4 Al 2 (SO 4 ) 3 + H 2 O When properly balanced, the sum of the balancing coefficients is a. 4 b. 9 c. 12 d. 24 2Al(OH) 3 + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 6H 2 O

13 Writing and Balancing Chemical Equations Ethylene burns in air to produce carbon dioxide and water. 1. Identify the reaction ethylene + oxygen carbon dioxide + water 2. Write the unbalanced equation C 2 H + O 4 2 CO 2 + H 2 O 3. Balance the equation C 2 H + O CO H 2 O Hint: Balance hydrogen and oxygen last. R 2 C 4 H 26 O P 1 2 C 24 H O

14 Acetylene (C 2 H 2 ) burns in air to produce carbon dioxide and water. 1. Identify the reaction acetylene + oxygen carbon dioxide + water 2. Write the unbalanced equation C 2 H + O 2 2 CO 2 + H 2 O 3. Balance the equation C 2 H + 5 2( O CO 2 + H 2 O ) 2 R 24 C 24 H O P 1 24C C 24 H O Hint: Use a fraction to balance O, then multiply all coefficients by two to eliminate the fraction. 2 C 2 H O 2 4 CO H 2 O

15 Your Turn! Given the unbalanced equation: C 2 H 6 + O 2 CO 2 + H 2 O When properly balanced, the sum of the balancing coefficients is a. 23 b. 19 c. 17 d. 9 e. 13 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O

16 Your Turn! Given the unbalanced equation: C 3 H 8 + O 2 CO 2 + H 2 O When properly balanced, the sum of the balancing coefficients is a. 7 b. 9 c. 15 d. 23 e. 13 C 3 H 8 + 5O 2 3CO 2 + 4H 2 O

17 Information in a Chemical Equation

18 Information in a Chemical Equation H 2(g) + F 2(g) 2HF(g) 1 molecule 1 molecule 2 molecules 2 atoms H 2 atoms F 2 atoms H + 2 atoms F 1 mol H 2 1 mol F 2 2 mol HF How many moles of HF can be made from 2 moles of hydrogen gas and 2 moles of fluorine gas? 4 moles of hydrogen fluoride gas

19 Your Turn! How many molecules of oxygen gas are needed to burn 2 molecules of propane according to the balanced equation? C 3 H 8 + 5O 2 3CO 2 + 4H 2 O a. 5 molecules of oxygen b. 6 molecules of oxygen c. 10 molecules of oxygen d. 15 molecules of oxygen

20 Types of Chemical Equations 1. Combination Reactions A + B AB 2. Decomposition Reactions AB A + B 3. Single-Displacement A + BC B + AC or A + BC C + BA 4. Double-Displacement A B+ CD AD + CB

21 Combination Reactions 1. metal + oxygen metal oxide A + B AB 2Mg (s) + O 2(g) 2MgO (s) 4Fe (s) + 3O 2(g) 2Fe 2 O 3(s) 2. nonmetal + oxygen nonmetal oxide C (s) + O 2(g) CO 2(g) 2N 2(s) + O 2(g) 2N 2 O (g)

22 Combination Reactions 3. metal + nonmetal salt A + B AB 2Al (s) + 3Br 2(l) 2AlBr 3(s) 2K (s) + I 2(s) 2KI (s) 4. metal oxide + water metal hydroxide K 2 O (s) + H 2 O (l) 2KOH (aq) SrO (s) + H 2 O (l) Sr(OH) 2(aq)

23 Combination Reactions 5. nonmetal oxide + water oxy-acid A + B AB SO 3(g) + H 2 O (l) H 2 SO 4(aq) P 2 O 5(s) + 3H 2 O (l) 2H 3 PO 4(aq) N 2 O 5(s) + H 2 O (l) 2HNO 3(aq)

24 Decomposition Reactions 1. Metal oxides decompose into metals and oxygen gas. 2HgO (s) 2Hg (l) + O 2(g) AB A + B 2PbO 2(s) 2PbO (s) + O 2(g) 2. Metal carbonates form metal oxides and CO 2. Na 2 CO 3(s) Na 2 O + CO 2(g) 3. Metal bicarbonates form metal carbonates, CO 2 and H 2 O. NaHCO 3(s) Na 2 CO 3(s) + CO 2(g) + H 2 O (g)

25 Decomposition Reactions 4. Other examples: AB A + B 2Hg 2 O 2(aq) 2NaClO 3(s) 2H 2 O (l) + O 2(g) 2NaCl (s) + 3O 2(g)

26 Single Displacement Reactions If A is a metal: A + BC B + AC If A is a nonmetal: A + BC C + BA Zn (s) + 2HCl (aq) ZnCl 2(aq) + H 2(g) When pieces of zinc metal are placed in hydrochloric acid, hydrogen bubbles form immediately.

27 Activity Series More active elements can replace less active elements. 2Al (s) + 3CuCl 2(aq) 2AlCl 3(aq) + 3Cu (s) Hg (l) + CuSO 4(aq) no reaction

28 Your Turn! Consider the following reactions: A (s) + HCl (aq) no reaction B (s) + 2HCl (aq) BCl 2(aq) + H 2(g) What is the correct activity series? a. least active A < B < H most active b. least active A < H < B most active c. least active B < H < A most active

29 Single Displacement Reactions 1. Metal + acid H 2 + salt Fe (s) + 2HCl (aq) FeCl 2(aq) + H 2 (g) Cu(s) + HCl(aq) no reaction 2. metal + water H 2 + metal oxide or metal hydroxide 2K (s) + 2H 2 O (l) 2KOH (aq) + H 2 (g) 3Fe (s) + 4H 2 O (g) Fe 3 O 4(s) + 4H 2 (g)

30 Single Displacement Reactions 3. Metal + salt metal + salt Sn (s) + 2AgNO 3(aq) Sn(NO 3 ) 2(aq) + Ag (s) Zn (s) + AlCl 3(aq) no reaction 4. halogen + halide salt halogen + halide salt F 2(g) + 2NaCl (aq) 2NaF (aq) + Cl 2 (g) I 2(s) + 2NaCl (aq) no reaction

31 Your Turn! The reaction: Ba (s) + PtCl 2(aq) BaCl 2(aq) + Pt (s), will occur if a. Pt is more active than Ba b. Ba is more active than Pt c. Ba is more active than O d. O is more active than Pt

32 Your Turn! The likely products of the reaction between Al and NiCl 2 are a. AlNi and Cl 2 b. AlCl 2 and Ni c. AlCl and Ni d. AlCl 3 and Ni e. no reaction

33 Double Replacement Reactions A B+ CD AD + CB Cations exchange anions Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) Evidence of chemical change: 1. Evolution of heat 2. Formation of precipitate 3. Formation of gas bubbles

34 Neutralization Reactions Double replacement: A B+ CD AD + CB acid + base salt + water + heat HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O (l) Detected by increase in temperature (release of heat). H 2 SO 4(aq) + Ba(OH) 2(aq) BaSO 4(s) + 2H 2 O (l) Detected by increase in temperature and formation of a cloudy precipitate.

35 Metal Oxide + Acid Reactions Double replacement: A B+ CD AD + CB metal oxide + acid salt + water Heat is released by the production of water ZnO (s) + 2HCl (aq) ZnCl 2(aq) + H 2 O (l) Na 2 O (s) + 2HCl (aq) 2NaCl (aq) + H 2 O (l)

36 Precipitation Reactions Double replacement: A B+ CD AD + CB An insoluble product (precipitate) is formed and indicated by placing an (s) after its formula in the equation. Check the solubility table in Appendix V to see if a precipitate forms. BaCl 2(aq) + Na 2 SO 4(aq) BaSO 4(s) + 2NaCl (aq) 2NaCl (aq) + Hg 2 (NO 3 ) 2(aq) 2NaNO 3(aq) + Hg 2 Cl 2(s)

37 Gas Forming Reactions Double replacement: A B+ CD AD + CB NaCl (s) + H 2 SO 4(l) NaHSO 4(s) + HCl (g) Na 2 S (aq) + 2HCl (aq) H 2 S (g) + 2NaCl (s) H 2 SO 4(aq) + 2NaCN (aq) Na 2 SO 4(aq) + 2HCN (g) Double replacement reactions that form H 2 CO 3, H 2 SO 3 or NH 4 OH are quickly followed by the decomposition of these compounds into gases (indirect gas production).

38 Indirect Gas Forming Reactions metal carbonate + acid salt + CO 2(g) + H 2 O (l) Na 2 CO 3(aq) + 2HCl (aq) 2NaCl (aq) + CO 2(g) + H 2 O (l) metal sulfite + acid salt + SO 2(g) + H 2 O (l) Na 2 SO 3(aq) + 2HCl (aq) 2NaCl (aq) + SO 2(g) + H 2 O (l) ammonium salt + base salt + NH 3(g) + H 2 O (l) NH 4 NO 3(aq) + NaOH (aq) NaNO 3(aq) + NH 3(g) + H 2 O (l)

39 Your Turn! What are the likely products of the reaction of copper(ii) oxide with nitric acid? a. CuNO 3 + H 2 O b. Cu(NO 3 ) 2 + H 2 O c. Cu(NO 2 ) 2 + H 2 O d. CuNO 2 + H 2 O CuO (s) + 2HNO 3(aq) Cu(NO 3 ) 2(aq) + H 2 O (l)

40 Your Turn! What are the likely products of the reaction of sodium sulfide with iron(iii) chloride? a. FeS + NaCl b. FeS 3 + NaCl c. Fe 3 S + NaCl d. Fe 2 S 3 + NaCl 2FeCl 3(aq) + 3Na 2 S (aq) Fe 2 S 3(s) + 6NaCl (aq)

41 Your Turn! What are the likely products of the reaction of sodium hydrogen carbonate with hydrochloric acid? a. NaCl + H 2 CO 3 b. NaCl + H 2 O + CO 2 c. NaCl + H 2 O + CO 3 d. NaCl + H 2 + CO 3 NaHCO 3(aq) + HCl (aq) NaCl (aq) + H 2 O (l) + CO 2(g)

42 Heat in Chemical Reactions Endothermic reactions absorb heat O 2(g) + N 2(g) kj 2NO (g) Exothermic reactions release heat 2 Al (s) + Fe 2 O 3(s) 2Fe (s) + Al 2 O 3(s) kj The amount of heat absorbed or released is the heat of reaction.

43 Endothermic Reactions

44 Exothermic Reactions

45 Your Turn! Consider the reaction: H 2 + I kj 2 HI. When one mole of HI is produced A kj of energy is absorbed B. 6.3 kj of energy is absorbed C kj of energy is released D. 6.3 kj of energy is released

46 Global Warming: The Greenhouse Effect

47 Global Warming: The Greenhouse Effect Increased carbon dioxide levels have caused a 0.74 C rise in global temperatures over the last 100 years.