Unit 04b: Chemical Reactions

Transcription

1 1 Unit 04b: Chemical Reactions Author: S. Michalek Introductory Resources: Zumdahl v. 5 Chapter 4 Main Ideas: Classification of reactions Balancing reactions Prediction of products Writing net ionic equations Duration: 10 days Last Revision: September 5, 2007

2 2 Outline 4b.1 Classifying Reactions There are 5 basic chemical reactions. Synthesis or composition o A + B AB o Two or more reactants are combined to form one compound Decomposition o AB A + B o One reactions is broken into two or more products o Decomposition reactions are endothermic meaning the reaction absorbs heat. Single Replacement or Single Displacement o Element + Compound Element + Compound o A + BC AC + B o Single replacement reactions are reactions that involve an element replacing one part of a compound. The products include the displaced element and a new compound. An element can only replace another element that is less active than itself. Double Replacement, Double Displacement, or Metathesis o AB + CD AD + BC o In many reactions between two compounds in aqueous solutions, the cations and anions appear to switch partners. The two compounds form two new compounds. No changes in oxidation numbers. o All double replacement rations must have a driving force or a reason why the reaction occurs. The driving force in a double replacement reaction is the removal of at least one pair of ions from solution. o Removal of ions can occur in one of three ways: Formation of a precipitate a solid has formed that is insoluble in water. Formation of a gas gases may form directly from the reaction or a side decomposition reaction occurs causing the gas to form. Reactions that produce three of the gases (CO 2, SO 3, NH 3 ) involve the initial formation of a substance that breaks down to give the gas and water. H 2 SO water + SO 2 H 2 CO water + CO 2 NH 4 OH --- water + NH 3 Formation of water water is formed from an acid/base reaction. Combustion reactions o Chemical + O 2 chemical oxides o C x H y + O 2 CO 2 + H 2 O o S 8 + O 2 SO 3 o Combustion reactions are exothermic reactions that release heat.

3 3 Outline 4b.2 Balancing Reactions Now comes the fun part, balancing the reaction. The Law of Conservation of Mass states that in a chemical reaction there is no loss of mass. Each type of element will have the same mass before the reaction and after the reaction, or as reactant and product. But you can t change the materials that participate in the reaction, so you must write an integer coefficient in front of (to the left of) each material in the reaction to make sure every type of atom has the same number on each side of the reaction. Tips for Balancing Equations Be sure each molecular formula is written correctly and each compound is neutral (meaning no charge). Mentally count or tally how many of each type of atom is present on each side of the equation. Begin balancing elements that are only found in one substance on each side. Balance oxygen and hydrogen last. If there is an odd number of an element on one side and an even number on the other, the odd will need to be evened out so use a coefficient of 2 for that substance. When tallying, be sure to adjust the count for each and every element that an added coefficient affects. Combustion reactions that don t seem to balance will often turn out better if a coefficient of 2 is used for the hydrocarbon. Keep polyatomic ions grouped together in double replacement reaction. Nitrogen gas and hydrogen gas react under high pressure high temperature to form ammoni _ N 2 + _ H 2 _ NH 3 Begin with nitrogen. There are two nitrogen atoms on the left and only one on the right. In order to balance the nitrogen atoms, place a 2 in front of the ammoni _ N 2 + _ H 2 2 NH 3 There are two hydrogens on the left and six on the right. We balance the hydrogens by placing a 3 in front of the hydrogen gas. _ N H 2 2 NH 3 Now go back and check to make sure everything is balanced. There are two nitrogen and six hydrogens on both sides of the reaction. It is balanced. There is no coefficient shown in front of the nitrogen. There is no need to write ones as coefficients. The reaction equation is: N H 2 2 NH 3

4 4 Outline 4b.3a Predicting Reactions When prediction reactions you will need to follow steps in order to get the correct final balanced reaction. 1. Write out the reactants. Remember ionic compounds need to have there charges balanced. Remember your diatomic elements (H 2, O 2, N 2, Cl 2, Br 2, I 2, F 2 ) 2. Classify the reaction. 3. Use the prompts to figure out the products. Remember ionic compounds need to have there charges balanced. 4. Balance the reaction Synthesis Reactions o Element + Element Zn + Cl 2 ZnCl 2 o Compound + Compound Formation of an Acid Gas + Water Acid CO 2 + H 2 O H 2 CO 3 Formation of a Base Metal Oxide + Water CaO + H 2 O Ca(OH) 2 Metal Hydroxide Decomposition Reactions o Binary Compound a compound with two elements Compound Element + Element 2AlCl 3 2Al + 3Cl 2 o Metal Carbonate Metal Carbonate Metal Oxide + Carbon Dioxide Na 2 CO 3 Na 2 O + CO 2 o Metal Oxide Metal Oxide Metal + Oxygen Gas 2FeO 2Fe + O 2 o Metal Peroxide Metal Peroxide Metal Oxide + Oxygen Gas 2PbO 2 2PbO + O 2 o Metal Hydroxide Metal Hydroxide Metal Oxide + Water 2LiOH Li 2 O + H 2 O o Acid Acid Water + Gas Left Over H 2 SO 4 H 2 O + SO 3 o Metal Chlorate Metal Chlorate Metal Chloride + Oxygen Gas 2KClO 3 2KCl + 3O 2

5 5 Outline 4b.3b Predicting Reactions Single Replacement Reactions o Active metals replace less active metals from their compounds in aqueous solutions (SEE ACTIVITY SERIES HANDOUT). Magnesium turnings are added to a solution of iron (III) chloride. Reactants: Mg + FeCl 3 Mg is higher on the activity Series than Fe so it replaces the iron Equation: 3Mg + 2FeCl 3 2Fe + 3MgCl 2 o Active metals replace hydrogen in water. Sodium is added to water. Reactants: Na + H 2 O Equations: 2 Na + 2 H 2 O H 2 + NaOH o Active metals replace hydrogen in acids Lithium is added to hydrochloric acid Reactants: Li + HCl Equation: Li + HCl H 2 + LiCl o Active nonmetals replace less active nonmetals from their compounds in aqueous solutions (SEE ACTIVITY SERIES HANDOUT). Chlorine gas is bubbled into a solution of potassium iodide. Cl 2 + KI KCl + I 2 Double Replacement Reactions o AB + CD AD + BC o Metals will interchange and new products will be formed. Use solubility rules to find if a precipitate will form. o AgNO 3 + NaCl NaNO 3 + AgCl All chlorides are soluble except silver chloride. AgCl is the solid. Combustion Reactions o Chemical + O 2 chemical oxides o C 3 H 8 + 5O 2 3CO 2 + 4H 2 O o S 8 + O 2 SO 3 o 2C 8 H O 2 16CO H 2 O

6 6 Outline 4b.4 Writing Net Ionic Equations Net Ionic Equations In overall ionic equations, formulas of the reactants and products are written to show the predominant form of each substance as it exists in aqueous solution. Soluble salts, strong acids, and strong bases are written as separate ions. Insoluble salts, suspensions, solids, weak acids, weak bases, gases, water and organic compounds are always written as compounds. Strong Acids HCl, HI, HBr, HNO 3, H 2 SO 4. HClO 3 Net ionic Reactions 1. Write the equation and put the phases (s, l, g, aq) of each chemical. 2. Balance the equation 3. Rewrite the equations splitting the (aq) substances Overall ionic equation. 4. Cancel any ions that are found on both sides of the equation spectator ions. 5. Rewrite what is left in the reaction net ionic equation. 6. Reduce if needed Aqueous solutions of sulfuric acid and excess sodium hydroxide are combined. 1. H 2 SO 4 (aq) + NaOH (aq) H 2 O (l) + Na 2 SO 4 (aq) 2. H 2 SO 4 (aq) + 2NaOH (aq) 2H 2 O (l) + Na 2 SO 4 (aq) 3. 2H +1-2 (aq) + SO 4 (aq) + 2Na +1 (aq) + 2OH -1 (aq) 2H 2 O (l) + 2Na +1-2 (aq) + SO 4 (aq) 4. Na +1 and SO -2 4 are spectator ions and are canceled 5. 2H +1 (aq) + 2OH -1 (aq) 2H 2 O (l) 6. Reduce: H +1 (aq) + OH -1 (aq) H 2 O (l)

7 7 Handout 4b.1a Activity Series Metals: Lithium Cesium Rubidium Potassium Barium Strontium Calcium Sodium Magnesium Aluminum Manganese Zinc Chromium Iron Cadmium Cobalt Nickel Tin Lead Hydrogen Copper Silver Mercury Platinum Gold (highest reactivity) (lowest reactivity) Metals from Lithium to Sodium will replace Hydrogen from acids and water; from Magnesium to Lead they will replace Hydrogen from acids only. Activity Series of Halogens: F 2 Cl 2 Br 2 I 2 (highest reactivity) (lowest reactivity)

8 8 Handout 4b.1b Activity Series The Activity Series is a list of many of the metals found in nature, and will help you predict whether or not a single replacement reaction will occur. The metals at the top of the list are highly reactive, and the metals at the bottom are largely inert. For the purposes of this activity, we shall consider the following abridged activity series: Lithium Magnesium Gold (highest reactivity) (lowest reactivity) Lithium, the most active metal, will replace either magnesium or gold in any compound, due to its relatively high activity. Magnesium will replace gold, but not lithium. Gold will not replace either of the other two metals. So: However, Li + MgCl 2 Mg + LiCl (lithium replaces magnesium in MgCl 2 ) Mg + LiCl No Reaction (magnesium will not replace lithium in LiCl) Confused? Well, it might be instructive to personify our metals and nonmetals with more human characteristics. Our assumptions: 1. Atoms are people dancing at a party. 2. Metals are men, and nonmetals are women. 3. Reactivity is equal to attractiveness. 4. Atoms are shallow, and are hung up on good looks. So, now, let s take another look, with a slightly modified activity series. Metals: Nonmetal: Lithium Most reactive Magnesium Gold Least reactive Chlorine

9 9 Handout 4b.1c Activity Series Once again, consider the reaction: Li + MgCl 2 Mg + LiCl This equation implies that Lithium was at the party alone, and saw Magnesium dancing with Chlorine. Lithium asked to cut in, and Chlorine said yes. Lithium then proceeded to dance with Chlorine, and Magnesium went off and cried in the corner, alone and dejected. + + Lithium Magnesium with Chlorine Magnesium Lithium with Chlorine So, given our earlier assumptions, the activity series implies that a nonmetal will leave a metal with low activity for a metal with high activity. However, the opposite is not true. Consider the opposite reaction: Mg + LiCl No Reaction This equation implies that Magnesium was at the party alone, and saw Lithium dancing with Chlorine. Magnesium asked to cut in, and Chlorine said no. Lithium then continued to dance with Chlorine, and Magnesium went off and cried in the corner, yet again. + + Magnesium Lithium with Chlorine Magnesium Lithium with Chlorine Using this technique, we can predict whether or not any single replacement reaction will occur. An attractive (highly reactive) single atom will replace a less attractive (less reactive) atom that is already in a couple. It gets a bit absurd, but it works. And don t feel bad for Gold. He ll be just fine. In fact, here s a picture of him with Lithium s ex-wife.

10 10 Handout 4b.2 Solubility Rules: Water-Soluble Salts: 1. All salts of the chloride ion, Cl -1, bromide ion, Br -1, and iodide ion, I -1, are soluble except those of Ag +1, Hg 2 +2, Pb +2, Cu +1, and Tl +1. BiI 3 and SnI 4 are insoluble. PbCl 2 is three to five times more soluble in hot water than in cold water. 2. All salts of the acetate ion CH 3 CO 2-1, nitrate ion, NO 3-1, chlorate ion, ClO 3-1, perchlorate ion, ClO 4-1, and permanganate ion, MnO 4-1, are soluble. 3. All common salts of the Group 1A cations and ammonium ion, NH 4 +1, are soluble. 4. All common salts of the sulfate ion, SO 4-2, are soluble except those of Ba +2, Sr +2, Pb +2, and Hg All Group 1A and 2A salts of the bicarbonate ion, HCO 3-1, are soluble. 6. Most salts of the fluorosilicate ion, SiF 6-2, thiocyanate ion, SCN -1, and thiosulfate ion, S 2 O 3-2, are soluble. Exceptions are the Ba +2 and Group 1A fluorosilicates, the Ag +1, Hg 2 +2, and Pb +2 thiocyanates, and the Ag +1 and Pb +2 thiosulfates. Water-Insoluble Salts: 1. All common salts of the fluoride ion, F -1, are insoluble except those of Ag +1, NH 4 +1, and Group 1A cations. 2. In general, all common salts of the carbonate ion, CO 3-2, phosphate ion, PO 4-3, borate ion, BO 3-3, arsenate ion, AsO 4-3, arsenite ion, AsO 3-3, cyanide ion, CN -1, ferricyanide ion, [Fe(CN) 6 ] -3, ferrocyanide ion, [Fe(CN) 6 ] - 4, oxalate ion C 2 O 4-2, and the sulfite ion, SO 3-2, are insoluble, except those of NH 4 +1 and the Group 1A cations. 3. All common salts of the oxide ion, O -2, and the hydroxide ion, OH -1, are insoluble except those of the Group 1A cations, Ba +2, Sr +2, and NH Ca(OH) 2 is slightly soluble. Soluble oxides produce the corresponding hydroxides in water. 4. All common salts of the sulfide ion, S -2, are insoluble except those of NH 4 +1 and the cations that are isoelectronic with a noble gas. 5. Most common salts of the chromate ion, CrO 4-2, are insoluble except those of NH 4 +1, Ca +2, Cu +2, Mg +2, and the Group 1A cations. 6. All common salts of the silicate ion, SiO 3-2 are insoluble except those of the Group 1A cations.

11 11 Worksheet 4b.1 Classifying Reactions Name Classify and balance the following reactions. 1. S 8 + O 2 SO 2 2. Fe(OH) 3 + H 2 SO 4 Fe 2 (SO 4 ) 3 + H 2 O 3. Zn + HCl ZnCl 2 + H 2 4. KClO 3 KCl + O 2 5. AgNO 3 + H 2 S Ag 2 S + HNO 3 6. P 4 + O 2 P 2 O 5 7. C 9 H 20 + O 2 CO 2 + H 2 O 8. C 3 H 8 + O 2 CO 2 + H 2 O 9. H 2 O 2 H 2 O + O Na + H 2 O NaOH + H S 8 + O 2 SO Zn + NaOH Na 2 ZnO 2 + H MgCl 2 + NaOH Mg(OH) 2 + NaCl 14. C 6 H 14 + O 2 CO 2 + H 2 O 15. NaNO 3 NaNO 2 + O 2

12 12 Worksheet 4b.2 Double Replacement NAME Put numbers in the blanks to balance the following equations. Using the Solubility Rules, rewrite the equations as overall equations, ionic equations, and net-ionic equations. Be sure to include identification of phases, like (s), (l), (g), or (aq) in the reactions. DOUBLE REPLACEMENT (also known as METATHESIS): REACTION: Na 2 SO 4 + Ba(NO 3 ) 2 NaNO 3 + BaSO 4 CuHCO 3 + KBr CuBr + KHCO 3 MgCrO 4 + BaI 2 MgI 2 + BaCrO 4 NH 4 CN + Fe(NO 3 ) 3 NH 4 NO 3 + Fe(CN) 3

13 13 Worksheet 4b.3 Synthesis Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O 1. Solid beryllium is left in a container with liquid bromine. 2. Solid bismuth is burned in air. 3. Cesium is put in a container with chlorine gas. 4. Phosphorus trichloride is placed in a chlorine rich atmosphere. 5. Solid magnesium oxide is placed in water 6. Sulfur trioxide is bubbled through water. 7. Solid gold is added to fluorine gas. 8. Solid calcium oxide is added to water. 9. Nitrogen monoxide gas is bubbled through water. 10. Hydrogen and oxygen gases are mixed.

14 14 Worksheet 4b.4 Decomposition Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O 1. Potassium hydroxide is heated. 2. Lithium chlorate decomposes by heating. 3. Sodium carbonate is heated. 4. Sulfurous acid is boiled. 5. Molten aluminum chloride is electrolyzed. 6. A sample of magnesium carbonate is heated. 7. A sample of ammonium carbonate is heated. 8. Carbonic acid is boiled. 9. Hydrogen peroxide decomposes. 10. Ammonium hydroxide is heated.

15 15 Worksheet 4b.5a Single Replacement Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O 1. A piece of copper is dropped into a container of water. 2. Liquid bromine is added to a container of sodium iodide crystals. 3. An aluminum strip is immersed in a solution of silver nitrate. 4. Zinc pellets are added to a sulfuric acid solution.

16 16 Worksheet 4b.5b Single Replacement Predictions 5. Fluorine gas is bubbled into a solution of aluminum chloride. 6. Magnesium turnings are added to a solution of lead (II) acetate. 7. Iodine crystals are added to a solution of sodium chloride. 8. Calcium metal is added to a solution of nitrous acid. 9. A pea-size piece of lithium is added to water. 10. A solution of iron (III) chloride is poured over a piece of platinum wire.

17 17 Worksheet 4b.6a Double Replacement Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O 1. Ammonium sulfate and potassium hydroxide are mixed together. 2. Ammonium sulfide is reacted with hydrochloric acid. 3. Cobalt (II) chloride is combined with silver nitrate. 4. Solid calcium carbonate is reacted with sulfuric acid.

18 18 Worksheet 4b.6b Double Replacement Predictions 5. Potassium sulfite is reacted with hydrobromic acid. 6. Potassium sulfide is reacted with nitric acid. 7. Ammonium iodide is mixed with magnesium sulfate. 8. Solid titanium (IV) carbonate is added to hydrochloric acid. 9. Solid calcium sulfite is mixed with acetic acid. 10. Strontium hydroxide is added to ammonium sulfide.

19 19 Worksheet 4b.7 Combustion Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O 1. Ethanol is burned completely in air. 2. Propane is heated with oxygen gas. 3. Octane is burned in oxygen gas. 4. Copper (II) Sulfide is burned in air. 5. Solid Phosphorus is burned in air. 6. Barium sulfide is burned in air. 7. Iron is added to an oxygen rich environment. 8. Ethane is burned in oxygen gas. 9. Methane is burned in air. 10. Propanol is burned in air.

20 20 Worksheet 4b.8 Mixed Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. Identify each reaction type in the blank at the right. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O REACTION: C 5 H 12 + O 2 Zn + HCl Na 2 O Li + Cl 2 Na 2 SO 4 + LiCl C 4 H 10 + O 2 Al 2 O 3 Al + I 2 Zn(OH) 2 + Al 2 (CO 3 ) 3 FeCl 3

21 21 Worksheet 4b.9 Mixed Predictions NAME Use the General Cases to predict the products of each reaction. Balance each equation when done. Identify each reaction type in the blank at the right. General Case: Synthesis: Decomposition: Single Replacement: Double Replacement: Combustion: A + B AB AB A + B AX + B BX + A AX + BY BX + AY C x H y + O 2 CO 2 + H 2 O REACTION: CuCl 2 + Na 3 PO 4 C 12 H 26 + O 2 FeCl 3 K 2 SO 4 + Li Na + O 2 C 3 H 8 + O 2 KMnO 4 + Li Na 3 P + Ba(OH) 2 H 2 O HCl + Ca(OH) 2

22 22 Worksheet 4b.10 Mixed Predictions NAME Predict the products of each reaction. Balance each equation when done. Identify each reaction type in the blank at the right. REACTION: Mg + O 2 AlCl 3 Na + O 2 HCl + NaOH Pb(SO 4 ) 2 + Al(C 2 H 3 O 2 ) 3 C 4 H 10 + O 2 H 3 PO 4 + MgCO 3 HgCl 2 + NaSCN PtO 2 + H 2 CaCO 3 + NaCl Ag + HNO 3 NCl 3 MgSO 4 7H 2 O

23 23 Worksheet 4b.11 Mixed Predictions NAME Predict the products of each reaction. Balance each equation when done. Identify each reaction type in the blank at the right. REACTION: Sr + O 2 Na + H 2 O Zn + HCl ICl Fe(OH) 3 + H 2 SO 4 C 6 H 14 + O 2 Au(OH) 3 + Na 2 CO 3 SrCl 2 + NaOH OCl 2 AgNO 3 + H 2 SO 4 Zn + O 2 Mg(OH) 2 + NaF C 30 H 62 + O 2 Mg(NO 3 ) 2 + H 2 O Au 2 S 3 Ti(MnO 4 ) 4 + Fe 2 O 3 MnF 2 + O 2 CO 2