Chapter 7: Chemical Reactions

Transcription

1 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 1 Chapter 7: Chemical Reactions Read Chapter 7 and Check MasteringChemistry due dates. Evidence of Chemical Reactions: Changes occur in the chemical composition Color change Formation of solid Formation of gas Emission of light Change in temperature without externally adding or removing heat. Try this #1: Are you fooled into thinking all changes are evidence of chemical reactions Is boiling water (liquid to gas) a chemical change? Is separation of CuSO4 from sand by dissolving the CuSO4 in water and filtering the sand a chemical change?

2 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 2 The Chemical Equation: Reactants Products Phases: solid (s), liquid (l), gas (g), aqueous (aq) Balancing Chemical Equations: Balance the same number of atoms on either side Total charges must also balance on each side Once the formulas are correctly written, add numbers to coefficients (never change a subscript to balance) Process: Write skeletal equation with correct chemical formulas as reactants and products Start with a substance with the most atoms and subscripts If an element occurs in only one compound on both sides, that element should be balanced first. If more than one choice is available, balance metals before nonmetals Balance a free element last, adjust the coefficient on the fee element Remove fractions by multiplying through by the denominator Check The number of a particular type of atom within a chemical formula embedded in an equation is obtained by multiplying the subscript for the atom by the coefficient for the chemical formula. If there is no coefficient or subscript, a 1 is implied. An example of the balanced equation for the combustion of natural gas follows:

3 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 3 Try this #2: Practice balancing the following: a) carbon dioxide gas and water forms carbonic acid b) C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O (l) c) Pb(NO 3 ) 2 (aq) + K 2 S (aq) PbS (s) + KNO 3 (aq) d) solid zinc is added to hydrochloric acid to produce hydrogen gas and aqueous zinc chloride e) NH 3 (g) + O 2 (g) NO 2 (g) + H 2 O (l) f) aqueous acetic acid and potassium sulfite react to form aqueous potassium acetate, water and sulfur dioxide gas.

4 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 4 Electrolytes in Aqueous Solution: Pure water does not conduct electricity. If charged ions are dissolved in water it will conduct electricity. Strong Electrolytes will dissociate into its ions in an aqueous solution and are written as separated ions in the total and net ionic reactions. Examples: Strong acids, Strong Bases, Soluble salts. Strong Acids: HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4, HClO 3 Strong Bases: soluble hydroxides from Group IA (not including H) and Group IIA, not including the top two: LiOH, NaOH, KOH, RbOH, Ca(OH) 2, Sr(OH) 2, Ba(OH) 2 Soluble Salts: Ionic compounds that contain cations from Group 1A; Li +, Na +, K +, or NH 4 + or the anions NO 3-1, ClO 4-1, C 2 H 3 O 2-1 are mostly soluble. Compounds with Cl -1, Br -1, I -1 are soluble except with Ag +, Hg 2 +2, Pb +2 Compounds with SO 4-2 are soluble except Sr +2, Ba +2, Pb +2 or Ca +2. Weak Electrolytes will partially dissociate into its ions in an aqueous solution, but are written together in an ionic equation. Weak electrolytes are the weak acids and weak bases such as HC 2 H 3 O 2 or NH 3

5 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 5 Nonelectrolytes will stay together in an aqueous solution. Nonelectrolytes are the insoluble salts [solids], and molecular gases and liquids. Solubility Rules: familiarize yourself with the top portion of ions mostly soluble

6 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 6 Writing Molecular, Ionic, and Net ionic equations: Example: For the double displacement reaction of lead (II) nitrate reacting with potassium iodide. Whole equation: Balanced Pb(NO 3 ) 2 (aq) + 2 KI (aq) PbI 2 (s) + 2 KNO 3 (aq) Total ionic equation: Pb +2-1 (aq) + 2 NO 3 (aq) + 2 K +1 (aq) + 2 I -1 (aq) PbI 2 (s) + 2 K +1-1 (aq) + 2 NO 3 (aq) Identify the spectator ions and leave them out when writing the net ionic eq. Net ionic equation: Pb +2 (aq) + 2 I -1 (aq) PbI 2 (s) This is a double displacement reaction and specifically a precipitation reaction. (D-D) double displacement type reactions: AB + CD AD + CB A chemical composition change has occurred. The visible evidence of this change is the formation of yellow solid. Two colorless liquids react to form the new yellow solid PbI 2. Try this #3: Follow the rules above to write the Molecular, Ionic, and Net ionic equations for the reaction of aqueous calcium chloride and aqueous potassium carbonate. Whole equation: Total ionic equation: Identify the spectator ions and leave them out when writing the net ionic eq. Net ionic equation

7 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 7 Classifying Chemical Reaction Types: (D-D) double displacement (N) neutralization or acid-base, (P) precipitation (R) redox or oxidation-reduction (SR) single replacement (C) combustion (G) gas evolution (Syn) synthesis or combination (D) decomposition Classifying and Predicting Products and Chemical Reactions: The following examples will help you classify the type of reaction and predict the expected products. (D-D) double displacement: AB + CD AD + CB A double displacement reaction starts with two ionic compounds in which the ions exchange to produce new balanced ionic compounds. Always write the cation before the anion and verify that the net charge of each compound is zero. Ionic compounds may be acid, base, or salt. Oxidation charges do not alter in double displacement reactions so this type will never be a redox reaction. Driving forces for double displacement reactions include formation of a solid (P) Precipitation, Check solubility rules formation of water (N) Neutralization or Acid-Base Reaction formation of a weak electrolyte (WE) Reactions do not always occur when mixing two aqueous solutions. (NR) no reaction (P) Formation of a new solid in a double displacement reaction when there is no solid on the reactant side is called PRECIPITATION. Ni(NO 3 ) 2 (aq) + Na 2 S (aq) NiS (s) + 2 NaNO 3 (aq) DD,P

8 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 8 (N) Formation of water in a double displacement reaction is called NEUTRALIZATION (also known as Acid-Base reaction) 3 KOH (aq) + H 3 PO 4 (aq) K 3 PO 4 (aq) + 3 H 2 O (l) DD,N (WE) Formation of a WEAK ELECTROLYTE, generally a weak acid, produced from a double displacement reaction Al(C 2 H 3 O 2 ) 3 (aq) + 3 HCl (aq) AlCl 3 (aq) + 3 HC 2 H 3 O 2 (aq) DD,WE (NR) When all ionic products are strong electrolytes, there is NO REACTION. FeBr 3 (aq) + 3 LiNO 3 (aq) 3LiBr (aq) + Fe(NO 3 ) 3 (aq) NR (G) Gas Evolution: Several common compounds are in the gas phase. You should recognize the following as gases. CO 2, SO 2, CH 4, NH 3, H 2 S, H 2, N 2, O 2, F 2, Cl 2, NO, NO 2 Special cases of (G) Gas Evolution in (DD) Double Displacement: There are three common products that further decompose leading to three products in place of just the two products in a double displacement reaction. They are as follows. NH 4 OH (aq) H 2 SO 3 (aq) H 2 CO 3 (aq) NH 3 (g) + H 2 O (l) SO 2 (g) + H 2 O (l) CO 2 (g) + H 2 O (l)

9 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 9 The double displacement reactions below show examples of the decomposition of one of the ionic products. The driving forces include both formation of water and a gas, because water is formed these can be labeled Neutralization reactions. The last one is DD, N, and P. K 2 CO 3 (aq) + 2HCl (aq) H 2 CO 3 (aq) + 2 KCl (aq) K 2 CO 3 (aq) + 2HCl (aq) CO 2 (g) + H 2 O (l) + 2 KCl (aq) Na 2 SO 3 (aq) + 2HCl (aq) H 2 SO 3 (aq) + 2 NaCl (aq) Na 2 SO 3 (aq) + 2HCl (aq) SO 2 (g) + H 2 O (l) + 2 NaCl (aq) (NH 4 ) 2 SO 4 (aq) + Ba(OH) 2 (aq) 2 NH 4 OH (aq) + BaSO 4 (s) (NH 4 ) 2 SO 4 (aq) + Ba(OH) 2 (aq) 2 NH 3 (g) + 2 H 2 O (l) + BaSO 4 (s) Try this #4: Write an equation for the precipitation reaction that occurs (if any) when solutions of sodium carbonate Na2CO3(aq) and copper(ii) chloride CuCl2(aq) are mixed. Predict the products and balance for the reaction that geologist use to test for carbonates in rock or mineral samples HNO3 (aq) + CaCO3 (s) (marble)

10 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 10 (Syn) Synthesis or combination: A + B AB A synthesis reaction starts with two or more substances and creates a single compound product. The reverse of a synthesis reaction is Decomposition. Remember which elements are diatomic elements: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2. Know the elements in their pure form: gas (red), solid (black), and liquid (blue), by color on the periodic table in the classroom. a) two elements (metal plus nonmetal) ionic compound. Na (s) + Cl 2 (g) NaCl (s) Balance this b) metal oxide and water base (metal hydroxide) BaO (g) + H 2 O (l) Ba(OH) 2 (aq) c) nonmetal oxide and water acid CO 2 (g) + H 2 O (l) H 2 CO 3 (aq) Try this #5: Balance the synthesis reactions Al (s) + O2 (g) Al2O3 (s) Na2O (s) + H2O (l) NaOH (aq)

11 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 11 (D) Decomposition: AB A + B A decomposition reaction starts with one reactant and breaks up into two or more substances. The reverse of a decomposition reaction is synthesis. Remember the diatomic elements: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2. a) Water can be broken into its elements by electrolysis b) ionic compound two elements (metal plus nonmetal) 2 Fe 2 O 3 (s) 4 Fe (s) + 3 O 2 (g) c) metal carbonate metal oxide and carbon dioxide CaCO 3 (s) CaO (s) + CO 2 (g) d) metal bicarbonate metal carbonate + water + carbon dioxide 2 Al(HCO 3 ) 3 (s) Al 2 (CO 3 ) 3 (s) + 3 H 2 O (l) + 3 CO 2 (g) e) metal connected to halogen with oxygen metal halide + oxygen Ca(BrO 3 ) 2 (s) CaBr 2 (s) + 3 O 2 (g) f) hydrated salt anhydrous salt plus water CuSO. 4 5H 2 O (s) CuSO 4 (s) + 5 H 2 O (l)

12 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 12 Try this #6: Balance the decomposition reactions that occur after heating CoCl2. 6H2O (s) CoCl2 (s) + 6H2O (l) KClO3 (s) KCl (s) + O2 (g) NaHCO3 (s) Na2CO3 (s) + H2O (l) + CO2 (g) (R) Redox or oxidation-reduction reactions: Redox reactions transfer electrons. A way to tell that a redox reaction takes place is to check for element charges and see if they change from reactant side to product side. If on one side of the reaction an atom or molecule has a zero charged element and on the other side of the reaction the same atom is now part of a compound or an ion, then electrons have been moved. Some synthesis and decomposition reactions are redox. All combustion and single replacement reactions are redox reactions. Oxidation Reduction increases oxidation number reduces oxidation number lose electrons gain electrons 2 Cl -1 Cl e - K e - K OIL RIG Oxidation is losing electrons reduction is gaining electrons Leo the lion Lose electrons is oxidation growls Ger gain electrons is reduction (C) Combustion: elements burn with O 2 gas to produce oxides, Common products include: CO 2, H 2 O, NO 2, SO 2. CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l)

13 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 13 Try this #7: Predict the products and balance C 4 H 10 (l) + O 2 (g) C 6 H 14 S (s) + O 2 (g) C 12 H 22 O 11 (s) + O 2 (g) NH 3 (g) + O 2 (g) Another Redox [Oxidation-Reduction] type reaction: Chem 12: identify classification or balance, but not necessary to predict the products for this class. Try this #8: (SR) Single Replacement: A + BC AC + B The more active element will have a partner, less active is alone. Activity series: Au<Hg<Ag<Cu<H 2 <Pb<Sn<Ni<Fe<Cr< Zn<Mn<Al< Mg< Na<Ca< K<Li Predict the products if a reaction occurs or write NR for no reaction Zn(NO 3 ) 2 (aq) + Cu (s) Cu(NO 3 ) 2 (aq) + Zn (s) Redox Applications: Combustion, Bleaching, Batteries, Fuel cells, Metallurgy, Corrosion, Respiration

14 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 14 Practice Problems: 1. List the elements that are diatomic. 2. Name several driving forces for a chemical reaction. 3. Name several signs of evidence that would indicate a chemical reaction happened. 4. What information can one obtain from a balanced chemical equation? 5. For the following double-displacement reaction: a) Complete the whole equation by including the products and balance the equation. Include the physical states in all the equations. NaCl (aq) + AgNO 3 (aq) b) Write the balanced total ionic equation for the above reaction. Include charges on ions. Circle the spectator ions in part b? c) Write the balanced net ionic equation for this reaction. d) What is/are the driving force(s) for this reaction? 6. Crude gunpowders often contain a mixture of solid potassium nitrate and charcoal (solid carbon). When such a mixture is heated until a reaction occurs, a solid residue of potassium carbonate is produced. The explosive force of the gunpowder comes from the fact that two gases are also produced, carbon monoxide and nitrogen, which increase in volume with great force and speed. Write the balanced chemical equation for the reaction.

15 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e Balance and Classify in as many ways possible the following reactions. Possible classifications: (D-D) double displacement (N) neutralization or acid-base, (P) precipitation (R) redox or oxidation-reduction (SR) single replacement (C) combustion (G) gas evolution (Syn) synthesis or combination (D) decomposition (NR) no reaction a) Mg(ClO 3 ) 2 (s) MgCl 2 (s) + O 2 (g) b) N 2 (g) + O 2 (g) N 2 O 5 (g) c) C 6 H 6 (l) + O 2 (g) CO 2 (g) + H 2 O (g) d) KOH (aq) + H 2 SO 4 (aq) K 2 SO 4 (aq) + H 2 O (l) e) AgNO 3 (aq) + Na 2 CrO 4 (aq) Ag 2 CrO 4 (s) + NaNO 3 (aq) f) aqueous silver nitrate and solid copper reacts to form aqueous copper (II) nitrate and solid silver. g) solid magnesium carbonate heated produces carbon dioxide gas and solid magnesium oxide h) C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O (g) i) Fe (s) + Br 2 (l) FeBr 3 (s) j) H 2 SO 4 (aq) + Na 2 CO 3 (aq) Na 2 SO 4 (aq) + H 2 O(l) + CO 2 (g)

16 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e 16 k) Al 2 (CO 3 ) 3 (s) Al 2 O 3 (s) + CO 2 (g) l) HC 2 H 3 O 2 (aq) + Mg (s) H 2 (g) + Mg(C 2 H 3 O 2 ) 2 (aq) m) Ni(NO 3 ) 2 (aq) + K 2 S (aq) NiS (s) + KNO 3 (aq) n) KOH (aq) + (NH 4 ) 2 SO 4 (aq) NH 3 (g) + K 2 SO 4 (aq) + H 2 O (l) o) Al (s) + O 2 (g) Al 2 O 3 (s) p) Fe(ClO 3 ) 3 (s) FeCl 3 (s) + O 2 (g) q) Ag (s) + HI (aq) AgI (s) + H 2 (g) r) H 2 O (l) + N 2 O 3 (g) HNO 2 (aq) s) aqueous sodium hydroxide and sulfuric acid react to form aqueous sodium sulfate and liquid water t) octane gas and oxygen gas react to form carbon dioxide gas and water. u) aqueous potassium sulfide and lead II nitrate react to produce solid lead II sulfide and aqueous potassium nitrate. v) Aqueous nitric acid is added to aqueous sodium bicarbonate, the reaction produces an aqueous salt, plus a gas and a liquid.

17 C h a p t e r 7, C h a p t e r 1 6 ( 2-5 ) : C h e m i c a l R e a c t i o n s P a g e Complete and Balance the following chemical reactions. Include the state that the substances are in, (s), (l), (g), or (aq). If no reaction in a double displacement then write No reaction. a) Combustion reaction: C 7 H 16 (s) + O 2 (g) b) Double Displacement reaction: aqueous sodium hydroxide is added to aqueous copper (II) chloride c) Double Displacement reaction: aqueous sulfuric acid is added to aqueous ammonium carbonate d) Double displacement reaction: KNO 3 (aq) + NH 4 Br (aq) e) Double Displacement reaction: HCl (aq) + Ba(OH) 2 (aq) f) Combustion Liquid pentane, C 5 H 12, reacts with atmospheric oxygen