This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: 21 Chapter Electrochemistry: Chemical Change and Electrical Work 21.1 Oxidation is a loss of electron( s ) and an increase in oxidation number. Reduction is a gain of electron( s ) and a decrease in oxidation number. 21.2 An electrochemical process involves an electron flow. At least one substance must lose electron( s ) and one substance must gain electron( s ) to produce the flow. This electron transfer is a redox process. 21.3 No. Oxidation is always accompanied by reduction. Electrons cannot be created or destroyed, only transferred. 21.4 O 2- is too strong a base to exist in H 2 O. The reaction O 2- + H 2 O B 2OH- occurs. Only species actually existing in solution can be used to balance an equation. 21.5 Multiply each half-reaction by the appropriate integer to make e- lost equal to e- gained. 21.6 Add an equal number of OH- ions to both sides to neutralize H + ions and produce H 2 O. 21.7 No. Add spectator ions to the balanced ionic equation to obtain the balanced molecular equation. 21.8 A voltaic or galvanic cell has a ∆ G sys < 0. An electrolytic cell has a ∆ G sys 0, meaning an increase in free energy. 21.9 a) True. b) True. c) True. d) False. In a voltaic cell, the system does work on the surroundings. e) True. f) False. The electrolyte in a cell provides a solution of mobile ions to maintain charge neutrality. 21.10 16H + ( aq ) + 2MnO 4- ( aq ) + 10Cl- ( aq ) B 2Mn 2 + ( aq ) + 5Cl 2 ( g ) + 8H 2 O( l ) a) Cl- b) MnO 4- c) MnO 4- d) Cl- e) From Cl- to MnO 4- f) 8H 2 SO 4 ( aq ) + 2KMnO 4 ( aq ) + 10KCl( aq ) B 2MnSO 4 ( aq ) + 6K 2 SO 4 ( aq ) + 5Cl 2 ( g ) + 8H 2 O( l ) 21.11 2 CrO 2- ( aq ) + 2 H 2 O( l ) + 6 ClO- ( aq ) B 2 CrO 4 2- ( aq ) + 3 Cl 2 ( g ) + 4 OH- ( aq ) a) CrO 2- b) ClO- c) ClO- d) CrO 2- e) from CrO 2- to ClO- f) 2 NaCrO 2 ( aq ) + 6 NaClO( aq ) + 2 H 2 O( l ) B 2 Na 2 CrO 4 ( aq ) + 3 Cl 2 ( g ) + 4 NaOH( aq ) 21.12 a) ClO 3- ( aq ) + 6I- ( aq ) + 6H + ( aq ) B Cl- ( aq ) + 3I 2 ( s ) + 3H 2 O( l ) oxidizing agent: ClO 3- ; reducing agent: I- b) 2MnO 4- ( aq ) + 3SO 3 2- ( aq ) + H 2 O( l ) B 2MnO 2 ( s ) + 3SO 4 2- ( aq ) + 2OH- ( aq ) oxidizing agent: MnO 4- ; reducing agent: SO 3 2- c) 2MnO 4- ( aq ) + 5H 2 O 2 ( aq ) + 6H + ( aq ) B 2Mn 2 + ( aq ) + 5O 2 ( g ) + 8H 2 O( l ) oxidizing agent: MnO 4- ; reducing agent: H 2 O 2 21.13 a) 3O 2 ( g ) + 4NO( g ) + 2H 2 O( l ) B 4NO 3- ( aq ) + 4H + ( aq ) oxidizing agent: O 2 ; reducing agent: NO b) 2CrO 4 2- ( aq ) + 8H 2 O( l ) + 3Cu( s ) B 2Cr(OH) 3 ( s ) + 3Cu(OH) 2 ( s ) + 4OH- ( aq ) oxidizing agent: CrO 4 2- : reducing agent: Cu c) AsO 4 3- ( aq ) + NO 2- ( aq ) + H 2 O( l ) B AsO 2- ( aq ) + NO 3- ( aq ) + 2OH- ( aq ) oxidizing agent: AsO 4 3- ; reducing agent: NO 2- ....
View Full Document