ch21 - CHAPTER 21 ELECTROCHEMISTRY: CHEMICAL CHANGE AND...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
CHAPTER 21 ELECTROCHEMISTRY: CHEMICAL CHANGE AND ELECTRICAL WORK 21.1 Oxidation is the loss of electrons (resulting in a higher oxidation number), while reduction is the gain of electrons (resulting in a lower oxidation number). In an oxidation-reduction reaction, electrons transfer from the oxidized substance to the reduced substance. The oxidation number of the reactant being oxidized increases while the oxidation number of the reactant being reduced decreases. 21.2 No , one half-reaction cannot take place independently of the other because there is always a transfer of electrons from one substance to another. If one substance loses electrons (oxidation half-reaction), another substance must gain those electrons (reduction half-reaction). 21.3 Spontaneous reactions, Δ G sys < 0, take place in voltaic cells, which are also called galvanic cells. Nonspontaneous reactions take place in electrolytic cells and result in an increase in the free energy of the cell ( Δ G sys > 0). 21.4 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. 21.5 a) To decide which reactant is oxidized, look at oxidation numbers. Cl is oxidized because its oxidation number increases from –1 in Cl to 0 in Cl 2 . b) MnO 4 is reduced because the oxidation number of Mn decreases from +7 in MnO 4 to +2 in Mn 2+ . c) The oxidizing agent is the substance that causes the oxidation by accepting electrons. The oxidizing agent is the substance reduced in the reaction, so MnO 4 is the oxidizing agent. d) Cl is the reducing agent because it loses the electrons that are gained in the reduction. e) From Cl , which is losing electrons, to MnO 4 , which is gaining electrons. f) 8 H 2 SO 4 ( aq ) + 2 KMnO 4 ( aq ) + 10 KCl( aq ) 2 MnSO 4 ( aq ) + 5 Cl 2 ( g ) + 8 H 2 O( l ) + 6 K 2 SO 4 ( aq ) 21.6 2 CrO 2 ( aq ) + 2 H 2 O( l ) + 6 ClO ( aq ) 2 CrO 4 2 ( aq ) + 3 Cl 2 ( g ) + 4 OH ( aq ) a) The CrO 2 is the oxidized species because Cr increases in oxidation state from +3 to +6. b) The ClO is the reduced species because Cl decreases in oxidation state from +1 to 0. c) The oxidizing agent is ClO ; the oxidizing agent is the substance reduced. d) The reducing agent is CrO 2 ; the reducing agent is the substance oxidized. e) Electrons transfer from CrO 2 to ClO . f) 2 NaCrO 2 ( aq ) + 6 NaClO( aq ) + 2 H 2 O( l ) 2 Na 2 CrO 4 ( aq ) + 3 Cl 2 ( g ) + 4 NaOH( aq ) 21.7 a) Divide into half-reactions: C l O 3 ( aq ) Cl ( aq ) I ( aq ) I 2 ( s ) Balance elements other than O and H C l O 3 ( aq ) Cl ( aq ) chlorine is balanced 2 I ( aq ) I 2 ( s ) iodine now balanced Balance O by adding H 2 O C l O 3 ( aq ) Cl ( aq ) + 3 H 2 O( l ) add 3 waters to add 3 O’s to product 2 I ( aq ) I 2 ( s ) n o c h a n g e 21-1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Balance H by adding H + C l O 3 ( aq ) + 6 H + ( aq ) Cl ( aq ) + 3 H 2 O( l ) add 6 H + to reactants 2 I ( aq ) I 2 ( s ) n o c h a n g e Balance charge by adding e C l O 3 ( aq ) + 6 H + ( aq ) + 6 e Cl ( aq ) + 3 H 2 O( l ) add 6 e
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 10/06/2010 for the course CHM 2046 taught by Professor Veige/martin during the Spring '07 term at University of Florida.

Page1 / 29

ch21 - CHAPTER 21 ELECTROCHEMISTRY: CHEMICAL CHANGE AND...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online