electrochemistry_sk026

electrochemistry_sk026 - Electrochemistry: Chemical Change...

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Unformatted text preview: Electrochemistry: Chemical Change and Electrical Work 9.1 Reactions in voltaic/galvanic cells 9.2 Cell potential and Standard reduction potential 9.3 Standard hydrogen electrode (SHE) 9.4 Effects of concentration on cell potential 9.5 Electrolysis ELECTROCHEMISTRY Electro chemistry A study of chemical properties & reaction of ion in a solution where: 1. chemical energy is converted to electrical energy 2. electrical energy is converted to chemical energy i. Galvanic /Voltaic Cell (chemical energy is converted to electrical energy) ii. Electrolysis Cell (electrical energy is converted to chemical energy ) Types of electrochemical cell: Chemical reactions involved in electrochemistry are : Ox idation Red uction REDOX REACTION One type of reaction cannot occur without the other. Key Points About Redox Reactions Oxidation (electron loss) always accompanies reduction (electron gain). The oxidising agent is reduced, and the reducing agent is oxidised. The number of electrons gained by the oxidising agent always equals the number lost by the reducing agent. Reduction: Occurs at cathode (+ve electrode) Electrode N (cathode) accepts electrons & the electrolyte is reduced to metal N, as a result the mass of cathode increases. Half cell reaction at cathode: N n+ (aq) + ne N(s) Oxidation: Occurs at anode (-ve electrode) Electrode M (anode) releases electrons & itself oxidised to M n+ ion Half cell reaction at anode: M (s) M n+ (aq) + ne So, overall cell reaction: N n+ (aq) + M (s) M n+ (aq) + N (s) REDUCTION gain of electron Oxidation no. decrease Reaction at cathode Remember RED CAT = RED uction at CAT hode Example: Cu 2+ + 2e- Cu Oxidation no. OXIDATION loss of electron Oxidation no. increase Reaction at anode Example: Mg Mg 2+ + 2e- Oxidation no. REDOX Reaction Reduction : Oxidation : C u 2+ (a q ) + 2e- C u (s ) Zn (s ) Zn 2 + (a q ) + 2e- Half-cell reaction C u 2+ (a q ) + Zn (s ) C u (s ) + Zn 2+ (a q ) Example Overall cell reaction : Electrochemical reaction consists of reduction and oxidation. These two reactions are called half-cell reactions The combination of 2 half reactions are called cell reaction Component and Operation of Galvanic cell Consists of : Consists of : 1) Zn 1) Zn metal in an aqueous solution of Zn 2+ 2) Cu 2) Cu metal in an aqueous solution of Cu 2+- The 2 m e ta ls a re c o nne c te d b y a wire- The 2 containers are connected by a salt bridge.- A voltmeter is used to detect voltage generated. Zn electrode Cu electrode Salt bridge Zn 2+ Cu 2+ Voltmeter Galvanic cell ZnSO 4 (aq) solution CuSO 4 (aq) solution What happens at the zinc electrode ?...
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electrochemistry_sk026 - Electrochemistry: Chemical Change...

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