Chapter 21 Lecture 3

Chapter 21 Lecture 3 - Diagramming Voltaic Cells PROBLEM...

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Unformatted text preview: Diagramming Voltaic Cells PROBLEM: Diagram, show balanced equations, and write the notation for a voltaic cell that consists of one half-cell with a Cr bar in a Cr(NO 3 ) 3 solution, another half-cell with an Ag bar in an AgNO 3 solution, and a KNO salt bridge. Measurement indicates that the Cr electrode is 3 negative relative to the Ag electrode. PLAN: Identify the oxidation and reduction reactions and write each half- action Associate the (- Cr) pole with the anode (oxidation) and the SOLUTION: reaction. Associate the ( )(Cr) pole with the anode (oxidation) and the (+) pole with the cathode (reduction). Voltmeter xidation half action salt bridge e- Oxidation half-reaction Cr( s ) Cr 3+ ( aq ) + 3e- Reduction half-reaction Cr Ag K + NO 3- Ag + ( aq ) + e- Ag( s ) Overall (cell) reaction r( + Ag + q C r 3+ q + Ag( Cr 3+ Ag + 21-23 Cr( s ) + 3Ag ( aq ) Cr ( aq ) + 3Ag( s ) Cr( s ) | Cr 3+ ( aq ) || Ag + ( aq ) | Ag( s ) 21-24 21-25 Why Does a Voltaic Cell Work? The spontaneous reaction occurs as a result of the different abilities of materials (such as metals) to give up their electrons and the ability of the electrons to flow through the circuit. electrical potential 21-26 water flow electron flow Cell Potentials lectromotive force ( mf Electromotive force ( emf ) – drives the electrons in the el. circuit – emf is the difference between the electrical potentials of the two lectrodes (voltage) electrodes (voltage) Cell potential ( E cell ) → E cell = emf – Units → volts (V) → (1 Volt (V) = 1 Joule (J)/ Coulomb (C) (Electrical work (J)= the applied voltage (V) × the charge moving between the electrodes (C)) Positive Cell potential: E cell > 0 for a spontaneous reaction Standard cell potential ( E o cell ) – the cell potential at standard-state conditions (gases → 1 atm, 21-27 solutions → 1 M, liquids & solids → pure) Measurement of a standard cell potential....
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Chapter 21 Lecture 3 - Diagramming Voltaic Cells PROBLEM...

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