1. Electrochemistry

2. Electrochemistry is the study of the relationship between the flow of electric current and chemical changes, including the conversion of chemical energy to electrical energy and vise versa! The chemical reactions take place in devices known as electrochemical cells. The two main types of electrochemical cells are the electrolytic cell and the voltaic cell. ELECTRICITYVSCHEMICAL REACTIONS

3. Electrochemistry An electrolytic cell is a device in which electricity is used to produce a chemical reaction (electrons are forced to flow) that is otherwise nonspontaneous! A voltaic cell is a device in which a spontaneous chemical reaction (electrons flow on their own) is used to produce electricity! BATTERIES ARE AN EXAMPLE OF VOLTAIC CELLS! In both an electrolytic cell and a voltaic cell, the redox reaction is separated into two half reactions. Each half reaction takes place at an electrode.

4. Electrochemistry The electrode where reduction ALWAYS takes place is called the cathode (red cat). Electrons ALWAYS flow to the cathode. Cations ALWAYS flow to the cathode. The electrode where oxidation ALWAYS takes place is called the anode (an ox). Anions ALWAYS flow to the anode. Electrons ALWAYS will flow spontaneously from the negative electrode to the positive electrode through the external connecting wire (opposite charges attract)!

5. Electrochemistry V switch Zn Ag Zn 2+ Ag 1+ X 1- cathodeanode Reduction occurs here.Oxidation occurs here. e - e - e -

6. Electrochemistry battery + - Reduction occurs here.Oxidation occurs here. anode cathode e - e - e -

7. Electrochemistry In an electrolytic cell, the cathode is the negative electrode and the anode is the positive electrode battery + - cathodeanode - +

8. Electrochemistry in a voltaic cell, the cathode is the positive electrode and the anode is the negative electrode. V switch Zn Ag Zn 2+ Ag 1+ X 1- anodecathode - +

9. Electrochemistry Ex. (1) Reduction occurs at the cathode in (1) electrolytic cells, only (2) voltaic cells, only (3) both electrolytic cells and voltaic cells (4) neither electrolytic cells nor voltaic cells Ex. (2) Which energy transformation occurs when a voltaic cell is in operation? (1) chemical energy → electrical energy (2) electrical energy → chemical energy (3) light energy → heat energy (4) light energy → chemical energy

10. Electrochemistry Ex. (3) Which energy transformation occurs when an electrolytic cell is in operation? (1) chemical energy → electrical energy (2) electrical energy → chemical energy (3) light energy → heat energy (4) light energy → chemical energy Ex. (4) Which statement is true for any electrochemical cell? (1) Oxidation occurs at the anode, only. (2) Reduction occurs at the anode, only. (3) Oxidation occurs at the anode and the cathode. (4) Reduction occurs at the anode and the cathode.

11. Electrochemistry Ex. (5) In a voltaic cell, cations flow to the (1) cathode but in an electrolytic cell cations flow to the anode. (2) anode but in an electrolytic cell cations flow to the cathode. (3) cathode and in an electrolytic cell cations also flow to the cathode. (4) anode and in an electrolytic cell cations also flow to the anode.

12. Electrochemistry Ex. (6) In a voltaic cell, electrons flow to the positively charged (1) anode but in an electrolytic cell electrons flow to the negatively charged anode. (2) cathode but in an electrolytic cell electrons flow to the negatively charged anode. (3) anode but in an electrolytic cell electrons flow to the negatively charged cathode. (4) cathode but in an electrolytic cell electrons flow to the negatively charged cathode.