Electricity driving nonspontaneous chemical reactions

Electrolysis Driving Nonspontaneous Chemical Reactions with Electricity 890... 

In a galvanic cell, a spontaneous chemical reaction generates an electrical current. It is also possible to use an electrical current to drive a nonspontaneous chemical reaction. The recharging of a dead battery uses an external electrical current to drive the batteiy reaction in the reverse, or uphill, direction. 

Electric current from an external source is used to drive a nonspontaneous chemical reaction in an electrolytic cell. The amount of product formed or reactant consumed depends on the quantity of electricity transferred at the electrode. 

In an electrolytic cell, electric current drives the chemical reaction. The chemical reaction involved in an electrolytic cell is nonspontaneous. Electric current is used to drive the reaction. This process is called electrolysis and hence the name, electrolytic cell. The reaction involves the transfer of electrons and thus it is a redox reaction. For further understanding of the functioning of an electrolytic cell, we will look at an example of an electrolytic cell involving the electrolysis of molten sodium chloride. Molten sodium chloride is a good conductor of electricity. The melting point of NaCl is around 800° C. 

Electrochemical processes are redox reactions in which the energy released by a spontaneous reaction is converted to electricity or in which electricity is used to drive a nonspontaneous chemical reaction. The latter type is called electrolysis. 

The generation of electricity through redox reactions is normally carried out in a device called an electrochemical cell. A voltaic (or galvanic) cell, is an electrochonical cell that produces electrical current from a spontaneous chemical reaction. A second type of electrochemical cell, called an electrolytic cell, consumes electrical current to drive a nonspontaneous chemical reaction. We discuss voltaic cells in this section and electrolytic cells in Section 18.8. 

Electrochemistry is the branch of chemistry that deals with the use of spontaneous chemical reactions to produce electricity and the use of electricity to drive nonspontaneous reactions forward. Electrochemical techniques—procedures based on electrochemistry—allow us to use electronic equipment to monitor concentrations of ions in solution. We can use them to monitor the composition and pH of solutions and to determine the pKa of acids. Electrochemistry even allows us to monitor the activity of our brain and heart (perhaps while we are trying to master chemistry), the pH of our blood, and the presence of pollutants in our water supply. 

So far, we ve focused our attention on voltaic cells, which rely on spontaneous chemical reactions to drive them. In this section, we will look more closely at a different type of cell—one that requires electrical energy from an external source to allow a nonspontaneous reaction to occur. This new type of reaction is known as electrolysis, and it takes place in an electrolytic cell. 

The next several sections describe battery cells, or voltaic cells (also called galvanic cells). These are a kind of electrochemical cell. An electrochemical cell is a system consisting of electrodes that dip into an electrolyte and in which a chemical reaction either uses or generates an electric current. A voltaic, or galvanic, cell is an electrochemical cell in which a spontaneous reaction generates an electric current. An electrolytic cell is an electrochemical cell in which an electric current drives an otherwise nonspontaneous reaction. In the next sections, we will discuss the basic principles behind voltaic cells and then explore some of their commercial uses. 

Electrochemistry is the area of chemistry concerned with the interconversion of chemical and electrical energy. Chemical energy is converted to electrical energy in a galvanic cell, a device in which a spontaneous redox reaction is used to produce an electric current. Electrical energy is converted to chemical energy in an electrolytic cell, a cell in which an electric current drives a nonspontaneous reaction. It s convenient to separate cell reactions into half-reactions because oxidation and reduction occur at separate electrodes. The electrode at which oxidation occurs is called the anode, and the electrode at which reduction occurs is called the cathode. 

Recall that the voltaic cells convert chemical energy to electrical energy as a result of a spontaneous redox reaction. Electrolytic cells do just the opposite they use electrical energy to drive a nonspontaneous reaction. A common example is the electrolysis of water. In this case, an electric current decomposes water into hydrogen and oxygen. 

An electrolytic cell, you may recall, is an electrochemical cell in which an electric current drives an otherwise nonspontaneous reaction. The process of producing a chemical change in an electrolytic cell is called electrolysis. Many important substances, including aluminum and chlorine, are produced commercially by electrolysis. We will begin by looking at the electrolysis of molten salts. 

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