Chemical reactions nonspontaneous

C14-0117. The notion of thermodynamic coupling of a nonspontaneous process with a spontaneous process is not restricted to chemical reactions. Identify the spontaneous and nonspontaneous portions of the following coupled processes (a) Water behind a dam passes through a turbine and generates electricity, (b) A gasoline engine pumps water from a valley to the top of a hill. 

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. 

Many exothermic reactions are spontaneous. A critical question facing chemists in the late eighteenth century was how to tell spontaneous reactions from nonspontaneous ones without performing an experiment. What characteristics must the reactants have to proceed without the prod of added energy In other words, what drives chemical reactions ... 

Electrochemical cells produce electrical energy from a spontaneous chemical reaction. In electrolysis, the process is reversed so that electrical energy is used to carry out a nonspontaneous chemical change. A cell arranged to do this is called an electrolytic cell. An electrolytic cell is similar to an electrochemical cell except that an electrolytic cell s circuit includes a power source, for example, a battery. The same electrochemical cell terminology applies to electrolytic cells. Reduction occurs at the cathode and oxidation at the anode. 

Electrolysis A process that involves forcing a current into a cell to cause a nonspontaneous chemical reaction to occur. 

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. 

Electrochemistry The study of chem ical reactions that produce electricity, and the use of electricity to facilitate nonspontane-ous chemical reactions. 

Gibbs free energy describes the spontaneity of chemical reactions in terms of enthalpy, entropy, and temperature. Negative values signify a spontaneous reaction, while positive values are nonspontaneous. A free energy of zero denotes equilibrium conditions. 

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. 

What information is needed to be certain that a chemical reaction is nonspontaneous ... 

Electrolytic cells are those in which electrical energy from an external source causes nonspontaneous chemical reactions to occur. 

From a study of the examples mentioned and many more cases, we come to the following conclusion Exothermicity favors the spontaneity of a reaction bnt does not guarantee it. Just as it is possible for an endothermic reaction to be spontaneous, it is possible for an exothermic reaction to be nonspontaneous. In other words, we cannot decide whether or not a chemical reaction will occur spontaneously solely on the basis of energy changes in the system. To make this kind of prediction we need another thermodynamic qnantity, which turns ont to be entropy. 

In contrast to spontaneous redox reactions, which result in the conversion of chemical energy into electrical energy, electrolysis is the process in which electrical energy is used to cause a nonspontaneous chemical reaction to occur. An electrolytic cell is an apparatus for carrying out electrolysis. The same principles underlie electrolysis and the processes that take place in electrochemical cells. Here we will discuss three examples of electrolysis based on those principles. Then we will look at the quantitative aspects of electrolysis. 

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. 

There are two kinds of electrochemical cells, voltaic (galvanic) and electrolytic. In voltaic cells, a chemical reaction spontaneously occurs to produce electrical energy. The lead storage battery and the ordinary flashlight battery are common examples of voltaic cells. In electrolytic cells, on the other hand, electrical energy is used to force a nonspontaneous chemical reaction to occur, that is, to go in the reverse direction it would in a voltaic cell. An example is the electrolysis of water. In both types of these cells, the electrode at which oxidation occurs is the anode, and that at which reduction occurs is the cathode. Voltaic cells wOl be of importance in our discussions in the next two chapters, dealing with potentiometry. Electrolytic cells are important in electrochemical methods such as voltammetry, in which electroactive substances like metal ions are reduced at an electrode to produce a measurable current by applying an appropriate potential to get the nonspontaneous reaction to occur (Cha]pter 15). The current that results from the forced electrolysis is proportional to the concentration of the electroactive substance. 

In some electrochemical cells nonspontaneous chemical reactions are forced to occur by the input of electrical energy. This process is called electrolysis. An electrolytic cell consists of a container for the reaction material with electrodes immersed in the reaction material and connected to a source of direct current. Inert electrodes are often used so that they do not react. 

Electrolysis a process that Involves forcing a current through a cell to cause a nonspontaneous chemical reaction to occur. (18.8) Electrolyte a material that dissolves In water to give a solution that conducts an electric current. (4.2)... 

To understand the basic principles of operation of an energy conversion or storage device it is important to know what an electrochemical cell is. Basically, it is a device in which a chemical reaction either generates or is caused by an electric current. A galvanic cell is an electrochemical cell in which a spontaneous chemical reaction is used to generate an electric current. An electrolytic cell, in turn, is an electrochemical cell in which a reaction is driven in its nonspontaneous direction by an externally applied electric current. There are three types of galvanic cell the primary, the secondary, and the fuel cell [5,6]. 

There are two types of electrochemical cell. A galvanic cell uses a spontaneous chemical reaction to produce an external electric current. Galvanic cells are called batteries in colloquial speech. Electrolytic cells, employed for electrolysis and electroplating, use external electrical power to force nonspontaneous chemical reactions to take place. 

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. 

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