Spontaneous chemical reaction

Let us give the general definition of chemical induction, which reflects its specific features. At chemical induction, chemical reaction spontaneously proceeding in the system performs the effective work for another, non-spontaneous chemical reaction in the same system to proceed, which may not run without the first one. 

All reversible chemical reactions spontaneously progress toward an equilibrium mixture of constant concentrations of reactants and products. At equilibrium, some reactions yield more products than reactants others yield more reactants than products. For example, sulfur dioxide, SO2, formed in forest fires and nitrogen dioxide, NO2, formed in electrical storms, react in the atmosphere to yield sulfur trioxide, SO3 (which reaas with water to form sulfuric acid, one of the components of acid rain) and nitrogen monoxide, NO. At normal temperatures, this reaction has a 99.92% yield, so it goes almost to completion. 

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. 

Corrosive materials Flammable materials Toxic materials Reactive materials Oxygen deficiency Carcinogens Capacitors Transformers Batteries Exposed conductors Static electricity Steam Fire Solar Friction Chemical reactions Spontaneous combustion Cryogenic materials Ice, snow, wind, rain... 

Vesicle Formation by Chemical Reactions Spontaneous Vesicle Formation in Mixtures of Zwitterionic and Catanionic Surfactants... 

Chemical systems spontaneously react in a fashion that lowers their overall free energy. At a constant temperature and pressure, typical of many bench-top chemical reactions, the free energy of a chemical reaction is given by the Gibb s free energy function... 

Bromine is considered a moderate fire hazard. As liquid or vapor, it can enter spontaneous chemical reactions with reducing materials. It is a very powerful oxidizer. Bromine is considered a highly dangerous material. Upon being heated, it emits highly toxic fumes. It will react with water or steam to produce toxic and corrosive fumes. 

According to the second law of thermodynamics, for a reaction to proceed spontaneously it must produce an increase in entropy (AS > 0). Because most spontaneous chemical reactions in the body are exothermic (AH < 0), most spontaneous chemical reactions will have AG values less than zero as well. This means that if, in the reaction shown in Equation... 

Thus far we have discussed whether a chemical reaction will occur spontaneously or only with the addition of energy. We have said nothing about the rate of chemical reactions—how fast they occur. If we need to release the energy stored in our food to power the pumping of our heart and allow us to move, we need to release that energy rapidly. We cannot afford to wait hours nr days for the energy-releasing reactions to occur. 

A chemical reaction that will occur spontaneously because the energy level of the products (P) is less than the energy level of the substrate (S). (a) In the absence of an enzyme, acfivafion energy is high. Few molecules have sufficient energy to overcome this barrier and the reaction proceeds slowly if at all. (b) In the presence of an enzyme, acfivafion energy is lower and the reaction proceeds more quickly. 

A voltaic cell produces electrical energy through spontaneous redox chemical reactions. When zinc metal is placed in a solution of copper sulfate, an electron transfer takes place between the zinc metal and copper ions. The driving force for the reaction is the greater attraction of the copper ions for electrons ... 

An electrochemical cell is a device by means of which the enthalpy (or heat content) of a spontaneous chemical reaction is converted into electrical energy conversely, an electrolytic cell is a device in which electrical energy is used to bring about a chemical change with a consequent increase in the enthalpy of the system. Both types of cells are characterised by the fact that during their operation charge transfer takes place at one electrode in a direction that leads to the oxidation of either the electrode or of a species in solution, whilst the converse process of reduction occurs at the other electrode. 

The oxidation of hydrogen to water (Hj -t- i Oj -> HjO) is thermodynamically spontaneous and the energy released as a result of the chemical reaction appears as heat energy, but the decomposition of water into its elements is a non-spontaneous process and can be achieved only by supplying energy from an external source, e.g. a source of e.m.f. that decomposes the water electrolytically. Furthermore, although the heat produced by the spontaneous reaction could be converted into electrical energy, the electrical... 

Instead it turns out that in almost all cases die reverse is true. Nearly all exothermic chemical reactions are spontaneous at 25°C and 1 atm. Consider, for example, the formation of water from the elements and the rusting of iron ... 

Another difficulty is that spontaneous chemical reactions do not go to completion. Even if a spontaneous reaction is exothermic, it proceeds only till it reaches equilibrium. But in our golf ball analogy, equilibrium is reached when all of the golf balls are on the lower level. Oui analogy would lead us to expect that an exothermic reaction would proceed until all of the reactants are converted to products, not to a dynamic equilibrium. 

Chemical reactions proceed spontaneously to approach the equilibrium state. 

If a chemical reaction occurs spontaneously, the available energy of the system necessarily diminishes by an amount equal to the work which could be done by the system if the given change were executed reversibly. If the reaction occurs at constant temperature, this is equal to the diminution of free energy of the system, this being the energy available at constant temperature. It is usual to refer to the work available at constant... 

The determination of ArG° for a chemical reaction is very useful in predicting the course of the reaction. Qualitatively, we will show in Chapter 5 that with ArC°<0, the reaction is spontaneous, at least when products and reactants are in their standard state condition. Quantitatively, we will see in Chapter 9 that ArG° can be used to calculate the equilibrium constant for the reaction, from which the final equilibrium conditions can be determined. 

The decrease in Gibbs free energy as a signpost of spontaneous change and AG = 0 as a criterion of equilibrium are applicable to any kind of process, provided that it is occurring at constant temperature and pressure. Because chemical reactions are our principal interest in chemistry, we now concentrate on them and look for a way to calculate AG for a reaction. 

The thermodynamic function used as the criterion of spontaneity for a chemical reaction is the Gibbs free energy of reaction, AG (which is commonly referred to as the reaction free energy ). This quantity is defined as the difference in molar Gibbs free energies, Gm, of the products and the reactants ... 

Vehicle air bags protect passengers by allowing a chemical reaction to occur that generates gas rapidly. Such a reaction must be both spontaneous and explosively fast. A common reaction is the decomposition of sodium azide, NaN , to nitrogen gas and sodium metal. 

What Are the Key Ideas The tendency of electrons to be transferred in a chemical reaction depends on the species involved and their concentrations. When the process is spontaneous and reduction and oxidation occur at different locations, the reaction can do work and drive electrons through an external circuit. 

These early observations have evolved into the branch of chemistry called electrochemistry. This subject deals not only with the use of spontaneous chemical reactions to produce electricity but also with the use of electricity to drive non-spontaneous reactions forward. Electrochemistry also provides techniques for monitoring chemical reactions and measuring properties of solutions such as the pK, of an acid. 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. 

In a galvanic cell, a spontaneous chemical reaction draws electrons into the cell through the cathode, the site of reduction, and releases them at the anode, the site of oxidation. 

Self-Test 12.5B (a) Write the chemical equation for the reaction corresponding to the cell Hg(l) Hg2Cl2(s) HCl(aq) Hg2(NO )2(aq) Hg(l). (b) Given that the cell emf is reported as positive, is the cell reaction spontaneous as written ... 

Redox reactions that have a positive Gibbs free energy of reaction are not spontaneous, but an electric current can be used to make them take place. For example, there is no common spontaneous chemical reaction in which fluorine is a product, and so the element cannot be isolated by any common chemical reaction. It was not until 1886 that the French chemist Henri Moissan found a way to force the... 

Although thermodynamics can be used to predict the direction and extent of chemical change, it does not tell us how the reaction takes place or how fast. We have seen that some spontaneous reactions—such as the decomposition of benzene into carbon and hydrogen—do not seem to proceed at all, whereas other reactions—such as proton transfer reactions—reach equilibrium very rapidly. In this chapter, we examine the intimate details of how reactions proceed, what determines their rates, and how to control those rates. The study of the rates of chemical reactions is called chemical kinetics. When studying thermodynamics, we consider only the initial and final states of a chemical process (its origin and destination) and ignore what happens between them (the journey itself, with all its obstacles). In chemical kinetics, we are interested only in the journey—the changes that take place in the course of reactions. 

---