Chemical reactions definition

The driving force for chemical reactions definition of affinity... 

The are many ways to define the rate of a chemical reaction. The most general definition uses the rate of change of a themiodynamic state function. Following the second law of themiodynamics, for example, the change of entropy S with time t would be an appropriate definition under reaction conditions at constant energy U and volume V ... 

For non-zero and the problem of defining the thennodynamic state fiinctions under non-equilibrium conditions arises (see chapter A3,2). The definition of rate of change implied by equation (A3,4,1) and equation (A3.4.2) includes changes that are not due to chemical reactions. 

The key to experimental gas-phase kinetics arises from the measurement of time, concentration, and temperature. Chemical kinetics is closely linked to time-dependent observation of concentration or amount of substance. Temperature is the most important single statistical parameter influencing the rates of chemical reactions (see chapter A3.4 for definitions and fiindamentals). 

Chemists usually learn about reactions according to fiinctional groups for example, How can I make an aldehyde and what reactions are known for aldehydes " This is clearly not a very good starting point for classifying reactions. The poor state of affairs in the definition of reaction types is further quite vividly illustrated by the fact that many chemical reactions are identified by being named after their inventor Diels-Alder reaction, Michael addition, Lobry-de Bruyn-van Ekenstein rear-... 

Normality makes use of the chemical equivalent, which is the amount of one chemical species reacting stoichiometrically with another chemical species. Note that this definition makes an equivalent, and thus normality, a function of the chemical reaction in which the species participates. Although a solution of 1T2S04 has a fixed molarity, its normality depends on how it reacts. 

A catalyst is a substance that iacreases the rate of approach to equiUbrium of a chemical reaction without being substantially consumed itself. A catalyst changes the rate but not the equiUbrium of the reaction. This definition is almost the same as that given by Ostwald ia 1895. The term catalysis was coiaed ia ca 1835 by Ber2eHus, who recognized that many seemingly disparate phenomena could be described by a single concept. For example, ferments added ia small amounts were known to make possible the conversion of plant materials iato alcohol and there were numerous examples of both decomposition and synthesis reactions that were apparendy caused by addition of various Hquids or by contact with various soHds. 

It is important to understand that when chemical reactions are involved, this definition of Cl is based ou the driving force defined as the difference between the couceutratiou of un reacted solute gas at the interface and in the bulk of the liquid. A coefficient based ou the total of both uureacted and reached gas could have values. smaller than the physical-absorption mass-transfer coefficient /c . 

For fast chemical reactions the reactant A is by definition completely consumed in the thin film near the hquid interface. Thus, x = 0, and... 

Chemical engineering inherited the definition for the reaction rate from chemical kinetics. The definition is for closed systems, like batch reactors, in which most of the classical kinetic studies were done. Inside a batch reactor little else besides chemical reaction can change the concentration of reactant A. In a closed system, for the reaction of... 

At the First European Symposium on Chemical Engineering, Amsterdam, (1957) the definition for Chemical Reaction Engineering was accepted as ... 

The chemical reactions that occnr in flames transform an initial reactant mixtnre into final reaction prodncts. In the case of fnel-oxygen combns-tion, the final prodncts are principally water vapor and carbon dioxide, althongh nnmerons other prodncts snch as carbon monoxide may be formed, depending on the reactant composition and other factors. If the ratio of fnel-to-oxygen is stoichiometric, the final reaction prodncts, by definition, contain no excess fnel or oxygen. Theoretically, this means that partial oxidation prodncts snch as CO (itself a fnel) are not formed. In reality, partial oxidation prodncts snch as CO or OH are formed by high tem-peratnre reactions. For example, the molar stoichiometric reaction of methane is written ... 

The rate of a chemical reaction can be described in any of several different ways. The most commonly used definition involves the time rate of change in tlie amount of one of the components participating in tlie reaction tliis rate is usually based on some arbitrary factor related to tlie reacting system size or geometry, such as volume, mass, or interfacial area. Tlie definition shown in Eq. (4.6.7), wliich applies to homogeneous reactions, is a convenient one from an engineering point of view. 

One molecule (or mole) of propane reacts with five molecules (or moles) of oxygen to produce three molecules (or moles) or carbon dioxide and four molecules (or moles) of water. These numbers are called stoichiometric coefficients (v.) of the reaction and are shown below each reactant and product in the equation. In a stoichiometrically balanced equation, the total number of atoms of each constituent element in the reactants must be the same as that in the products. Thus, there are three atoms of C, eight atoms of H, and ten atoms of O on either side of the equation. This indicates that the compositions expressed in gram-atoms of elements remain unaltered during a chemical reaction. This is a consequence of the principle of conservation of mass applied to an isolated reactive system. It is also true that the combined mass of reactants is always equal to the combined mass of products in a chemical reaction, but the same is not generally valid for the total number of moles. To achieve equality on a molar basis, the sum of the stoichiometric coefficients for the reactants must equal the sum of v. for the products. Definitions of certain terms bearing relevance to reactive systems will follow next. 

On the other hand, corrosion has been defined as the undesirable deterioration of a metal or alloy, i.e. an interaction of the metal with its environment that adversely affects those properties of the metal that are to be preserved. This definition —which will be referred to as the deterioration definition —is also applicable to non-metallic materials such as glass, concrete, etc. and embodies the concept that corrosion is always deleterious. However, the restriction of the definition to undesirable chemical reactions of a metal results in anomalies which will become apparent from a consideration of the following examples. 

A chemical reaction can occur only if — AG > 0, i.e. if — AG is positive in addition the value a = is by definition the maximum activity for a condensed component where the pure phase is taken as standard state, thus A/i is always negative. This discussion will be restricted to gases where p 1 taking p = 1 atm (101 325 kN/m ) as the standard state for the gas, X, it is evident that A/ix is always a negative quantity or zero. 

So far in this chapter our discussion has focused on thermochemistry, the study of the heat effects in chemical reactions. Thermochemistry is a branch of thermodynamics, which deals with all kinds of energy effects in all kinds of processes. Thermodynamics distinguishes between two types of energy. One of these is heat (q) the other is work, represented by the symbol w. The thermodynamic definition of work is quite different from its colloquial meaning. Quite simply, work includes all forms of energy except heat. 

The above definition of normal solution utilises the term equivalent . This quantity varies with the type of reaction, and, since it is difficult to give a clear definition of equivalent which will cover all reactions, it is proposed to discuss this subject in some detail below. It often happens that the same compound possesses different equivalents in different chemical reactions. The situation may therefore arise in which a solution has normal concentration when employed for one purpose, and a different normality when used in another chemical reaction. 

Cell growth and metabolic activities are similarly described as a simple chemical reaction. It is also necessary to establish a definite formula for dry cell matter. The elemental composition of certain strains of microorganism is defined by an empirical formula CHaO/3Ns. The general biochemical reaction for biomass production is based on consumption of organic substrate, as shown below. Substrate oxidation is simplified in the following biochemical oxidation ... 

When the cell is in action, a definite chemical reaction occurs in its interior, and according to Faraday s laws the amount of chemical decomposition is proportional to the quantity of... 

---