During this period, Danes Thomson and Betro tried to explain the directionality of chemical reaction from the thermal effect of chemical reaction. They believe that the heat of reaction is a measure of the chemical affinity of reactants, and every simple or complex pure chemical action is accompanied by the generation of heat. Betro expounded the same viewpoint more clearly, and called it "the maximum working principle". He believes that any pure chemical change that is not affected by external energy will be carried out in the direction of producing substances that release the most energy. Although he found that some endothermic reactions can also be carried out spontaneously, he subjectively assumed that they were accompanied by exothermic physical processes. This erroneous assertion was finally admitted by him in 1930s, when he limited the application scope of "maximum work principle" to the reaction between solids and put forward the concept of chemical heat which is actually "free enthalpy". Horstmann, Le Chatterley and Van Hof also contributed in this respect. First of all, in the process of studying the sublimation of ammonium chloride, horstmann found that there is a certain relationship between decomposition pressure and temperature in the thermal decomposition reaction, which accords with Clausius-krabbe Dragon equation: dp/dt=Q/T(V'-V).
Where q represents the decomposition heat, and v and v' represent the total volume before and after decomposition. Van Hof derived the following formula from an equation:
lnK=-(Q/RT)+c
This formula can be applied to any reaction process, where q represents the heat of absorption (i.e. the heat of sublimation) of the system. Van Hof called the above formula the principle of dynamic equilibrium and explained it. He said that any balance between two different states of matter moves towards the balance of two systems, which generate heat due to temperature drop. In 1874 and 1879, Marty and Robin also put forward this principle respectively. Mudier suggested that the increase of pressure is beneficial to the corresponding reduction of volume. Later, Le Chatterley gave a further general explanation of this principle. He said that any system in chemical equilibrium will be transformed in one direction due to the change of a certain factor in the equilibrium. If this transformation is unique, it will cause a change opposite to the sign of this factor.
However, it is Gibbs who has made outstanding contributions in this respect, and his position in the history of thermochemistry is extremely important. Gibbs' contribution to mechanochemistry can be summarized in four aspects. First, on the basis of the second law established by Clausius and others, Gibbs derived the judgment basis of equilibrium state and correctly limited the judgment basis of entropy to the range of isolated systems. It makes it possible to deal with general practical problems. Secondly, internal energy, entropy and volume are used instead of temperature, pressure and volume as variables to describe the system state. It is pointed out that Thomson's description of system state by temperature, pressure and volume is incomplete. He advocated the equation of state that scientists were not familiar with at that time, and gave a complete surface describing all thermodynamic properties of the system in the three-dimensional coordinate diagram of internal energy, entropy and volume. Thirdly, Gibbs introduced the variable "concentration" into thermodynamics, and defined the derivative of component concentration to internal energy as "thermodynamic potential". In this way, thermodynamics can be used to deal with multi-component and multi-phase systems, and the problem of chemical equilibrium has the conditions for treatment. Fourthly, he further discussed the balance of the system under the influence of electricity, magnetism and surface. Moreover, he deduced the simplest, most essential and most abstract thermodynamic relationship in thermodynamics, namely the phase law, and the equilibrium state is the state with zero degree of freedom expressed by the phase law.
Gibbs' research results on balance are mainly published in his three articles. 1873, he published the first two articles in the Journal of Connecticut College, which immediately attracted Maxwell's attention. Gibbs' first two articles can be said to be just a foreshadowing. In 1876 and 1878, the third article, On the Equilibrium of Multiphase Substances, was published, which was more than 300 pages long and included more than 700 formulas. The first two articles discuss a single chemical substance system, and this article discusses a multi-component multiphase system. Due to the introduction of thermodynamic potential, the problem of multi-component system can be dealt with as long as the state equation of single-component system is changed slightly. For Gibbs' work, Le Chatterley thinks it is a new field, and its importance can be compared with the law of mass immortality. However, after the publication of Gibbs' three articles, their great significance has not been recognized by most scientists. It was not until 189 1 that ostwald translated them into German. 1899 After the publication of Chatterley, the situation suddenly changed. After Gibbs, thermodynamics can only deal with ideal systems. At this time, American Lois published articles in 190 1 and 1907 respectively, and put forward the concepts of "fugacity" and "activity". Louis talked about the concept of "escape trend" and pointed out that some thermodynamic quantities, such as temperature, pressure, concentration and thermodynamic potential, are all scales to measure escape trend.
The concepts of fugacity and activity put forward by Louis have made Gibbs' theory a useful supplement and development, thus making it possible for people to unify the deviation of the ideal system and making the actual system have exactly the same thermodynamic relationship with the ideal system in form.
The symbol of chemical equilibrium can be summarized as "one class and five invariants". Taking mA(g)+nB(g)==pC(g)+qD(g) as an example, this paper transforms abstraction into concreteness to improve students' understanding of this symbol. 1. First-class "first-class" means that the reaction rate is equal to the reverse reaction rate, which refers to the same reactant (or product) in the reaction system, rather than different substances in the same reaction. If different substances in the same reaction are used to represent the positive reaction rate and the reverse reaction rate, it must be required that the two rates are opposite (one-way rate is forbidden) and the ratio of the two rates is equal to the ratio of their corresponding stoichiometry. There are several specific forms in the test questions: (1) The positive reaction rate of the same substance is equal to the reverse reaction rate, such as υA (consumption) =υA (generation) or υD (consumption) =υD (generation). (2) The ratio of the positive reaction rate of one reactant to the reverse reaction rate of another reactant is equal to the stoichiometric ratio, such as υA (consumption): υB (generation) = m: n, or υC (consumption) :υD (generation) = p:q(3) The positive reaction rate of one reactant and the reverse of one product. 2. "Five invariants" means that the concentration of each component in the reaction mixture remains unchanged, that is, the amount of substances in each component remains unchanged; The concentration of each component is unchanged; The percentage content of each component remains unchanged; The conversion rate of reactants is unchanged; For all-gas reversible reaction, when m+n╪p+q, the amount of total substances in the mixed gas remains unchanged. The test questions have the following specific forms: (1) The amount of substances in each component remains unchanged, such as the number of molecules of A, B, C and D in a closed container at a certain temperature. (2) The concentration of each component is constant. If the external conditions remain unchanged, the color of the mixed gas will not change with time for the reversible reaction in which colored substances participate or generate. (3) The percentage content of each component remains unchanged, for example, the volume fraction, quantity fraction and mass fraction of each component remain unchanged. (4) The conversion rate of reactants is unchanged, for example, under certain conditions, the conversion rate of A or B will not change. The above items are not only applicable to reversible reactions in which the sum of gas stoichiometry is not equal before and after the reaction, but also applicable to reversible reactions in which the sum of gas stoichiometry is equal before and after the reaction. 5] For the reversible reaction in which the stoichiometry changes before and after all gases participate, the total amount of mixed gases remains unchanged. For example, when m+n╪p+q, the total pressure of the system is constant at a constant temperature and volume; When m+n╪p+q, the total volume of the system is constant at constant temperature and pressure; When m+n╪p+q, the average relative molecular mass of the mixed gas remains unchanged at a constant volume. Second, the special symbol of chemical balance. Under the condition of constant volume, can the density of mixed gas be used as a sign of chemical balance? This mainly depends on whether there are gaseous substances involved or generated in the reversible reaction. Because the gas density under this condition is only related to the gas quality, if all gaseous substances participate in the reversible reaction, under the condition of constant volume, the total mass of the mixed gas will not change, and the density of the mixed gas will not change, so it can not be used as a criterion to judge the chemical equilibrium state. If there is a reversible reaction involving non-gaseous substances, the total mass of the mixed gas will not change and the density of the mixed gas will not change only when the volume is constant, and then the density can be used as a criterion to judge the chemical equilibrium state.