Thermochemistry is a branch of physical chemistry.To study the laws of thermal effects in the process of physical and chemical changes.withFirst law of thermodynamicsIs based on.It is an important experimental method to measure the thermal effect directly in a calorimeter.Thermochemical data (such as combustion heat, generation heat, etc.) are widely used in thermodynamic calculation, engineering design and scientific research, safety engineering, etc.[1]
ThermochemistryThermochemistry has played an important role in the development of physical chemistry.In modern times, due to the progress of science and technology, the calorimetric method has been improved, especially the improvement of thermal measurement accuracy. Thermochemistry is still of great significance in the fields of fuel, food, biology and medicine.Thermochemical data (such as combustion heat, generation heat, etc.)Thermodynamic calculation, engineering design and scientific research, etc.Thermochemistry, the study of the laws of thermal effects in physical and chemical processes.It is a branch of chemistry and the application of heat in physics in chemistry.
Laws
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Thermochemical dehydrator
yesnatureIt is a universal law ofexperimentIt is also called,EngelsHailed it as the 19th centurynatural scienceOne of the three decisive discoveries in.thisLawsThe main contents of are:energyThere are various forms, which can be transformed from one form to another, and transferred from one object to another. In the transformation and transmission, the value of energy remains unchanged.holdFirst law of thermodynamicsSpecifically applied tochemical reactionUp, usingexperimentDetermination and calculation of chemical reactionquantity of heatThe science that studies this aspect is called thermochemistry.
Note that the thermal effect of chemical reaction must meet the following conditions:
(a) The temperature of the product is the same as that of the reactant, and the heat change caused by the increase or decrease of the product temperature shall not be mixed into the reaction heat.
QP=∆ H, that is, in the process of constant pressure reaction, all the heat absorbed by the system is used to change theEnthalpy, its establishment must meet three conditions
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Thermochemical reaction formula
Thermochemistry is mainly researchchemical reactionThe heat conversion problem in.In addition to exchanging energy with the external environment in the form of heat, chemical reactions often exchange energy in the form of work.For example, gunpowder explosion producesExpansion work，Chemical batterystayemfConveying under actionchargeForElectric powerEtc.As mentioned in this section, "in chemical reactions, material changes are accompanied by energy changes, which are oftenheat energyIn the form of ".Here, "often" means that energy is exchanged in the form of work in addition to heat.It should be pointed out thatchemical reactionUnder certain conditionsExpansion work, instead ofNonexpansive work(as electrical work).
Thermochemical vapor deposition refers to the use ofsubstrateSurface heatcatalysisBy means ofChemical vapor deposition。The deposition temperature of this method is relatively high, generally around 800 ℃~1200 ℃high temperatureThe selection of substrate is greatly limited, but it isChemistryThe classic method of vapor deposition.
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First Law and Thermochemistry
Thermodynamic temperature, also called thermodynamic standard temperature, symbol T, unit K（Kelvin, referred to as open).As early as 1787, FrancephysicsJ. Charles found that when the pressure is constant and the temperature increases by 1 ℃, the volume increase (expansion rate) of a certain amount of gas is a fixed value,Volumetric expansionRate versus temperaturelinear relationship。At first, the fixed value was 1/269 of the volume of gas at 0 ℃. Later, after decades of experimental correction by many people, especially the work of the French J.L. Gay Lussac in 1802, the value was finally determined to be 1/273.15.The relationship between the above gas volume and temperature is expressed by the formula as follows:
V=V0（1+t/273.16）=V0（t+273.15）/273.15
law of thermochemistry
Where V isCelsius temperatureIs the gas volume at t/℃.If t+273.15 ∨ T is defined (then 0+273.15=T0, unit: K), the above relationship can be expressed by a simpler formula: V/T=V0/T0,V1/T1=V0/T0，V2/T2=V0/T0,……，Naturally, V1/T1=V2/T2, that is, at any temperature, a certain amount of gas, at a certain pressure, the volume V and T of the gas areTemperature scaleThe temperature is inversely proportional.This is Charlie Guy LussacLaws。In fact, this relationship only applies toideal gas。For this reason, people first called T the ideal gas temperature (temperature scale), also calledAbsolute temperature(temperature scale).After the formation of thermodynamics, it is found that the temperature scale has more profoundPhysical meaning, especiallyClausius(Clausius) andKelvin（Kelvin）DemonstratedAbsolute zeroInaccessible, renamedThermodynamic temperature(temperature scale), and use the first letter K of Kelvin as its unit.The temperature of an object is the movement of a large number of particles that make up the object（Thermal movement）The macro embodiment of the intensity of.For example, byMonatomic moleculeThe average of a large number of molecules of gaskinetic energyEk and its temperature TStatistical thermodynamicsThe theoretical derivation is as follows:
E(—)k=3/2kT
Where k=1.381 × 10-23J/K, calledBoltzmann(Boltzmann) constant, equal togas constant The ratio of R to Avogadro constant N0.
