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In chemistry, Le Chatelier's principle (pronounced UK: / l ə ʃ æ ˈ t ɛ l j eɪ / or US: / ˈ ʃ ɑː t əl j eɪ /) [1] is a principle used to predict the effect of a change in conditions on chemical equilibrium. [2] Other names include Chatelier's principle, Braun–Le Chatelier principle, Le Chatelier–Braun principle or the equilibrium ...
Hess's law states that the change of enthalpy in a chemical reaction is the same regardless of whether the reaction takes place in one step or several steps, provided the initial and final states of the reactants and products are the same. Enthalpy is an extensive property, meaning that its value is proportional to the system size. [4]
The Van 't Hoff equation relates the change in the equilibrium constant, K eq, of a chemical reaction to the change in temperature, T, given the standard enthalpy change, Δ r H ⊖, for the process. The subscript r {\displaystyle r} means "reaction" and the superscript ⊖ {\displaystyle \ominus } means "standard".
Hess's law states that the sum of the energy changes of all thermochemical equations included in an overall reaction is equal to the overall energy change. Since Δ H {\displaystyle \Delta H} is a state function and is not dependent on how reactants become products as a result, steps (in the form of several thermochemical equations) can be used ...
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods to the ...
[1] [2] [3] A more fundamental statement was later labelled as the zeroth law after the first three laws had been established. The zeroth law of thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature: if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium ...
Hess' law of constant heat summation (1840): The energy change accompanying any transformation is the same whether the process occurs in one step or many. [3] These statements preceded the first law of thermodynamics (1845) and helped in its formulation. Thermochemistry also involves the measurement of the latent heat of phase transitions.
The zeroth law is of importance in thermometry, because it implies the existence of temperature scales. In practice, C is a thermometer, and the zeroth law says that systems that are in thermodynamic equilibrium with each other have the same temperature. The law was actually the last of the laws to be formulated. First law of thermodynamics