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Van 't Hoff plot for an endothermic reaction. For an endothermic reaction, heat is absorbed, making the net enthalpy change positive. Thus, according to the definition of the slope: =, When the reaction is endothermic, Δ r H > 0 (and the gas constant R > 0), so
If the net enthalpy change is negative (<), the reaction is exothermic and is more likely to be spontaneous; positive ΔH values correspond to endothermic reactions. ( Entropy also plays an important role in determining spontaneity, as some reactions with a positive enthalpy change are nevertheless spontaneous due to an entropy increase in the ...
Whether a process can occur spontaneously depends not only on the enthalpy change but also on the entropy change (∆S) and absolute temperature T.If a process is a spontaneous process at a certain temperature, the products have a lower Gibbs free energy G = H – TS than the reactants (an exergonic process), [2] even if the enthalpy of the products is higher.
The thermite reaction is famously exothermic. The reduction of iron(III) oxide by aluminium releases sufficient heat to yield molten iron. In thermochemistry, an exothermic reaction is a "reaction for which the overall standard enthalpy change ΔH⚬ is negative." [1] [2] Exothermic reactions usually release heat.
Enthalpy is the transfer of energy in a reaction (for chemical reactions, it is in the form of heat) and is the change in enthalpy. Δ H {\displaystyle \Delta H} is a state function, meaning that Δ H {\displaystyle \Delta H} is independent of processes occurring between initial and final states.
According to the IUPAC, an exothermic reaction is "a reaction for which the overall standard enthalpy change ΔH⚬ is negative". [4] Some examples of exothermic process are fuel combustion, condensation and nuclear fission, [5] which is used in nuclear power plants to release large amounts of energy. [6]
Enthalpy of mixing can often be ignored in calculations for mixtures where other heat terms exist, or in cases where the mixture is ideal. [2] The sign convention is the same as for enthalpy of reaction: when the enthalpy of mixing is positive, mixing is endothermic, while negative enthalpy of mixing signifies exothermic mixing. In ideal ...
Endothermic reactions absorb heat, while exothermic reactions release heat. Thermochemistry coalesces the concepts of thermodynamics with the concept of energy in the form of chemical bonds. The subject commonly includes calculations of such quantities as heat capacity, heat of combustion, heat of formation, enthalpy, entropy, and free energy.