Effect of Temperature on Reaction Enthalpy

If we know the enthalpy change for a reaction at one temperature, the heat capacities of the reactants and products can be used to determine the heat capacity at a different temperature.

[@manavpandey3133]

Very helpful.......thanks

[@PhysicalChemistry]

I'm glad it was useful

[@amitpandey5370]

Thank you sir 😊😊

[@PhysicalChemistry]

You're very welcome

[@vasuagrawal6697]

helpful 😀

[@debarghapaul866]

Does enthalpy of reaction being defined at a particular temperature how imply that a reaction is somehow an isothermal process?

[@PhysicalChemistry]

No, definitely not. You can do the reaction any way you want: isothermally, adiabatically, isochorically, etc. But when we say that we want the reaction enthalpy at 298 K, it just means that the reactants have to start at 298 K and end at 298 K. You just have to include the enthalpy of heating/cooling the reactants and products to 298 K if you start/finish with them at some different temperature. Your question gets at the heart of the difference between state functions and path functions. The products at 298 K is one state. The reactants at 298 K is another state. Because enthalpy is a state function, the enthalpy change is the difference between these two enthalpies -- regardless of what path you take to get there! The freedom this gives you is a huge convenience.

[@debarghapaul866]

@@PhysicalChemistry Thanks for the clarification

[@camillestevenson5456]

Because when H2O (g) is cooled from 700K to 298 K H2O (l) there is a phase change, is there an additional heat value for the heat of vaporization as water changes from a gas to water? Whereas there is no phase change for CO and CO2 from 700K to 298 K so there is no additional heat associated with a phase change?