Interpretation: Whether the given statement is true for the calculation of standard enthalpy change of the reaction at 500 K or not needs to be determined.
Concept Introduction:
Enthalpy change of a reaction is the amount of heat absorbed or evolved during the reaction which takes place at constant pressure conditions The standard enthalpy change for a reaction
i.e.
Here,np and nr are the number of moles of the products and reactants
Answer to Problem 4.1CP
The given statement is not true, since heat capacities of the substances involved in the reaction needs to be included at T = 500K
Explanation of Solution
Based on Kirchhoff's law the change in enthalpy (ΔH) of a reaction is directly proportional to the change in temperature (ΔT) i.e.
Where Cp is the heat capacity at constant pressure.
Equation (1) holds true only if the reaction takes place at 298K. At any other temperature, the heat capacities of the products and reactants need to be included. As a result, the net equation becomes:
Where ΔCp is the difference in the heat capacities of the products and reactants
In order to calculate the enthalpy change of the reaction at 500 K (or any temperature other than 298 K), heat capacities of the substances involved in the reaction needs to be included.
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