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Measuring Change in Internal Energy and Change in Enthalpy

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Measuring Change in Internal Energy and Change in Enthalpy - Lesson Summary

Calorimetry is an experimental technique that involves the measurement of heat changes associated with physical (or) chemical processes.

The experimental technique of Calorimetry actually involves two steps.

  • The determination of heat capacity of a calorimeter.
  • Involves the determination of the change in temperature during the completion of the reaction.

The measure of a bomb calorimeter's heat absorbing property is called its heat capacity.

Heat produced:
         qv = Cv x ΔT
                       Cv = heat capacity of the calorimeter

Molar heat of combustion = Cv x ΔT x M/W

Where , W = mass of the substance (in grams)
            M = Molecular weight of that substance (in grms)

              qv = ΔU (Internal Energy Change)

Heat evolved is the heat of combustion at constant volume and is a measure of internal energy change ∆U.

In an exothermic reaction, heat is evolved and the system loses heat to the surroundings. Therefore enthalpy change ∆H is negative.

In an endothermic reaction, heat is absorbed by the system, from the surroundings and therefore, the enthalpy change ∆H will be positive.


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