In chemistry, the standard enthalpy of reaction is the enthalpy change when reactants in their standard states (p = 1 bar, T = 298 K) change to products in their standard states. This quantity is the standard heat of reaction at constant pressure and temperature, and it can be measured by calorimetric methods in which the temperature does vary, provided that the initial and final pressure and temperature correspond to the standard state.

In food products enthalpy measurements are often used to test if proteins in products can be unfolded, which means that they are still in a somewhat native state.

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