Info

Phase transition properties 0.000°C

mm Hg) 6.012 kJ (1.436 kcal)/mol 40.63 kJ (9.705 kcal)/mol

50.91 kJ (12.16 kcal)/mol at constant pressure, which is the case in most food processing:

Often in a food process, there is no pv work so that the change in internal energy is equal to the change in enthalpy.

The specific heat of a food is the change in heat content per unit mass per unit temperature change. At constant volume

T2 - Tx and at constant pressure

Cp Avg.

In actuality, specific heat is not constant over significant temperature and pressure ranges and each of the above equations must be considered in integral form for precise definitions. However, over most ranges of temperature and pressure at which food process and auxiliary food operations take place, the specific heats can be considered constant and the average value is satisfactory.

Entropy (S) expresses the second law in precise mathematical terms. The first law is concerned with the accounting of the many kinds of energy that are involved in a given process whereas the second law is concerned with how available the energy of this system is for doing useful work. The concept of entropy is hard to visualize since it is not defined in terms which one can equate to normal physical entities such as a mass of material or a given amount of heat. It is expressed as follows:

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