Internal energy of a body

The first law of thermodynamics states that the change in the internal energy of a body equals the work done by the external forces plus the change in heat. In a more detailed form and for unit volume it is written as... 

The internal energy of a body is the sum of the potential energy and the kinetic energy of its component atoms and molecules. 

The symbol U designates the total internal energy. Our present state of knowledge does not allow us to measure the total internal energy of a body, but we can measure the energy change involved in a physical transition, thus in the process of melting,... 

The internal energy U is defined as the total energy of a body s components. Unfortunately, there is no way of telling how much energy is locked away. In consequence, the experimentalist can only look at changes in U. 

Hence, we arrive at the conclusion that only in the limit a - 0 the Hookean body is the ideal energy-elastic one (r = 0) and the uniform deformation of a real system is accompanied by thermal effects. Equation (19) shows also that the dependence of the parameter q (as well as to) on strain is a hyperbolic one and a, the phenomenological coefficient of thermal expansion in the unstrained state, is determined solely by the heat to work and the internal energy to work ratios. From Eqs. (17) and (18), we derive the internal energy of Hookean body... 

The convection heat loss from the body is evidenced as a decrease in the internal energy of the body, as shown in Fig. 4-2. Thus... 

If he volume of a mass of gas is varied while its temperature is kept constant, the internal energy of this body undergoes no change in value. 

The internal energy of a system or body (for example, a unit of air volume) with well-defined boundaries, denoted by U, is the total kinetic energy due to the motion of particles (translational, rotational and vibrational) and the potential energy associated with the vibrational and electric energy of atoms within molecules or any matter state. This includes the energy in all chemical bonds and that of free electrons (for example, hydrated electrons in water and photons in air). 

This is equal to the heat absorbed, since the internal energy of a perfect gas remains constant at constant temperature. The entropy change of the gas is therefore 1.16 x 10 300=38.3 J K . The corresponding entropy change of the body which supplies the heat is — 38.3 JK"> and the overall entropy change is zero. 

The first law of thermodynamics states that in an energetically isolated body the total energy remains constant during any change that may occur in it . It follows that if an amount of heat A( is absorbed by a body and that work A is also done on it there will be a change in internal energy of that body At/, viz ... 

Here e is the internal energy per unit mass, and s is the entropy per unit mass. The first axiom indicates that the rate of change of internal and kinetic energy of a body is caused by the heat that is supplied to the body and the work that is done on the body. The second axiom indicates that the internal energy is a function of the local state of the system. 

Eq. (3.4.3) enables us to define the internal energy of the system from a thermodynamic position only internal energy is a body property, the change of which is equal to the difference of heat brought into the system and the work produced against external forces. 

Heat is one of the many forms of energy and mainly arises from chemical sources. The heat of a body is its thermal or internal energy, and a change in this energy may show as a change of temperature or a change between the solid, liquid and gaseous states. 

Reaction 9.133 represents an alternate fate for C, in which collision with a third body M carries away (as translational energy) excess internal energy of C, leaving behind a stable C molecule. This so-called stabilization reaction, with rate constant ks, provides an alternate product-formation channel. The reactive intermediate C can also react via 9.134, the main channel to form products D and E. This reaction channel proceeds with rate constant kr. 

The heat capacity of a body is defined as the amount of heat required to increase the temperature of the body 1 K. The heat capacity itself may depend on temperature, but we will ignore this complication. For the same reasons that we distinguish between internal energy and enthalpy,... 

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