System internal energy changes

Apphed to a closed system which undergoes only an internal energy change, the first law of thermodynamics is given by equation 1 ... 

In order to utilise our colloids as near hard spheres in terms of the thermodynamics we need to account for the presence of the medium and the species it contains. If the ions and molecules intervening between a pair of colloidal particles are small relative to the colloidal species we can treat the medium as a continuum. The role of the molecules and ions can be allowed for by the use of pair potentials between particles. These can be determined so as to include the role of the solution species as an energy of interaction with distance. The limit of the medium forms the boundary of the system and so determines its volume. We can consider the thermodynamic properties of the colloidal system as those in excess of the solvent. The pressure exerted by the colloidal species is now that in excess of the solvent, and is the osmotic pressure II of the colloid. These ideas form the basis of pseudo one-component thermodynamics. This allows us to calculate an elastic rheological property. Let us consider some important thermodynamic quantities for the system. We may apply the first law of thermodynamics to the system. The work done in an osmotic pressure and volume experiment on the colloidal system is related to the excess heat adsorbed d Q and the internal energy change d E ... 

In the case of an electrical calibration, at the beginning of the main period a potential V is applied to a resistance inside the calorimeter proper, causing a current of intensity / to flow over a period t. As a result, an amount of heat Q = Vlt is dissipated in the calorimeter proper, causing the observed temperature rise. If the calibration is carried out on the reference calorimeter proper (without contents ), then eci = ecf = 0 and the internal energy change of the calorimetric system during the main period is... 

The first law of thermodynamics simply says that energy cannot be created or destroyed. With respect to a chemical system, the internal energy changes if energy flows into or out of the system as heat is applied and/or if work is done on or by the system. The work referred to in this case is the PV work defined earlier, and it simply means that the system expands or contracts. The first law of thermodynamics can be modified for processes that take place under constant pressure conditions. Because reactions are generally carried out in open systems in which the pressure is constant, these conditions are of greater interest than constant volume processes. Under constant pressure conditions Equation 3 can be rewritten as... 

Suppose that a change in the system takes place at constant pressure and that during the change the internal energy changes by AU and the volume changes by AV. It then follows from the definition of enthalpy in Eq. 16 that the change in enthalpy is... 

Thus for a mechanically reversible, constant-volume, nonflow process, the heat transferred is equal to the internal-energy change of the system. 

We will now consider how the internal energy, /, changes when material enters or leaves a system. This will help us derive an expression for the Gibbs free energy that is quite useful for biological applications. 

For reversible changes in a system equation the entropy change of the system, dS y = dqlT. Considering first a system doing no external work—that is, only pV work, dw = p the internal energy change is given by... 

When applied to closed (constant-mass) systems in which only internal-energy changes occur, the first law of thermodynamics is expressed mathematically as... 

The internal energy change AC/ of a system is a sum of the heat flowing into it (Q) and the work done by the system (-W). Heat is defined as the energy transfer between the system... 

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