Entropy physical change

In many physical changes, the entropy increase is the major driving force. This situation applies when two liquids with similar intermolecular forces, such as benzene (C6H< ) and tol-... 

The second law of thermodynamics states that the total entropy of a chemical system and that of its surroundings always increases if the chemical or physical change is spontaneous. The preferred direction in nature is toward maximum entropy. Moving in the direction of greater disorder in an isolated system is one of the two forces that drive change. The other is loss of heat energy, AH. 

Two factors determine the spontaneity of a chemical or physical change in a system a release or absorption of heat (AH) and an increase or decrease in molecular randomness (AS). To decide whether a process is spontaneous, both enthalpy and entropy changes must be taken into account ... 

Although chemists deal primarily with the chemical changes of matter, physical changes are also very important. In this section we will consider how the entropy of a substance depends on its temperature and on its physical state. 

Energy, Enthalpy, and Entropy Changes Involving Ideal Cases and Physical Changes... 

The changes of the activation energy and activation entropy around the glass transition temperature listed in Tables 5 and 6 are of such importance that they can only be interpreted on the basis of physical changes of the polymeric environment, i.e. an important increase of the chain segment mobility and consequently of the free volume above Tg. The additional increase of the activation energy has to be related with the Ea of viscous flow of the polymer. 

Describe the change in entropy of the following chemical and physical changes, using the information on pages 716 and 717. a) Wood burns and forms carbon dioxide and water vapor, b) Dry ice sublimes at room temperature and forms carbon dioxide gas. c) Liquid oxygen freezes. 

The following example deals with the entropy changes of a system resulting from physical changes. 

Both enthalpy (A//) and entropy (A5) changes are important in determining chemical and physical equilibrium, and this is particularly the case in biomolecular systems dominated by non-covalent interactions, where the intermolecular forces are relatively small and comparable to entropic effects arising from molecular dynamics and solvation changes. 

Entropy change A measure of the change in fhe disorder of a system as it undergoes chemical reaction or physical change... 

Physical properties of substance close to N-1 phase transition may be related to the parameters of Landau expansion [8]. For example we can calculate an entropy density change at the transition temperature Tc from Eq. 6.9 and Sc = BI3C ... 

The key concept of entropy as an assessment of dispersal of matter and of energy is carefully developed to provide a firm foundation for later ideas including heat changes that accompany chemical and physical changes, prediction of reactions, and chemical bond stability. Throughout this chapter, many fundamental terms are rigorously defined, discussed, and illustrated for use throughout later studies of chemistry. 

The attractive force can be quite large for a polar solvent molecule in direct contact with an ion. This is part of the large exergonic physical change when solid salts dissolve in water. The entropy of mixing also favors dissolution (see Section 3.1.5). Table 3.6 shows several heats of hydration (equivalent to the heat of solution for water as solvent) for various ions, salts, and a few organic structures. 

The second law of thermodynamics states that the total entropy of the universe tends to increase. This usually means that for a chemical reaction or a physical change to take place, the entropy of the system (the reactants) and their surroundings must increase. Some chemical reactions and physical changes appear to have a decrease in entropy but this is because the entropy of the surroundings increases by a greater amount, giving an overall increase in entropy in the universe (Figure 15.31). The system is the sample or reaction mixture. Outside the... 

Chemical reaction or physical change Entropy change Example... 

Table 15.5 Qualitative entropy changes (of the system) for some common reactions and physical changes...

Chemists want to know whether a physical change or chemical reaction is spontaneous under standard conditions (1 atm pressure and 298 K). A spontaneous process has a natural tendency to occur. A spontaneous process involves an increase in the entropy of the universe. 

The forces on atoms and molecules can be described in terms of two tendencies. Molecules react, change conformations, bind, and undergo other chemical or physical changes in ways that cause a quantity called the energy to reach its minimum possible value, or a quantity called the entropy to reach its maximum possible value. We can predict the tendencies of matter by computing the minima or maxima of certain mathematical functions. These are called extremum (or variational) principles. 

Entropy determines the direction of chemical and physical change. A chemical system proceeds in a direction that increases the entropy of the universe—it proceeds in a direction that has the largest number of energetically equivalent ways to arrange its components. 

All physical processes occur with an increase in entropy when changes in both the system and the surroundings are considered. When no further spontaneous change is possible, the total entropy has increased to a maximum, and the system is at equilibrimn (Figme 2). 

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