Favourable change

You can easily predict what will happen in a number of physical and chemical processes. What will happen if you let go of a pencil that you are holding tip-down on a table What will you observe if you add a few drops of food colouring to some water in a glass If a piece of paper starts to burn in a plentiful supply of air, what are the products of the reaction How will an iron nail change if it is left outside These are all examples of favourable (or spontaneous] changes. A favourable change is a change that has a natural tendency to happen under certain conditions. 

Certainly many favourable physical and chemical changes are exothermic. Some favourable changes, however, involve no release of energy. Others are actually endothermic. For example, a favourable endothermic chemical reaction occurs when barium hydroxide and ammonium thiocyanate are placed in an Erlenmeyer flask, as shown in Figure 7.4. 

If the gas is ideal, this favourable change involves no change in energy. Why must the gas he ideal ... 

The process shown in Figure 7.5 is certainly a favourable change. Yet no exchange of energy is involved. The condition that influences this change is called entropy. It is an important condition in all physical and chemical changes. 

What does entropy have to do with favourable chemical changes and equilibrium systems All favourable changes involve an increase in the total amount of entropy. Recall the endothermic reaction in Figure 7.4. 

Now recall the reaction between mercury and oxygen. It favours the formation of HgO below about 400°C, but the decomposition of HgO above 400°C. This reaction highlights the importance of temperature to favourable change. Enthalpy, entropy, and temperature are linked in a concept called free energy. 

HRT has also been shown to cause favourable changes in serum lipid levels in normal postmenopausal women [13]. This effect could be particularly beneficial in women with cholestatic liver disease who may have elevated serum cholesterol. 

Apart from protection against osteoporosis, HRT is also associated with favourable changes in serum lipid levels in postmenopausal women. This may be helpful in this patient, who has fatty liver disease. 

The complementary use of CO and NO as probe molecules allowed us to obtain information on the nature and dispersion of the Pt and/or Cu supported phases and on the effect of the pre-calcination temperature of the hydrotalcite support. The influence of the sample pre-treatment was also taken into account in view of the catalytic applications of these materials in the NOx storage-reduction process, which involves an alternation of oxidisit or reducing steps. We would just underline that the formation of a bimetallic phase evidenced in the case of the catalysts containing Pt and Cu can be particularly interesting from a catalytic point of view. Indeed, the modification observed in the metal properties due to the alloying can induce favourable changes in the specific activity and selectivity of the catalysts. 

Chitosan and its derivatives induce favourable changes in the metabolism of plants and fruits. This results in an increased germination and higher crop yields [176,179]. 

Lee, J. W., Lee, H. R., Shim, J. Y. et al. 2008. Abdominal visceral fat reduction is associated with favourable changes of sernm retinol-binding protein 4 in nondiabetic subjects. Endocrine J 55 811-818. 

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