1 PH E Tampoes

pH e Tampões

Bioquímica

Nina Marí G. P. de Queiroz [e-mail] Entropia
É a propriedade TD para medir a energia não utilizável durante a realização de um trabalho em termodinâmica

Spontaneous change
Is a change that will occur naturally, without external intervention. In relation to chemical reactions, reactions that occur naturally will often release energy, as so are exothermic.
This makes sense since energy is released as most stable products are formed. However, some spontaneous reactions are endothermic, so there must be another factor we need to consider. This factor is entropy. Entropy is the degree of disorder there is in a system. If there is more disorder in a system, there will be a higher value of entropy (S). The disorder of a system is very closely linked to the phase it is in.

If you take the above example of a jar of bromine and next to an empty jar; when the divider between the two of them is removed, the bromine will fill both jars evenly. But why doesn't it fill the other entirely? It is because there are many more probabilities of there being an even distribution than not, ie. it will spontaneously diffuse evenly.

Entropy is affected by temperature. This is shown in the diagram below. Entropy increases gradually with temperature, but then there is a sudden jump when the phase changes, and the biggest jump occurs from liquid to gas. This is because there are more ways of arranging a gas than a liquid. Ions and molecules in solution also have higher entropy.

Calculating entropy change simply requires you to use given entropy values for particular substances and use the following equation. They have the units J K-1 mol-1. It is possible to have absolute entropy since at 0 Kelvin, there is no entropy.

Feasibility of Reactions
As discussed above, reactions that are exothermic happen quite easily, and reactions that are endothermic but result in an increase in disorder are also likely to happen. Therefore it is possible
to