noobstuff.blogg.se - Whats entropy

In simpler words, entropy gives us an idea about that portion of energy that does not convert into work done and adds to the disorder of the system instead. the more is the spontaneity in a thermodynamic process, the higher is its entropy or the degree of disorder.

It helps redefine the second law of thermodynamics.Įntropy relates to spontaneity i.e. Entropy is an interesting concept as it challenges the belief of complete heat transfer. The entropy is denoted by ‘S’ and it is an extensive property because the value of entropy or Entropy Change is dependent on the substance present in a thermodynamic system. The term disorder denotes the irregularity or lack of uniformity of a thermodynamic system. This randomness could be in regards to the entire universe or a simple chemical reaction or something as simple as the heat exchange and heat transfer. So, let's understand this concept of entropy and the change in entropy.Įntropy is the measure of disorder or randomness. By this law, the entropy of the universe can never be negative. The second law of thermodynamics talks about the concept of entropy and tells that the entropy of the universe is always increasing. Three laws govern the science of thermodynamics and here we will discuss the second law of thermodynamics. It also deals with the work done for the conversion of energy from one form to another. If ∆ S total for a reaction is positive, the reaction will be feasible, if negative it will not be feasible.Thermodynamics is the study of the changes in energy associated with the change in temperature and heat. ∆ S total = ∆ S system + ∆ S surroundings So if we want to predict the direction of a chemical reaction we must take account of the total entropy change of the system and the surroundings, and that includes the effect on entropy of any heat change from the system to the surroundings (or in the other direction, heat taken in from surroundings to system). So the total entropy change (of the Universe, ie system + surroundings) brought about by the reaction is +307 J K ‑1 mol -1. ∆ S surroundings = 591 J K -1 mol -1, more than enough to outweigh the value of ∆S system of –284 J K ‑1 mol -1.

the same amount of energy dumped into the surroundings will make more difference at lower temperature – this rationalises the ‘division by T’įor the ammonia / hydrogen chloride reaction at 298 K:.

the more negative the value of ∆ H, the more positive the entropy increase of the surroundings.

the negative sign means that an exothermic reaction (∆ H is negative, heat given out) produces an increase in the entropy of the surroundings.

The formal derivation is complex but leads to the expression ∆ S of the surroundings (∆ S surroundings) = –∆ H / T. But how can we evaluate the entropy change caused by ‘dumping’ 176 kJ mol -1 of heat energy into the surroundings? (Notice that this is 176 000 J mol -1.) It must be positive as more quanta of energy lead to more possible arrangements and it must be more than 284 J K -1 mol -1.

It is negative as we have calculated (and predicted from the reaction being two gases going to a solid).

As we have seen above, the entropy change of the ammonia / hydrogen chloride reaction (‘the system’) is –284 J K -1 mol -1.