Thermodynamics with a focus on entropy

There are many factors which will affect whether a reaction will take place spontaneously. For a reaction to occur spontaneously it does not require an external influence such as energy, for it to occur. For example enthalpy change (ΔH, where delta means ‘change in’). Can you think of how this affects the spontaneity of a reaction?·      ΔH – exothermic reactions lead to product(s) which are more stable than the reactants as energy is released. This is a driving force behind many reactions and causes them to be spontaneous. An exothermic reaction has a -ve ΔH.
However, some reactions which are endothermic can occur spontaneously. How is this possible?ENTROPY!
Entropy(S) is a measure of disorder of a system. It describes the number of ways atoms can share quanta of energy. A system is disorder if there are many ways of sharing energy. A more disordered system will have a higher entropy than a less disorder system.
Substances with more ways of arranging their atoms and energy (more disordered) have a higher entropy.Let’s take a look at an example,
·      Solids<liquids<gases. This is because if we consider the atomic structure of these states, a solid has atoms which are very close together and have little movement. It is ordered and has a low S. On the other hand, gases have atoms which move erratically and can share energy in several ways. It is very disordered and has a high S. An increase in disorder and entropy will lead to a positive entropy change ∆S˚ = +ve