Firstly, what is thermodynamics? Well it’s
all about heat energy changes and how energy is transferred through chemical systems.
For example, in exothermic reactions the overall potential energy of the
products in less than that of the reactants so more energy is released than is
required to break the necessary bonds. And vice versa for endothermic reactions.
So, let’s look at the fundamental laws of
thermodynamics. The first is one most of us will have heard at some point:
energy cannot be created nor destroyed but merely transferred from one form to
another. The second is that energy will always flow from being concentrated to
being dispersed and that no process can have 100% efficiency for the conversion
of heat energy into “work” which is essentially the energy transfer into our
desired product. This is where it starts to get all confusing, when we consider
entropy. We’ve all seen water evaporate from a pan and seen salt dissolve in
water, both of these happen because particles have a tendency to spread out and
disorder. This disordering or randomness, known as entropy can be calculated using
the entropy change of both the surroundings and the system so that we can
determine whether a reaction is feasible or not feasible. For this we use the
equation: ΔG = ΔH –TΔS where ΔH is the enthalpy change, ΔS in the
entropy change, T is the temperature of the reaction and ΔG is the Gibbs free energy. When ΔG is negative the reaction is said to be feasible and when positive,
not feasible. This feasibility of a reaction is different at different
temperatures. The third law states that as a system approaches 0K the entropy
change also approaches 0JK-1, theoretically though because reaching
0K is impossible. This happens only in
perfect crystals because in non-pure ones energy is required for the imperfect alignment
of the bonds within the crystal.
Author: Grace Ronnie
