Question

1. what are some examples where thermodynamics (eg. 1st and 2nd law of thermodynamics,enthalpy and entropy,chemical reaction equilibrium) is involved in certain processes in a chemical/pharmaceutical plant?

2. what role does thermodynamics play in a chemical/pharmaceutical plant?

Answer 1

pharmaceutics can use thermodynamic concepts to explain the various phenomena in these fields of study.

For example

The diffusion of the drug through a biological membrane is a spontaneous process

spontaneous implies that the process is natural and irreversible.

When drug molecules move from an area of high drug concentration to an area with low drug concentration, this pathway is spontaneous. It occurs because all natural systems change in such a way so that further changes are less possible or not possible at all ( they approach a state of equilibrium).

These principles can explain the direction of the process, and often they are more applicable nearby an equilibrium point instead of being far away from it. Also, they are more pertinent to isolated closed systems than those encountered in physiological processes.

So the dilemma that faces a pharmacy educator is that how to bring these principles into actual practice. It is perhaps best to explain to students about what the various thermodynamic measures mean rather than how to calculate them from observed data.

For example

The enthalpy, as a thermodynamic measure, is defined by the amount of heat absorbed or released by a system while the system undergoes a change . This is useful to a student-pharmacist who wants to understand how drug molecules dissolve in a solvent system. During dissolution, the system initially absorbs heat from the environment to break down molecular drug aggregates and in the final step the drug molecules thus released can be deposited in the free cavitation available in the solvent. During that deposition of drug molecules in the cavity of the solvent, the system gives up the heat.

Another important measure in thermodynamics is the entropy. It is the thermodynamic measure for the amount of energy that is not useful to do work. The higher the entropy of a system, the closer that system to its point of equilibrium and the lower its capacity to do work

The pharmacy educator may use for example the states of matter to illustrate the concept of entropy to his students. In this case, a crystalline solid has the lowest entropy, followed by the liquid solute, and then the gaseous/vapor phase of the solute where the entropy value is found at its highest.

Another illustration for a thermodynamic measure is the concept of free energy. Generally speaking, the free energy of a system is the amount of energy available to a system to perform work. This often is accompanied initially by the system absorbing heat from the environment. Since the free energy is being utilized by the system to do work, it is expected therefore that it decreases in value as the system is doing work. Thus, the difference in free energy must be negative if the system undergoes a spontaneous reaction. If the change in free energy is positive, then no spontaneous response can happen.

Another pharmaceutical application of the free energy is in the interfacial phenomenon. The ability of one liquid to spread on the surface of another liquid, when this occurs, an amount of free energy is utilized by the system for the spreading to occur. This energy loss by the system is quantified by the difference between the work of adhesion between the two liquids, and the work of cohesion of the fluid which is spreading onto the surface. By convention, when the work of adhesion is greater in value than the work of cohesion, spreading is possible.