GATE

Key Points for Suppositories

Smt. Dr. Jayanti Vijaya Ratna

Vijay Ratna

Let us consider that in a system, PV work is the only useful work or external energy. Let us disregard the electric and other forms of energy. Then the heat content or total energy of a system is divided into internal energy and external energy.

1. H = E + PV

Total energy Internal energy External energy

We can also divide the same total energy (free energy) H into isothermally available energy (TS).

2. H = F + TS

Total energy Isothermally available Isothermally unavailable

Vijay Ratna

In electrochemistry the Nernst equation gives the electrode potential (E), relative to the standard electrode potential (E^O) of the electrode couple or equivalently of the half cells of a battery. In physiology the Nernst equation is used for finding the electric potential of a cell membrane w.r.t. one type of ion.

The activities of pure solid or liquid phases are taken as unity. For a solution at RT (25^OC) the following is true :

Vijay Ratna

Ionic equilibria is about the ionising behaviour of acids and bases. The study of this chapter assumes significance in the light of points such as (1) Most drugs are weak acids and bases and their ionising behaviour in aqueous solutions should be understood for formulating them properly (2) absorption of drugs across biological membranes depends on ionisation, which depends on the pH of the surroundings. In this chapter we study how various substances ionise and how it is related to the pH of the medium. We will also learn to calculate the pH of different solutions from their concentrations. This chapter is divided into (1) Basic definitions (2) Acid-base theroies (3) Ionisation of water, acids and bases (4) pH, H₃O+ and pKa

Vijay Ratna

Thermodynamics deals with the flow of energy. It explains the quantitative relationships between different forms of energy as energy changes from one form to another. The study of thermodynamics consists of understanding (1) Basic definitions (2) First Law (3) Second Law (4) Third Law and (5) Free energy functions. “Energy” and its transfer are applicable in determining the fate of simple chemical processes to describing very complex behavior of biological cells.

I. Basic Definitions :

1. System : A “system” is a well defined part of the universe that one is interested in studying.

2. Open System : An open system is one from which energy and matter can be exchanged with the surroundings.

Vijay Ratna

Viscosity is an expression of the resistance to flow of a system under an applied
stress. The more viscous a system, the greater the applied force required to
make it flow at a particular rate.

The unit of viscosity is the poise, defined as the shearing force required to
produce a velocity of one centimeter per sec. between two parallel planes of
liquid each 1 centimeter square in area and separated by a distance of one
centimeter. The Cgs units for the poise are dyne sec cm^-2. The centipoises
are a more convenient unit of viscosity.

Viscosity is a property which characterizes the flow nature of a liquid. Study of
viscosity helps us in a number of situations and helps us in taking decisions.

Vijay Ratna

Compartment Tray Dryer :

1. Rectangular Chamber, whose walls contain a suitable
   heat insulating material.
2. Material kept on Trays.
3. Dryer is loaded, doors are closed and hot air is
   circulated over trays
4. Direction vanes for uniform velocity distribution of
   air on all the trays.
5. Air is recirculated for economic reasons.
6. Dampers, with the help of automatic instruments,
   control the percentage of fresh air introduced and the moist air
   discharged.
7. Wet scrubbers used for recovery of valuable solvents.
8. If different products are to be dried, thorough
   cleaning is necessary.

Problems:

1. Non-Uniform air flow