A pharmaceutical compound exists in two solid states: a completely crystalline form…
CHEMISTRY · Multi-part · ISC · Chemistry · Chemical Thermodynamics · Types of enthalpy
Problem
A pharmaceutical compound exists in two solid states: a completely crystalline form and a completely amorphous form. The enthalpy of fusion for the crystalline form, measured by differential scanning calorimetry (DSC), is 120Jg−1. A 25.0 g batch of the compound is produced in a pilot plant; DSC analysis of this batch shows an enthalpy of fusion of 70Jg−1 and a broad glass-transition step at 65 °C before melting begins.
Answer the following.
(a) Calculate the mass percent of the batch that is crystalline. Show all work and clearly indicate the units of your final answer.
(b) Classify the overall solid obtained from the pilot plant as purely crystalline, purely amorphous, or a mixed solid. Justify your classification using the numerical result from part (a) and the DSC observations.
(c) The amorphous portion of the drug is more chemically reactive with moisture in air. Predict whether the batch you analyzed will have a longer or shorter shelf life than a 100 % crystalline batch, and explain your reasoning.