Calculations of Kinetic and Thermodynamic Parameters for Thiourea Single Crystals

Abstract

Single crystals of Thiourea (NH2CSNH2) were obtained through simple and inexpensive evaporation technique. The Differential Scanning Calorimetric analysis was also used to identify the purity and melting point (Tm) of the grown crystal. Thermo Gravimetric Analysis has proved useful for evaluating kinetic parameters of various reactions of materials and provides valuable quantitative information regarding the stability of materials. Using the basic relations of thermodynamically variables, Entropy ?S, Enthalpy ?H and Gibb’s free energy ?G were calculated using Horowitz-Metzger relation and summarized in present communication.

Introduction

Context and Importance:
With rising demand for organic and semi-organic materials in Non-Linear Optical (NLO) applications, Thiourea (NH?CSNH?) has emerged as a promising organic material due to its stability, mechanical strength, and optical properties. Single crystals of Thiourea were grown using a simple and cost-effective slow evaporation method.

Objective:
To study the thermal behavior, decomposition kinetics, and thermodynamic properties of Thiourea crystals using Thermo-Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC).

Experimental Methods:

• Crystal Growth: Thiourea crystals were grown using the slow evaporation technique.

• DSC Analysis: Revealed a single endothermic peak indicating phase change between 179.74°C and 182.96°C, confirming the crystal's purity.

• TGA Analysis: Conducted to understand decomposition stages and calculate activation energy.

Kinetic and Thermodynamic Calculations:

• The Horowitz-Metzger method was used to determine kinetic and thermodynamic parameters.

• The relation involves plotting:

  log?[1−(1−α)1−n1−n] vs θ (where θ=T−Tm)\log \left[\frac{1 - (1 - \alpha)^{1-n}}{1 - n}\right] \text{ vs } \theta \text{ (where } \theta = T - T_m\text{)}log[1−n1−(1−α)1−n?] vs θ (where θ=T−Tm?)

• Three decomposition stages were identified with n = 1/2 and corresponding Tm values:

  • Stage 1: Tm = 448.15 K

  • Stage 2: Tm = 500 K

  • Stage 3: Tm = 770 K

• From the slope and intercept of the plots, activation energy (E) and frequency factor were calculated.

Results:

These results confirm a stepwise decomposition process and provide insight into the stability and bond structure of Thiourea crystals.

Conclusion

Thiourea (NH2CSNH2) organic single crystals are successfully grown by using relatively simple and inexpensive slow evaporation of aqueous solution technique. This material has good chemical flexibility to provide non linearity of organic material and strong mechanical property of inorganic material. Kinetic parameters like, Entropy ?S, Enthalpy ?H and Gibb’s free Energy ?G are calculated using basic thermodynamically relations.

References

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Copyright

Copyright © 2025 Minal N. Vansia, Kishor C. Poria. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.