Practical Writeup Experiment 2, Thermodynamics of the Rhodamine B Lactone Zwitterion Equilibrium

1937 Words Apr 21st, 2013 8 Pages
AIM:
The aim of the experiment was to determine the enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG) for the Rhodamine β-Lactone Equilibrium. To accomplish this, a manual spectrophotometer was used to determine the maximum absorbance of a sample of Rhodamine β-Lactone. The absorbance of the sample was then measured over a range of temperatures from which the equilibrium constant (K), enthalpy (ΔH), entropy (ΔS) and Gibbs free energy were then calculated.

INTRODUCTION:
The xanthene dye Rhodamine β-Lactone can undergo multiple equilibria. “In protic solutions, Rhodamine β-Lactone exists as an equilibrium mixture of a colourless lactone and a coloured zwitterions.” [1] as shown in appendix 1. The position of the equilibrium
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a sample of Rhodamine β-Lactone across a range of wavelengths (450nm-650nm) using a UV/Vis spectrophotometer

Temp (°C) | Temp (°K) | 1/T (K-1) | Abs (AT) | Density (ρT) (gcm-3) | Zwitterion Concentration [Z] | Lactone Concentration [L] | Equilibrium Constant (K) | lnK | Gibbs Free Energy (ΔG) | 10 | 283.15 | 0.003532 | 0.62 | 0.811693 | 0.593106 | 0.406894 | 1.457642 | 0.37682 | -887.075 | 15 | 288.15 | 0.00347 | 0.6 | 0.807543 | 0.576923 | 0.423077 | 1.363636 | 0.310155 | -743.032 | 20 | 293.15 | 0.003411 | 0.6 | 0.803393 | 0.579903 | 0.420097 | 1.380404 | 0.322376 | -785.711 | 25 | 298.15 | 0.003354 | 0.59 | 0.799243 | 0.573199 | 0.426801 | 1.343013 | 0.294915 | -731.042 | 30 | 303.15 | 0.003299 | 0.58 | 0.795093 | 0.566425 | 0.433575 | 1.306406 | 0.26728 | -673.649 | 35 | 308.15 | 0.003245 | 0.52 | 0.790943 | 0.510494 | 0.489506 | 1.042875 | 0.041981 | -107.555 | 40 | 313.15 | 0.003193 | 0.5 | 0.786793 | 0.493449 | 0.506551 | 0.974133 | -0.02621 | 68.23197 | 45 | 318.15 | 0.003143 | 0.47 | 0.782643 | 0.466301 | 0.533699 | 0.873716 | -0.135 | 357.0887 | 50 | 323.15 | 0.003095 | 0.45 | 0.778493 | 0.448839 | 0.551161 | 0.81435 | -0.20536 | 551.7469 | 55 | 328.15 | 0.003047 | 0.42 | 0.774343 | 0.421161 | 0.578839 | 0.727596 | -0.31801 | 867.6042 | 60 | 333.15 | 0.003002 | 0.38 | 0.770193 | 0.383104 | 0.616896 | 0.621018 | -0.4764 | 1319.524 | 23.4 | 296.55 | 0.003372 | 0.6 | 0.800571 | 0.581947 | 0.418053 | 1.392043 | 0.330773 | -815.526 |

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