Entropy And Enthalpy
Juliet Q Dalagan, PhD
Department of Chemistry
Xavier University-Ateneo de Cagayan
Corrales Avenue, Cagayan de Oro, Philippines
Djamal Nour M. Marohombsar
Roxcil S. Malaque
LeanaDanica S. Orcullo
BSFT - 3 Chem 68 AGA
The experimenters in this experimented using a simple set-up with a testube, heater and a suspended thermometer, monitored the temperature and time during the phase change of a heated sample of naphthalene pellets until melted to freezing point. The time and temperature change of the reaction are graphed to identify the changes in enthalpy and entropy that took place as the melted substance solidifies. Using the data we can then predict the change in free energy, ΔG .
Keywords/s: Entropy, Enthalpy, Free energy, naphthalene
Enthalpy, H, is a thermodynamic property of a system. It is defined as the sum of internal energy U of a system and the product of the pressure and volume of the system: H = U+PV
The PV term represents the mechanical work done on or by the system. Since we are usually more interested in changes than in absolute values, we could write ΔH = ΔU+PΔV
Entropy, S, is an another thermodynamic property., which we can consider as a measure of the disorder or randomness of a system. An ordered system has low entropy. A disordered system has high entropy ΔS equals the heat transferred between the system and its surroundings divided by T: ΔS = Q/T = ΔH/T
Enthalpy and entropy are different quantities. Entropy has the units of heat, joules. Entropy has the units of heat divided by temperature, joules per kelvin. In this experiment, the group would like to compare the entropy, ΔS and enthalpy, ΔH by monitoring the temperature & time during phase change of a melted naphthalene to freezing point. And using the data to predict ΔG. III. Experimental Section
Prepare 250 ml of half full tap water in a beaker to be placed in a ring stand, light the Bunsen burner to begin...
References: Carmichael, L.N., Haines
D.F., and Smoot, R.C. Laboratory Chemistry. Merrill Publishing Co. 1983.
(2014). What is the difference between entropy and enthalpy?. Retrieved from http://socratic.org/questions/what-is-the-difference-between-entropy-and-enthalpy
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