# Enthalpy Lab Background

Topics: Entropy, Thermodynamics, Temperature Pages: 2 (751 words) Published: November 12, 2012
Enthalpy, represented by the sign ∆H in kJ/mol, is the heat change in a reaction. It shows whether how much heat is released or absorbed during the reaction. If the reaction is endothermic, the enthalpy would be positive and if the reaction is exothermic, the enthalpy would be negative. During a chemical reaction, which consists of breaking and creating bonds, heat is either absorbed or released. In this lab, the reaction uses the disassociation of an ionic compound ammonium nitrate shown in the equation #1 below into ions. In order to disassociate ammonium nitrate into ions, energy is required. Both NH4 and NO3 are always soluble, therefore the ionic compound disassociates completely. Through equation #2, heat absorbed or released can be measured. In equation #2, q stands for the heat change in joules, m for the mass of the water in grams, C for the specific heat of water, and ∆T for the change in temperature. By using the calorimeter with a stir rod, change in temperature is found. 1.NH4NO3(s) NH4(aq) + NO3(aq)

2.q=mC∆T
Free energy is a thermodynamic function that shows the available energy that can be converted into work. By using the Gibbs-Helmholtz equation, which uses free energy and is shown in equation #3, spontaneity of the reaction can be found using enthalpy, temperature, and entropy. Free energy, unlike entropy, is an absolute way to determine whether the reaction is spontaneous or not. If the free energy is negative, then the reaction is spontaneous, whereas if the free reaction is positive, then the reaction is not spontaneous. If free energy is neither, meaning if the free energy is zero, the reaction has reached equilibrium, therefore not shifting to left or right. In this lab, the reaction shown in equation #1 reaches equilibrium, so the free energy of this reaction would be zero.

Entropy, shown by the sign S, is the measurement of molecular randomness or disorder. It is given in J/K*mol and it determines the disorder by the number of...