Enthalpy Of Chemical Reactions Using Hess Law

CH 204- Intro to Chem Practice
Experiment 3-Enthalpy of Chemical Reaction

Dana Lucas
Robin Brown
TA: Chris
February 19, 2018

Introduction

The purpose of this experiment was to calculate the change in enthalpy of 2 reactions using Hess’ Law by using a coffee calorimeter to measure the temperature changes in the sub reactions for MgO and a neutralization reaction.
Germain Hess published this law in 1840, which described the first law of thermodynamics. In Hess’ Law, “the enthalpy change in a chemical reaction is independent of any intermediate reactions; that is, it is the same whether it takes place in one or several stages”1.
The change in enthalpy can be described by the equation:

The enthalpy, or heat, of reaction is described as products

50mL HCl was added to the calorimeter, which was covered with the lid and inserted with a probe. Readings were collected and then 50mL NH4OH was swiftly added to the solution, with the stir bar mixing the reaction constantly. The initial and max temperature temperatures were recorded and the change in temperature was recorded. The data was saved onto the USB.
Regarding reaction 4, the duration was changed to 480 seconds. After the Styrofoam cups were restacked, 100mL HCl was added. The lid was added and the probe was instered. A watch glass was weighed, then weighed again after scooping on 1.0g MgO. After 3-4 readings were recorded, the MgO was added with the spatula, which was stirred constantly with the stir bar. The watch glass was weighed again with the remains of the MgO.
Reaction 5 did not use the stock solution. It required the diluted 2MHCl. 120mL of this HCl was added to the calorimeter, which got covered by the lid and the probe was inserted. A watch glass was weighed again, first without MgO, then with 1.0g MgO. After 3-4 readings were collected, the MgO was added and stirred constantly. The watch glass was weighed then again. Weight measurements were recorded. The data was then saved onto the