Chemical Reaction Lab

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

Dana Lucas
Robin Brown
TA: Chris
February 19, 2018


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
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A stock solution of 6M HCl was added to deionized water in a graduated cylinder in order to dilute it down to 2MHCl. 2MNaOH was added to deionized water to be utilized later. An exothermic reaction occurred due to the fact that diluting the solutions produced heat. LabQuest was used to record data and to put it on a graph. The duration was set to 180 seconds, and the rate was at 15 seconds/sample.
Part B of the experiment was performed in a coffee cup calorimeter that was cleaned between each reaction. 50mL of 2MHCl was measured using a graduated cylinder that got poured into the cylinder in one swift motion. The probe was inserted through the lid, and was made sure that it wasn’t touching the bottom of the cups. LabQuest was run for 3-4 readings, before the NaOH was poured in one motion into the calorimeter, with a stir bar mixing the solutions. The data ran for approximately 3 minutes. Afterwards, the solutions were disposed of in the waste bucket, and were washed
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50mL NaOH was added to the calorimeter where it was then covered with a lid and the probe was inserted. 3-4 readings were obtained and then 50mL NH4Cl was added and stirred with a stir bar. Results were recorded for 3 minutes. Solutions were appropriately disposed of and the equipment was well washed before used again.
Reaction 3 was also similar to reactions 1 and 2. 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

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