Regan Harlacker
Date: 3/28/17
Chemistry-NLC
Calculating Enthalpy
Blake and Jude
Introduction
Enthalpy is a thermodynamic quantity that represents the total heat content of a chemical system. It is the sum of internal energy and the product of the pressure and volume of a thermodynamic system. Enthalpy is generally abbreviated with an “H”. It has the dimensions of energy which is in Joules. The change in enthalpy is formulated as ?T. The enthalpy can’t be measured directly. When a physical or chemical reaction occurs, the enthalpy changes and then it can be measured. For an endothermic reaction, ?H is positive. For an exothermic reaction, ?His negative.
The change in enthalpy is represented by ?H. ?H is the energy change that accompanies a chemical or physical change. An exothermic reaction converts potential energy into kinetic energy. The potential energy after the reaction is less than before the reaction. The ?H of an exothermic reaction is negative. For endothermic reactions, the total potential energy is greater than the potential energy before the reaction. The ?H of an endothermic reaction is positive.

In this experiment, the enthalpy will be determined. The equation used to solve the enthalpy is: -qtotalmNaOH. A chemical reaction will be used: NaOH(s)+HC2H3O2(aq)?H2O(l)+NaC2H3O2(aq). The experiment will be measured using the calorimeter to find heat gain or loss.

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Hypothesis
The chemical reaction will be exothermic because the heat will rise on the thermometer in the calorimeter. This shows that heat was lost.
Materials
A calorimeter
Sodium hydroxide (lye)
Wax paper
A mass scale
Vinegar
Safety goggles
Method
Turn on the mass scale and tare it to zero.

Place the calorimeter onto the scale. Weigh it and record.

Tare the scale so it reads zero.

Add vinegar to the calorimeter until the scale reads anywhere between 115.0 to 125.0g. Record.

Put the lid and thermometer on the calorimeter. Let it sit for a few minutes.

Cut the wax paper into a square. Fold it in half so it creases. Place it on the scale.

Add sodium hydroxide to the paper until the scale reads anywhere between 2.5 and 3g.

Record the temperature of the vinegar.
Stir the mixture with the thermometer.

Clean up the lab.

Results
Table 1: Results of Calculations
Vinegar Calorimeter NaOHQ5200 J 29 J N/A
m116.0g 34.7g 2.5g
c4.1 J/g?1.3 J/g?N/A
?T11?11?N/A
Tf29?29?N/A
Ti18?18?N/A

Calculations
These equations will be used to solve for enthalpy: q=mc?T, ?H=-qtotalmol NaOH, qtotal=q1+q2+…qvinegar=116.0g4.1Jg?11?=5231.6=5200Jqcalorimeter=2.6Jg?11?=28.6=29JHeat capacity of calorimeter= 1.3Jg?2.0g=2.6J?total heat=5200J+29J=5229J2.5g NaOH1×1 mol NaOH40.00gNaOH=0.0625=0.063mol NaOH?H=-5229 J0.063 mol NaOH=-8,300 JmolDiscussion
The hypothesis is correct. The change in enthalpy is negative. The ?H of an exothermic reaction is negative. The hypothesis stated that the reaction was exothermic. This proves that the hypothesis is correct. The change in enthalpy is -8,300 Jmol.
There was one source of error in this experiment. The cups of the calorimeter were made of styrofoam. This method is not the most accurate example of a calorimeter.

Further experimentation could have been done to replace lye with baking soda. References
Dr. Jay L. Wile, Discovering Design with Chemistry, (Muncie, IN: Berean Builders, 2015), p. 417-420
“Bond enthalpy and enthalpy of reaction”, last modified March 20, 2018,
https://www.khanacademy.org/science/chemistry/ap-chemistry/thermodynamics-ap/enthalpy-tutorial-ap/a/bond-enthalpy-and-enthalpy-of-reaction