Calorimetry: Hess's Law

REFERENCE
General Chemistry for Engineering and Science II- pages 79-94

OBJECTIVES
To practice obtaining measurements of calorimetry and to employ the data to demonstrate Hess’s Law of combining reaction enthalpies.

QUESTION
Did your experiment demonstrate Hess’s Law of heat summation?

DISCUSSION
For this experiment we have to know what Calorimetry, exothermic, endothermic, Hess’s Law, and calorimeter are. Calorimetry is the measurement of the quantity of heat exchanged. Exothermic is a chemical reaction where heat is produced, while endothermic is a chemical reaction where heat is absorbed. Hess’s Law is the heat change in a chemical reaction which is the same regardless of the number of states in which the reaction is affected. Lastly a calorimeter is a device for measuring the amount of heat given out or taken in during a chemical reaction.

CHEMICAL EQUATIONS
Hess’s Law: ΔH_N+ ΔH_S= ΔH_R
Change in Temperature: Δt=t_final-t_inital
Mass of a Solution: 2.05g×(1 mole)/40.00g=0.05125 mol NaOH
Percent Error: % error= ((Sum of ΔH_(N ) and ΔH_S )-ΔH_g)/( ΔH_g ) ×100%

PROCEDURE
(See attached.)
CALCULATIONS
(See attached.)

RESULTS

HYPOTHESIS
If the experiment demonstrated Hess’s Law of heat summation then the ΔH_R will be equal to ΔH_N+ ΔH_S.

OBSERVATIONS
In this experiment there were three different phases, phase one was A: Heat of Neutralization ΔH_N, phase two was B: Heat of Solution ΔH_S and phase three was C: Heat of Reaction ΔH_R. Phase one had four steps and it started with 50mL of 1.0 M HCL and 50.0mL of 1.0 M NaOH being measured out and transferred into two different calorimeters. Both of the substances that were placed in the calorimeters had no color. Next from minute 1-4 the temperature of the HCL was ...

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...nt I was able to calculate the value of ΔH_R by using Hess’s Law of ΔH_N+ ΔH_S= ΔH_R.

CONCLUSION
Based on the objectives, the question, and results from the experiment I can say that I accomplished the objectives of this lab. Also I believe that my results justify the position I took on the hypothesis of: If the experiment demonstrated Hess’s Law of heat summation then the ΔH_R will be equal to ΔH_N+ ΔH_S. My data justifies this because I was able to take the information from phases A, B and C to calculate ΔH_R with Hess’s Law. In the end ΔH_R had a value of -19,095.78 cal/mol (ΔH_R). However when Hess’s Law was used ΔH_(R ) equaled ------------21109.72 cal/mol and from there I calculated the percent error and it was 10.55%.I believe that my data supports my hypothesis because I was able to correctly determine the ΔH_R in the experiment by using Hess’s Law.