Chemical Reaction Lab Report

Introduction, aim and hypothesis
Chemical reactions are accompanied by the release or absorption of energy. Reactions which release energy are described as exothermic and those which absorb energy are endothermic. The energy released in chemical reactions was previously stored as chemical potential energy in the reactants; this stored energy is called enthalpy.
The aim of this practical is to observe and classify chemical processes as endothermic or exothermic, based on the changes in temperature measured and the observations made.
If a chemical reaction produces products with more chemical potential energy than the reactants, then the reaction is endothermic; if the chemical potential energy present after the reaction occurs is lower than the chemical potential energy
that was present in the reactants, then the reaction is endothermic. This change in chemical potential energy will be observed and measured based on the change in temperature of the reaction. Due to my lack of prior knowledge in this situation, I cannot form a more specific hypothesis as to which reactants with behave in what way.
The tasks
A. Solution Processes
B. Ammonium Chloride and Barium Hydroxide
C. Iron and Copper(II) Sulfate
Part A Solution Processes
Equipment (As given in STAWA Exploring Chemistry Year 11; Organic Chemistry; Investigation 35 [page 86])
Procedures (In book)
Results (Temperatures)
Solute
Initial Temp.
(°C)
Final Temp. (°C)
Endothermic/ Exothermic
Sodium Hydroxide NaOH
16.5
19.8
Exothermic
Ammonium Chloride NH4Cl

15.5
Endothermic
Sodium Acetate NaCH3COO

16.2
Slightly endothermic
Sodium Chloride NaCl

16.5
Neither

Part B Ammonium Chloride and Barium Hydroxide
Equipment and procedures (In book)
Results (observations)
A white solid forms in the bottom of the test tube after vigorous shaking; the lowest temperature recorded was 9°C.
Part C Iron and Copper(II) Sulfate
Equipment and procedures (In book)
Results (observations)
The blue solution becomes clear and the steel wool gradually turns red. The wool also heats up to a maximum of 35°C.
Processing the data
Equations
NaOH(s) + H2O(l) → Na+(aq) + OH-(aq) + H2O(l) + ENERGY
NaOH(s) → Na+(aq) + OH-(aq) + ENERGY
NH4Cl(s) + H2O(l) + ENERGY → NH4+(aq) + OH-(aq) + H+(aq) + Cl- (aq)
NH4Cl(s) + H2O(l) + ENERGY → NH4OH(aq) + H+(aq) + Cl- (aq)
NaCH3COO(s) + H2O(l) ENERGY (Small amount) → Na+(aq) + CH3COO-(aq) H2O(l)
NaCH3COO(s) → Na+(aq) + CH3COO-(aq)
No reaction for NaCl and water so no equation
2NaCl(s) + Ba(OH)2(s) → BaCl2(aq) + 2NaOH(aq)
2Fe(s) + CuSO4(aq) → Cu2+(s) + Fe2SO4(aq)
Conclusion (Research all references in
bibliography)
The hypothesis was proven. Exothermic and endothermic reactions are the release and absorption of energy respectively. Exothermic reactions occur when there is chemical potential energy lost in the form of kinetic (heat) energy. These systems have a negative enthalpy because they release energy to the surroundings, resulting in the products having a higher temperature than that of the reactants. Conversely, if more energy is gained than lost, then the reaction is endothermic. The excess energy must have been gained from the surroundings, thus resulting in the temperature dropping.
Sodium hydroxide, ammonium chloride, sodium chloride, ammonium chloride with barium hydroxide, and iron with copper(II) sulfate reacted as expected, however sodium acetate did not.
Heat packs contain NaCH3COO and H2O. NaCH3COO is good at supercooling; it freezes at 54˚C, but it is happy to exist as a liquid at a much lower temperature and is extremely stable. Clicking the button has the ability to force a few molecules to the solid state causing the rest of the liquid then rushes to solidify as well. The temperature of the solidifying liquid jumps up to 54˚C in the process, thus making it an exothermic reaction, not endothermic as observed.
Evaluation
The experiment was valid, as variables like the temperature of the water were relatively constant. The experiment did not contain replicated trials though; a larger sample size of 3 or 5 within the experiment would have helped to obtain results that were not affected by human error, from which an average could have been calculated. However, time restrictions and the amount of chemicals prevented from these ideal situations from occurring.
Preciseness was also a large issue during the experiment because the thermometer had an accuracy of ±0.5˚C. It was not possible to classify all the results obtained, some of the reactions (like that for sodium chloride) could not be easily classified because there was no or very slight difference in temperature. To fix this, more precise equipment should be used next time.
Bibliography (created with CiteThisForMe.com; Harvard Style)
Clarke, J., Baddock, M., Winning, B., Hunneybun, B., Gianatti, S. and Paioff, F. (2014).Exploring Chemistry Year 11 Experiment, Investigations & Problems. Western Australia: STAWA, pp.110, 111.
Deretic, G. (2002). Chemistry practical manual preliminary and HSC. Port Melbourne, Vic.: Heinemann.
Lewis, C. and Lewis, P. (2011). Chemistry for W.A. 1. Australia: Pearson Heinemann, pp.387-399.
800mainstreet.com. Exothermic and Endothermic Reactions, Calculating Energy Changes. [online] Available at: http://www.800mainstreet.com/7/0007-002-exo_endothermic.html [Accessed 28 Jul. 2015].
Chem.ox.ac.uk. Introduction, page 1. [online] Available at: http://www.chem.ox.ac.uk/vrchemistry/energy/default.htm [Accessed 29 Jul. 2015].
Chem.umn.edu. Endothermic and Exothermic Reactions. [online] Available at: http://www.chem.umn.edu/outreach/EndoExo.html [Accessed 27 Jul. 2015].
Chemical Forums. NaOH + H2O reaction. [online] Available at: http://www.chemicalforums.com/index.php?topic=18309.0 [Accessed 28 Jul. 2015].
Chemistry.tutorvista.com. Endothermic Reactions, Examples of Endothermic Reactions | [e-mail]. [online] Available at: http://chemistry.tutorvista.com/physical-chemistry/endothermic-reaction.html [Accessed 27 Jul. 2015].
Chemwiki.ucdavis.edu. Exothermic vs. Endothermic and K - Chemwiki. [online] Available at: http://chemwiki.ucdavis.edu/Physical_Chemistry/Equilibria/Le_Chatelier 's_Principle/Effect_Of_Temperature_On_Equilibrium_Composition/Exothermic_Versus_Endothermic_And_K [Accessed 31 Jul. 2015]. prezi.com. Endothermic and Exothermic Chemical Reactions. [online] Available at: https://prezi.com/ammyhrrewsri/endothermic-and-exothermic-chemical-reactions/ [Accessed 28 Jul. 2015].
Science.uwaterloo.ca. Chemical Reaction Equations. [online] Available at: http://www.science.uwaterloo.ca/~cchieh/cact/c120/reaction.html [Accessed 30 Jul. 2015].