Enthalpy of Reaction and Hess’s Law Essay

I. PurposeThe purpose of this lab is to allege Hesss Law through the troika replys of NaOH and HCl, NH4Cl and NaOH, and NH3 and HCl. The union of the enthalpies of the first two receptions should lucifer the henry of the triad reception.II. BackgroundHesss Law is employ to determine the enthalpy of a reception from adding two or more preceding reactions. To determine the enthalpies of trustworthy chemical reactions, the change in essential be measured. This is opera hat done employ a calorimeter to prevent combust dismissal to the surroundings. To calculate the ignite change in issue, the q=mct comparability must be used. A positive value for q elbow room the solution gains fondness, a invalidating value means the solution loses heat and is exothermic. The reactions used in the lab be exothermic acid-base neutralizations. By calculating q, heat, the enthalpy of reaction endure be found by conditioned the Molarity of the reactants. The specific heat of the c alorimeter fecal matter be found by the comparison qcal= t x heat capacity. Since a calorimeter is used the heat released from the reaction lead be absorbed in the solution, sequence some heat is transferred to the calorimeter. So the q of the reaction is given by this equation qrxn= (qsol+qcal).III. epitome of ProcedurePart 1A calorimeter is to be arranged victimisation Styrofoam cupfuls and a hole on top of a tiptop to take the temperature while as well as preventing heat loss. 50mls of distilled is to be added to the calorimeter. 75mls must so be heated to 70 degrees Celsius and 50mls of that piddle is to be added to the calorimeter. The calorimeter has to be covered and whence the temperature taken every 20 seconds for 3 minutes.Part 250mls of 2.0M HCl must be put into the calorimeter. A 50mls solution of 2.0M NaOH should then be added to the HCl solution and stirred. The temperature needs to be recorded every 20 seconds for 3 minutes. For the second reaction the s ame do work has to be repeated using 2.0M NH4Cl and 2.0M NaOH. The triplet reaction requires the same process using 2.0M solutions of NH3 and HCl.IV. Observations* Styrofoam cup becoming hot afterward mixture* thermometer scraping the Styrofoam cup sides* cover doesnt completely cover the cup* pocket-size amount of time amid pouring the chemicals and covering and mixingVI. Results and QuestionsCalculations amuse see attached graphs and work.Post research lab Questions1. What is meant by calorimetry?Calorimetry is the scientific measuring of heat released during chemical and physical changes. It ensures that minimal heat is befogged so the heat of reaction can be found accurately.2. How does lifelike analysis improve the accuracy of the selective in fundamental law?Once the points are plotted on a graph the bank bill of best fit can be cadaverous and extrapolated toward the y-axis. Since the first data plots can be inconsistent the best fit line may ignore the first point s reservation the data more accurate by disregarding the inaccurate data.3. What is the meaning of the negative home in front of the equation for heat of reaction?The negative sign in front of the brackets indicate that we are in fact solving for the atavism reaction. So the sign must sire a negative to indicate the reaction that is the forward, exothermic, reaction.4. Do the lab results support Hesss Law?The lab does support Hesss Law. The percent error is relatively small for this lab and algebraically it is proven that the sum of the enthalpies of the first two reactions is close the measured value of the third reaction.5. How could the procedure be modified to achieve greater accuracy?To improve the accuracy of the lab a formal capacitor could be used instead of average Styrofoam cups. An airtight revenue stampskin between the cover and thermometer would also be more accurate by preventing heat loss to the surroundings.6. Find a set back reference that lists standard heat of formation for the species included in your net loft equations. Use them to calculate delta H for the reaction of the net ionic equations. Do these determine support Hesss Law? gull attached calculations.VII. ConclusionThis lab successfully verified Hesss Law by adding enthalpies of reactions to equal the enthalpy of a third reaction. The mix of NaOH with HCl, and NH4 with NaOH proved to give run into a heat close to that of NH3 compound with HCl. The percent error proved to be 3.72%. The sources of error could be the heat lost while the calorimeter was not covered and perhaps not enough mixing passim the duration of the three minutes. The addition of a mixing unit and an airtight seal on the capacitors would provide an improved discrepancy of this lab.