Enthalpy of Reaction and Hess’s Law Essay

I. PurposeThe purpose of this lab is to put forward Hesss Law through the triple replys of NaOH and HCl, NH4Cl and NaOH, and NH3 and HCl. The center field of the enthalpies of the first two receptions should extend to the enthalpy of the troika reply.II. BackgroundHesss Law is utilize to determine the enthalpy of a reaction from adding two or more preceding reactions. To determine the enthalpies of certain(a) chemical reactions, the change in moldiness be thrifty. This is exceed done employ a calorimeter to prevent high temperature loss to the surroundings. To calculate the awake change in firmness, the q=mct equating must be used. A positive value for q center the solution gains wake, a interdict value means the solution loses heat and is exothermic. The reactions used in the lab ar exothermic acid-base neutralizations. By calculating q, heat, the enthalpy of reaction kindle be found by intimate the Molarity of the reactants. The specific heat of the calorime ter arsehole be found by the par qcal= t x heat capacity. Since a calorimeter is used the heat released from the reaction get out be absorbed in the solution, turn some heat is transferred to the calorimeter. So the q of the reaction is given by this equation qrxn= (qsol+qcal).III. compendious of ProcedurePart 1A calorimeter is to be arranged employ Styrofoam loving cups and a hole on top of a hide out to take the temperature while besides preventing heat loss. 50mls of distilled is to be added to the calorimeter. 75mls must and so be heated to 70 degrees Celsius and 50mls of that pee is to be added to the calorimeter. The calorimeter has to be covered and because 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 hence 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 same bear on has to be repeated using 2.0M NH4Cl and 2.0M NaOH. The trey reaction requires the same process using 2.0M solutions of NH3 and HCl.IV. Observations* Styrofoam cup becoming hot subsequently mixture* thermometer scraping the Styrofoam cup sides* cover doesnt completely cover the cup* atrophied amount of time mingled with pouring the chemicals and covering and mixingVI. Results and QuestionsCalculations enchant see attached graphs and work.Post research laboratory 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 garbled so the heat of reaction can be found accurately.2. How does graphical analysis improve the trueness of the entropy?Once the points are plotted on a graph the draw pip of best fit can be bony and extrapolated toward the y-axis. Since the first data plots can be inconsistent the best fit line may ignore the first points reservation the data more a ccurate by disregarding the inaccurate data.3. What is the meaning of the negative point 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 turnabout reaction. So the sign must go 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 pestle between the cover and thermometer would also be more accurate by preventing heat loss to the surroundings.6. Find a dishearten reference that lists standard heat of physical composition for the speci es included in your net loft equations. Use them to calculate delta H for the reaction of the net ionic equations. Do these set support Hesss Law? confab 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 off a heat close to that of NH3 merge 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 maybe not enough mixing throughout the duration of the three minutes. The addition of a mixing unit and an airtight seal off on the capacitors would provide an improved variant of this lab.