Show that the two equations for reactions 1 and 3 shown below can be added algebraically to give the equation for reaction 2 in the middle. NaOH(s) Na+(aq) + OH– (aq) Reaction 1 NaOH(s) + H+(aq) + Cl– (aq) H2O(l) + Na+(aq) + Cl– (aq) Reaction 2 Na+(aq) + OH–(aq) + H+(aq) + Cl–(aq) H2O(l) + Na+(aq) + Cl–(aq) Reaction 3
5 2. Applying Hess’s Law and the result from the previous question, calculate the theoretical ΔH for reaction 2 using only the experimental ΔH values for reactions 1 and 3. NaOH(s) Na+(aq) + OH– (aq) ΔHreaction1 NaOH(s) + H+(aq) + Cl– (aq) H2O(l) + Na+(aq) + Cl– (aq) ΔHreaction2 Na+(aq) + OH–(aq) + H+(aq) + Cl–(aq) H2O(l) + Na+(aq) + Cl–(aq) ΔHreaction33. Compare the theoretically calculated enthalpy of reaction, ΔHtheoretical, for reaction 2 (from the previous question) with the experimentally determined enthalpy of reaction, ΔHexperimental, for reaction 2 (from simulation). Calculate the absolute difference between ΔHtheoretical and ΔHexperimental. Show your calculations. 4. If the absolute difference between ΔHtheoretical and ΔHexperimental is equal or less than 10 kJ/mol, then assume that the difference is negligible and that ΔHtheoretical = ΔHexperimental. According to your virtual experimental results, is Hess’s Law valid? Explain.
6 5. In reaction 1, a student measured the temperature of the resultant solution when some NaOH pellets were still left in the calorimeter. How does it affect the value of ΔHreaction1 ? 6. In reaction 2, a student forgot to put the lid back on the calorimeter after mixing NaOH pellet with HCl solution. How does it affect the value of ΔHreaction2 ? 7. In reaction 3, a student left the solution stirring for 30 min while talking to a friend. How does it affect the value of ΔHreaction3 ? 8. In this experiment, we assumed the density of water or any solution is 1.00 g/mL and that the specific heat capacity of any solution is 4.184 J/(g·°C) to simplify the calculation. List another assumption we made in this experiment.
