The calorimeter above was used to determine the enthalpy of the reaction between

Question

The calorimeter above was used to determine the enthalpy of the reaction between hydrochloric acid and sodium hydroxide. The relevant temperatures at the time of reaction (assuming the reaction was instantaneous) were determined as above. Temperatures were recorded as a function of time and extrapolated to the time of mixing. The generic graph is shown below. The temperature axis is again intentionally not displayed. The relevant information is given in table below. If the temperatures of the acid and base at the time of mixing are different, use their average as the temperature of the mixture before reaction. Use the average also as the initial temperature of the calorimeter. What is the limiting reagent? A. HCl B. NaOH C. The number of moles of acid and base are equal How many moles of the limiting reagent reacted? What si the average temperature of the mixture of HCl and NaOH at 3.00 min (before they have reacted)? What is the weight of the reaction solution in grams? What is the change in temperature experienced by the reaction mixture (and the calorimeter back to the time of mixing? How much of the heat liberated by the reaction (in kJ) went to heating up the reaction solution? What is the enthalpy change (in kJ) for the reaction? (Pay attention to the sign!) This question explores the impact of the calorimeter constant on the final result. What percentage of the total enthalpy of the reaction is observed by the calorimeter? What is the molar enthalpy Delta H_, of the reaction is: H^+(aq) + OH^+(aq) rightarrow H_2O(l) The above experiment is repeated using the network using the weak monoprotic acid, in place of hydrochloric acid. The molar enthalpy of the reaction between the propionic acid and sodium hydroxide, Delta H_weak is determined to be -48.3 kJ/mol. Using Hess' Law and your result for HCl, what is the enthalpy of dissociated of propionic acid in kJ/mol?

Explanation / Answer

HCl + NaOH --> NaCl + H2O

5. moles HCl = 2.42 M x 50 ml = 121 mmol

moles NaOH = 2.21 M x 55 ml = 121.55 mmol

Limiting reactant

A. HCl

6. moles limiting reactant HCl reacted = 121 mmol

7. Average temperature (HCl + NaOH) = 27.6 oC

8. Weight of reaction mixture = (50 + 55) ml x 1.02 g/ml = 107.1 g

9. Change in temperature of mixture = 42.1 - 27.6 = 14.5 oC

10. heat utilized to heat the reaction = 104.75 x 3.97 x 14.5 = 6.030 kJ

11. Heat absorbed by calorimeter = 107.1 x 3.97 x 14.5 - 104.75 x 3.97 x 14.5 = 6.165 - 6.030 = 0.135 kJ

12. Enthalpy change for the reaction = 6.165 kJ

13. % of total enthalpy absprbed by calorimeter = 0.135 x 100/6.165 = 2.20%

14. molar enthalpy of reaction = 6.165/0.121 mol = 50.950 kJ/mol

15. Enthalpy of dissociation of propionic acid = -48.3 - 50.950 = -99.250 kJ/mol

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.