1. BY MARCIA SRI PURWANTININGSIH

2. Hess Law Aim Observe the enthalpy of reaction between NaOH solid and HCl solution with two ways. APPRATUS /CHEMICALS Apparatus: Beaker Glass 250 mL Thermometer Materials: NaOH solid Hydrochloric acid 1 M NaOH Solution 1 M Hydrochloric acid 0.5 M

5. Experiment 1 NaOH (s) + H 2 O (l) NaOH (aq) 2 g 50 cm 3 T water = 26 o C T end = 33 o C

6. Experiment 2 NaOH (aq) + HCl (aq) NaCl (aq) + H 2 O (l) 50 cm 3 1M 50 cm 3 0,5M 50 cm 3 1M 100 cm 3 0,5M T NaOH = 27 o C T HCl = 27 o C T initial = 27 o C T end = 29 o C T end = 30 o C

7. NaOH (S) + HCl (aq) NaCl (aq) + H 2 O (l) 2 g 100 cm 3 0,5M T HCl = 27 o C T end = 38 o C

8. Experiment 1 Q = m. c. t = 50 g. 4,2 j.g -1. o C -1. 7 o C = 1442 joule Mole NaOH = 2/ 40 = 0,05 H 1 per mole = -28840 j = -28,84 kJ

9. Experiment 2 Q = m. c. t = 100 g. 4,2 j.g -1. o C -1. 2 o C = 840 joule Mole NaOH = 2/ 40 = 0,05 Mole HCl = 50 ml. 0,5 M = 0,025 H 2 per mole = -33600 j = -33,600 kJ

10. The other experiment Experiment 2 Q = m. c. t = 150 g. 4,2 j.g -1. o C -1. 3 o C = 1890 joule Mole NaOH = 2/ 40 = 0,05 Mole HCl = 50 ml. 0,5 M = 0,05 H 2 per mole = -37800 j = -37,8 kJ

11. Experiment 3 Q = m. c. t = 100 g. 4,2 j.g -1. o C -1. 9 o C = 3780 joule Mole NaOH = 2/ 40 = 0,05 Mole HCl = 100 ml. 0,5 M = 0,0 5 H 3 per mole = -75600 j = -75,600 kJ

12. Answer of the Question 1. 1. Total equation of the reaction thermochemistry I and II (twice experiment) H 1 + H 2 = -28,84 kJ + (-33,600 kJ) = -62,44 kJ H 1 + H 2 = -28,84 kJ + (-37,8 kJ) = -66,64 kJ 2. Write the equation of the reaction thermochemistry III H 3 = -75,600 kJ 3. Whether the reaction of III equal to the total of reactions I dan II? No, but equal reaction and II less than reaction III

13. 4. According to Hess law : H I + H II = H III Whether your data of experiment appropriate with Hess Law? Yes, although equal H I + H II from my experiment less than asses H III 5. If not, mentioned several factors cause it! Mistake of balance sodium hydroxide solid, because this balance is not stable, mistake of observation, and mistake of measurement.

14. NaOH (S) + H 2 O (l) + 1/2HCl (aq) NaOH (aq) + 1/2HCl (aq) NaCl (aq) + H 2 O (l)

15. Observation Measure ( cylinder, balance) Use balance Inteprating Reading thermometer Accuraty Honesty Responsibility

16. Basic Competence : 2.2. Determining H of reaction based on experiment, Hess law, standard enthalpy change of formation and bond energies data

17. Calculating enthalpy changes of reaction from appropriate experimental results Calculating enthalpy change of reaction using Standard enthalpy change of formation data Calculating enthalpy change of reaction using Cycle diagram and state diagram Calculating enthalpy change of reaction using Bond energy