THE REPORT RESULT OF EXPERIMENT HESS

LAWBY

MARCIA SRI PURWANTININGSIH

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

oProcedures

1. Weigh as soon as possible of NaOH and then store in a closed place.

2. Do the experiment in accordance with the following columns.

OBSERVATIONExperiment 1

NaOH(s) + H2O(l) NaOH (aq)

2 g 50 cm3

Twater = 26 oC

T end = 33 oC

Experiment 2

NaOH(aq) + HCl (aq) NaCl(aq) + H2O(l)

50 cm31M 50 cm3 0,5M

50 cm3 1M 100 cm3 0,5M

TNaOH = 27 oCT HCl = 27oCT initial = 27oCT end = 29oC

T end = 30oC

NaOH(S) + HCl (aq) NaCl(aq) + H2O(l)

2 g 100 cm3 0,5M

T HCl = 27 oC Tend = 38 oC

Experiment 3

Calculation

Experiment 1Q = m . c . t = 50 g . 4,2 j.g-1.oC-1 . 7oC = 1442 jouleMole NaOH = 2/ 40 = 0,05H1 per mole

= -28840 j= -28,84 kJ

Experiment 2Q = m . c . t = 100 g . 4,2 j.g-1.oC-1 . 2oC = 840 jouleMole NaOH = 2/ 40 = 0,05Mole HCl = 50 ml . 0,5 M = 0,025H2 per mole

= -33600 j= -33,600 kJ

The other experimentExperiment 2Q = m . c . t = 150 g . 4,2 j.g-1.oC-1 . 3oC = 1890 jouleMole NaOH = 2/ 40 = 0,05Mole HCl = 50 ml . 0,5 M = 0,05H2 per mole

= -37800 j= -37,8 kJ

Experiment 3Q = m . c . t = 100 g . 4,2 j.g-1.oC-1 . 9oC = 3780 jouleMole NaOH = 2/ 40 = 0,05Mole HCl = 100 ml . 0,5 M = 0,0 5H3 per mole

= -75600 j= -75,600 kJ

Answer of the Question 1. 1. Total equation of the reaction

thermochemistry I and II (twice experiment) H1 + H2 = -28,84 kJ + (-33,600 kJ) = -62,44 kJ H1 + H2 = -28,84 kJ + (-37,8 kJ) = -66,64 kJ 2. Write the equation of the reaction thermochemistry III

H3 = -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

4. According to Hess law : HI + HII = HIII

Whether your data of experiment appropriate with Hess Law? Yes, although equal HI + HII from my experiment less than asses HIII

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.

NaOH(S) + H2O(l) + 1/2HCl (aq)

NaOH(aq) + 1/2HCl (aq)

NaCl(aq) + H2O(l)

6. Make the diagram for the reaction of the experiment!

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

Proses Skill

Basic Competence :2.2. Determining H of reaction based on

experiment, Hess law, standard enthalpy change of formation and bond energies data

Standard of Competence :

2. Understanding the enthalpy changes in chemical reaction and its calculations

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

 

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