Expt 2-Calorimetry

31
Calorime try Franz Laurence L. Alvarez Louise Gabrielle M. Valdez

description

Chemistry 18.1 - General Chemistry Laboratory II

Transcript of Expt 2-Calorimetry

Page 1: Expt 2-Calorimetry

CalorimetryFranz Laurence L. Alvarez

Louise Gabrielle M. Valdez

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Theoretical Framework Calorimetry

Science of measuring the heats of reaction Calorimetric techniques: based on the

measurement of heat that may be: Generated (exothermic) Consumed (endothermic) Dissipated

In measuring change in enthalpy (∆H): Construct a “surroundings” retains heat, where

temperature change is observed

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Theoretical Framework Calorimeter

Apparatus used to measure heat released or absorbed

Acts as the “surroundings” Changes temperature when heat is transferred to

or from the system

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Calorimeter:

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Theoretical Framework Heat capacity

Quantity of heat required to change an object’s temperature by 1K

Specific heat capacity Quantity of heat required to change the

temperature of 1 gram of a substance by 1K

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Theoretical Framework The heat released (Q) by a reaction is

absorbed by the calorimeter and any substances in the calorimeter.

The following energy balance exists if the only substance in the calorimeter is water:

0 = Qcal + Qwater

Remember: First law of Thermodynamics when energy is transferred from one object to another, it appears as work and/or as heat

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Experimental Part A: Calorimeter Constant

This is the final /equilibrium temperature.

This is the initial temperature of calorimeter and water.

10mL of tap water

Calorimeter with

thermometer

Record temperature

until 3 identical readings

50mL of tap water

Heat to 50oC (use

another

thermometer)

10mL of hot water

Calorimeter with tap water

Record temperature every

3s until temp becomes constant for 4 successive

readings.

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Part B: Heat of Fusion

This is the final /equilibrium temperature.

Determine weight of beaker with tissue and weight of ice.

This is the initial temperature of calorimeter and water.

10mL of tap water

Calorimeter with

thermometer

Record temperature

until 3 identical readings

Weigh 10g of ice in beaker with tissue paper at bottom

Calorimeter with tap water

Record temperature every 3s until temp becomes constant for 4 successive

readings.

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Part C: Heat of Reaction

Place in water bath if temp is not equal

Record temperature of each reagent

Read temperature (initial temp) Measure

volume

Mix reagents in calorimeter

Record temperature every 3s until temp becomes constant

Set I:5.5mL 6M HCl + 4.5mL 6M NaOH

Set II5.5mL 6M HOAc + 4.5mL 6M NaOH

Set III5.5mL 6M HCl + 4.5mL 6M NH4OH

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Results Part A

Mass of tap water: 10g Mass of hot water: 10g Initial temperature of tap water: 35oC Initial temperature of hot water: 50oC Equilibrium temperature: 41oC Calorimeter constant, cal/oC: 5 cal/oC

Time (s) 0 3 6 9 12 15Temperature (oC) 40 41 41 41 41 41

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Part A.Evaluation of Calorimeter Constant

39.8

40

40.2

40.4

40.6

40.8

41

41.2

0 2 4 6 8 10 12 14 16

Time (s)

Tem

per

atu

re (

C)

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Results Part B

Mass of tap water: 10g Mass of ice + beaker +

tissue: 34.45g Mass of beaker + tissue:

24.39g Mass of ice: 10.06g Initial temperature of tap

water: 34oC Initial temperature of ice: 0oC Equilibrium temperature: 7oC Calorimeter constant: 5

cal/oC Heat of fusion of ice, cal/g:

37.74 cal/g

Time (s) Temp (oC)

0 23

3 20

6 17

9 15

12 13

15 12

18 11

21 10

24 10

27 9

30 9

Time (s) Temp (oC)

33 8.5

39 8

42 8

45 7.5

48 7.5

51 7

54 7

55 7

57 7

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Part B.Evaluation of Heat Fusion of Ice

0

5

10

15

20

25

0 10 20 30 40 50 60

Time (s)

Tem

per

atu

re (

C)

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Results Part C.

Set I: 5.5mL 6M HCl + 4.5mL 6M NaOH

Mols of HCl: 0.033 mols

Mols of NaOH: 0.027 mols

Mols of limiting reagent: 0.027 mols

∆H of neutralization: -15.56 x 103 cal/mol

Time (s) Temperature (oC)

0 35

3 45

6 54

9 58

12 60

15 62

18 63

21 63

24 63

27 63

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Part C: Set I

Evaluation of Heat of Reaction of Set I

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30

Time (s)

Tem

per

atu

re (

C)

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Part C. Set II: 5.5mL 6M HOAc

+ 4.5mL 6M NaOH

Mols of HOAc: 0.033 mols

Mols of NaOH: 0.027 mols

Mols of limiting reagent: 0.027 mols

∆H of neutralization: -3.61 x 103 cal/mol

Time (s) Temperature (oC)

0 50

3 55

6 56

9 56.5

12 56.5

15 56.5

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Part C: Set II

Evaluation of Heat of Reaction of Set II

49

50

51

52

53

54

55

56

57

0 2 4 6 8 10 12 14 16

Time (s)

Tem

per

atu

re (

C)

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Part C. Set III: 5.5mL 6M HCl +

4.5mL 6M NH4OH

Mols of HCl: 0.033 mols

Mols of NH4OH: 0.027 mols

Mols of limiting reagent: 0.027 mols

∆H of neutralization: -13.33 x 103 cal/mol

Time (s) Temperature (oC)

0 34

3 43

6 49

9 52

12 55

15 56

18 57

21 57.5

24 58

27 58

30 58

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Evaluation of Heat of Reaction of Set III

0

10

20

30

40

50

60

70

0 5 10 15 20 25 30 35

Time (s)

Tem

per

atu

re (

C)

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Discussion Part A: Calorimeter Constant Qhot water + Qtap water + Qcalorimeter = 0 *Q = m c ∆ t ; Qcalorimeter = ccalorimeter ∆ t Qcal = -mtapc∆ttap – mhotc∆thot

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Part A: Calculations

Qcal = -mtapc∆ttap – mhotc∆thot

= -(10g) (1.00 cal/goC) [(41-35) + (41-50)]oC

= 30 cal

Ccal = Qcal/∆t = 30cal / (41-35)oC = 5 cal/oC

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Discussion

Part B: Heat of Fusion

∆Hfusion = (-Qice – Qtap – Qcal) ÷ mice

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Part B: Calculations

∆Hfusion = -Qice – Qtap – Qcal ÷ mice

= {[-10.06g(4.184J/goC)(7-0)oC] – [10g(4.184J/goC)(7-34)oC] –

[(5cal/oC)(7-34)oC(4.184J/cal)]} ÷ 10.06g

= 139.15 J/g 33.25 cal/g

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Discussion Part C: Heat of Neutralization

∆Hneut = (-Qcal – Qsol’n) ÷ mollimiting

∆ Hneut = (-Ccal∆t – msol’ncsp∆t) ÷ mollimiting

∆ Hneut = [-msol’ncsp(tf - ti) – Ccal (tf - ti)] ÷ mollimiting

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Part C: Set I: Calculations

∆Hneut = (-Qcal – Qsol’n) ÷ mollimiting

∆ Hneut = (-Ccal∆t – msol’ncsp∆t) ÷ mollimiting

∆ Hneut = [-msol’ncsp(tf - ti) – Ccal (tf - ti)] ÷ mollimiting

= [(-10g)(1.00cal/goC)(63-35)oC –

(5cal/ oC)(63-35)oC] ÷ 0.027 mol= -15.56 x 103 cal/mol

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Part C: Set II: Calculations

∆Hneut = (-10g)(1.00cal/goC)(56.5-50)oC –

(5cal/oC)(56.5-50)oC ÷ 0.027 mol

= -3.61 x 103 cal/mol

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Part C: Set III: Calculations

∆Hneut = (-10g)(1.00cal/goC)(58-34)oC –

(5cal/oC)(58-34)oC ÷ 0.027 mol

= -13.33 x 103 cal/mol

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COMPARISON OF VALUES

Experimental Values

∆Hfusion = 139.15 J/g ∆Hneut(SET I) = -15.56 x

103 cal/mol ∆Hneut(SET II) = -3.61 x

103 cal/mol ∆Hneut(SET III) = -13.33 x

103 cal/mol

Theoretical Values 333.55 J/g -13.48 x 103 cal/mol

-13.42 x 103 cal/mol

-11.92 x 103 cal/mol

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Conclusion and Recommendation Calorimetry is very helpful in determining

heats of reaction especially in chemistry experiments. We found out that heat is related with temperature and it can be defined in many ways.

Conservation of energy is also a part of heat processes were heat is neither created or destroyed but instead, it is passed on by the system to the surroundings or vice versa. Conservation of such energy gives definition for endothermic and exothermic reactions.

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Conclusion and Recommendation Calorimeter constant is the specific heat of

the calorimeter. Specific heats of different calorimeters vary from each other.

The heat of fusion is the amount of thermal energy which must be absorbed or evolved for 1 mole of a substance to change states from a solid to a liquid or vice versa. The heat of fusion in the experiment may be positive or negative with respect to different substances. It is endothermic in the experiment with respect to ice.

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Conclusion and Recommendation The heat of neutralization is the

amount of heat involved (either given off or absorbed) in the neutralization reaction of acids and bases to form salt and water.

Different factors affect the experiment that led to different experimental errors and that not all experimental measurements were so accurate.