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Enthalpy of Displacement

2748 words (11 pages) Essay in Chemistry

29/01/18 Chemistry Reference this

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  • Saran Singh Sound

Aim: To determine the enthalpy change of displacement between zinc powder and copper sulphate

Zn (s) + CuSO4 (aq) Cu (s) + ZnSO4 (aq)

Chemicals –

  • CuSO­­­4 Solution ( concentration = 0.5 mol.dm3 )
  • Zinc (s) Powder

Data Collection –

Table 1: List of apparatus and Least Count and Uncertainties of Measuring Instruments Used

S. No.

Instrument

Unit

Least Count

Uncertainty

1.

Butter Paper

n/a

n/a

n/a

2.

Cardboard Lid

n/a

n/a

n/a

3.

Digital Laboratory Thermometer

Celsius

0.1 ºC

±0.1 ºC

4.

Digital Weighing Balance

Grams

0.001g

±0.001g

5.

Measuring Cylinder

cm3

1cm3

±0.5cm3

6.

Polystyrene Cup

n/a

n/a

n/a

7.

Digital Stopwatch

Seconds

0.01s

±0.01s

Qualitative Data

  • Time
  • Temperature

Table 2.1: Mass of Zinc Powder

 

Mass of Zinc (s) /M/g/±0.001g

Trial 1

0.244g

Trial 2

2.523g

Trial 3

2.416g

Table 2.2 : Collected Data

Time/t/s/±0.01s

Temperature/T/°c/±0.1°c

Trial 1

Trial 2

Trial 3

30.00

28.4

 

28.6

60.00

28.4

 

28.6

90.00

28.4

 

28.6

120.00

28.4

 

28.6

150.00

29.1

 

33.0

180.00

31.2

 

38.4

210.00

32.9

 

41.9

240.00

35.0

 

44.8

270.00

37.5

 

46.3

300.00

40.0

 

47.2

330.00

41.6

 

47.4

360.00

42.5

 

47.1

390.00

42.5

 

46.6

420.00

42.3

 

45.9

450.00

42.1

 

45.4

480.00

41.6

 

45.0

510.00

41.0

 

44.4

540.00

40.5

 

43.4

570.00

40.0

 

42.8

600.00

39.4

 

41.9

630.00

38.7

 

41.0

660.00

38.0

 

40.6

690.00

37.4

 

39.8

720.00

36.6

 

39.2

750.00

36.0

 

38.4

780.00

35.5

 

37.6

810.00

34.7

 

36.8

840.00

34.0

 

36.0

870.00

33.2

 

35.6

900.00

32.6

 

34.6

930.00

   

33.7

960.00

   

32.9

990.00

   

32.1

Qualitative Observation:

  • It was observed that when Zinc (s) powder was added to the CuSO4­ solution it immediately reacted making the solution warmer .The color of the solution at the beginning was greenish in color which then turned colorless after the Zinc (s) powder had reacted. After the reaction was over, it was observed that Copper had precipitated at the bottom of the cup as a result of it being displaced by Zinc (s) powder.

Formulas:

Mass = No. of Moles (aq) x Molar Mass (s)

And

No. of Moles = Concentration x Volume

And

â-²H = Extrapolation Temperature – Initial Temperature

And

Enthalpy Change = Mass x Specific Heat Capacity x â-²H

And

Molar Enthalpy Change =

And

Mass of water = volume of copper sulphate solution

And

Percentage Deviation = x100

Trial 1:

Volume of CuSO4 (aq)

60.0cm3

Mass of Water

60g

Specific Heat Capacity

4.18 J.g1.ºC-1

Initial Temperature

28.4 ºC

Extrapolation temperature

53.0 ºC

Time at which Zinc (s) powder was added

120s

The graph is used to estimate the change in temperature of the displacement reaction between CuSO4 solution and Zinc (s) powder. The gradient of the best fit line shows the rate of decrease of temperature.

Calculation:-

No. of Moles of 60.0cm3 CuSO4 (aq) = (60/1000) x 0.5 = 0.03 mol

... Mass of Zinc (s) powder = 0.03 x 65 = 1.961g

However for this experiment, mass of zinc had to be taken in excess. Therefore, Mass of Zinc is greater than actual mass required as seen in Table 2.1

â-²H = 28.4 – 53.0 = -24.60 ºC ±0.01s

Enthalpy Change = 60 x 4.18 x -24.6 = -6169.68 J = -6.16968 kJ

Molar Enthalpy Change = = -205.7 kJ.mol-1

As this reaction is exothermic i.e heat is released, enthalpy change is negative.

The literature value of Enthalpy Change for this displacement reaction is -217kJ.mol-1

Percentage Deviation = x 100 = 5.2% Deviation.

Note: There were two assumptions made during this experiment.

  1. The Specific Heat Cpacity of the solution is same as water
  2. No Heat is lost to the surrounding

Trial 2:

Volume of CuSO4 (aq)

70.0cm3

Mass of Water

60g

Specific Heat Capacity

4.18 J.g1.ºC-1

Initial Temperature

28.6ºC

Extrapolation temperature

57.0 ºC

Time at which Zinc (s) powder was added

 

The graph is used to estimate the change in temperature of the displacement reaction between CuSO4 solution and Zinc (s) powder. The gradient of the best fit line shows the rate of decrease of temperature.

Calculation:-

No. of Moles of 70.0cm3 CuSO4 (aq) = (70/1000) x 0.5 = 0.035 mol

... Mass of Zinc (s) powder = 0.035 x 65 = 2.275g

However for this experiment, mass of zinc had to be taken in excess. Therefore, Mass of Zinc is greater than actual mass required as seen in Table 2.1

â-²H = 28.6 – 57.0 = -28.40 ºC ±0.01s

Enthalpy Change = 70 x 4.18 x -28.40 = -8309.84 J = -8.30984 kJ

Molar Enthalpy Change = = -207.7 kJ.mol-1

As this reaction is exothermic i.e heat is released, enthalpy change is negative.

The literature value of Enthalpy Change for this displacement reaction is -217kJ.mol-1

Percentage Deviation = x 100 = 4.3% Deviation.

Note: There were two assumptions made during this experiment.

  1. The Specific Heat Cpacity of the solution is same as water
  2. No Heat is lost to the surrounding

Trial 3:

Volume of CuSO4 (aq)

70.0cm3

Mass of Water

60g

Specific Heat Capacity

4.18 J.g1.ºC-1

Initial Temperature

28.6ºC

Extrapolation temperature

57.0 ºC

Time at which Zinc (s) powder was added

120s

The graph is used to estimate the change in temperature of the displacement reaction between CuSO4 solution and Zinc (s) powder. The gradient of the best fit line shows the rate of decrease of temperature.

Calculation:-

No. of Moles of 70.0cm3 CuSO4 (aq) = (70/1000) x 0.5 = 0.035 mol

... Mass of Zinc (s) powder = 0.035 x 65 = 2.275g

However for this experiment, mass of zinc had to be taken in excess. Therefore, Mass of Zinc is greater than actual mass required as seen in Table 2.1

â-²H = 28.6 – 57.0 = -28.40 ºC ±0.01s

Enthalpy Change = 70 x 4.18 x -28.40 = -8309.84 J = -8.30984 kJ

Molar Enthalpy Change = = -207.7 kJ.mol-1

As this reaction is exothermic i.e heat is released, enthalpy change is negative.

The literature value of Enthalpy Change for this displacement reaction is -217kJ.mol-1

Percentage Deviation = x 100 = 4.3% Deviation.

Note: There were two assumptions made during this experiment.

  1. The Specific Heat Cpacity of the solution is same as water
  2. No Heat is lost to the surrounding

Conclusion:

The displacement reaction between Zinc (s) powder and CuSO4 solution is exothermic as heat is released to its immiediate surroundings. This is supported by the calculations of all the three trials. The Zinc (s) is in powder form which reacts faster with CuSO4 solution as it has a larger surface area. By observing the graph it is found that after reaching the peak temperature, the new solutions temperature starts to decrease which means that its is loosing heat to its surrounding. The line of best fit on the graph shows the temperature change in an ideal situation. However, in reality heat is lost to the surroundings and the specific heat capacity of the solution may not be the same as water. This reaction between Zinc (s) powder and CuSO4­ takes place becaude Zinc (S) powder is more reactive thancopper in CuSO4 solution. Therefore, causing copper to precipitate.

It is also possible that the concentration of the Cuso4 solution was lower , causing less energy to be released then expected.

The temperature change increases as volume of CuSO4 is increased as more Zinc (s) powder is required to react therefore releasing more energy. This is suggested by the calculations for Trial 1, Trial2 and Trial 3.

The percentage deviation of the experimental readings to the literature value is not that high suggesting few errors in the experiment. However, we attributed them to certain and possible errors.

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