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Enthalpy. This experiment's aim is to find out, enthalpy change of a reaction, and to determine whether it is exothermic or endothermic.

Free essay example:

Lab report on Emthapy

Aim :

This experiment's aim is to find out, enthalpy change of a reaction, and to determine whether it is exothermic or endothermic.

Apparatus :

Measuring Trays                        

Weighing Scale

Citric acid

Sodium Carbonate

Polystyrene cup

Thermometer

Reaction beaker + lid

Copper Sulphate

Zinc (powdered)

Stopwatch

Method:

  1. Pour 25 ml of Copper Sulphate into the reaction beaker.
  2. Place the reaction beaker in the polystyrene cup and put the thermometer in the cap.
  3. Record the temperature of the solution.
  4. Add the 0.5 grams of Zinc powder and close the lid immediately.
  5. Record Maximum change of temperature.
  6. Repeat steps 1 – 5 but this time use citric acid in place of Copper Sulphate and 3 grams of Sodium Carbonate instead of zinc.
  7. Calculate energy change for the amounts of substance used.
  8. Calculate the amount of the reactant in solution in the cup.
  9. For each reaction calculate energy change per mole of the reactant which was in solution at the start.
  10. Write a symbol equation for the first reaction and a word equation for the second one.
  11. Write the energy change per mole of citric acid.
  12.  Draw an energy level diagram for the enthalpy change of both reactions.

Diagram of Apparatus:

Results:

Starting temperature:

Reaction

Product

Trial 1

 Trial 2

Trial 3

Average temperature

1

Zinc Sulphate

23

21

23

5

2

Sodium Citrate

19

20

18

Final temperature:

Reaction

Product

Trial 1

Trial 2

Trial 3

Average temperature

1

Zinc Sulphate

29

25

28

6

2

Sodium Citrate

13

13

13

Observations:

There were two different levels of reactions, The 1st reaction did not fizz to much, the 2nd  had a rather vigorous reaction, as soon as the reactants were mixed.

Conclusion:

The results show that the first reaction, which gave out heat to its surroundings, was exothermic, and the second reaction, which took heat from its surroundings, was endothermic. After this has been established, a few more things may be noted.

Firstly, we know that the formula for energy evolved to be E = mc∆T, where m is mass of reactant, c is its specific heat capacity and T the temperature in Kelvin.

We disregard the use of Kelvin here as it does not change the result in any way. We also assume that the specific heat capacity of the reactant is 4.2 Joules/g cm, and the mass to be 25 grams.

Using the equation, the energy evolved from the first reaction is equal to 25 x 4.2 x 5, or 525 Joules. In the second reaction, we find the energy evolved to be 25 x 4.2 x 6, or 630 Joules. The copper sulphate was in a 1 mole/dm3 amount, and so 0.025 moles of it were used. Since the citric acid was in the same ratio, 0.025 moles of that was used as well.

525 Joules of energy was evolved from 0.025 moles of copper sulphate. Therefore from 1 mole, 525 x 1/0.025, or 21 Kilojoules would be its energy change per mole.

630 Joules of energy was evolved from 0.025 moles of citric acid. Therefore from 1 mole 630 x 1/0.025, or 25.2 Kilojoules would be its energy change per mole.

The equation for the reaction 1 is the following:

CuSO4(aq) + Zn(s) ZnSO4(aq) + Cu(s)

The equation for the second reaction is the following:

Sodium Carbonate(s) + Citric acid(aq) Sodium Citrate(aq) + Carbon Dioxide(g) + Water(l)

The enthalpy change for the first reaction is – 525 Joules, due to the reaction being exothermic, and the enthalpy change of the second reaction is 630 Joules, due to the reaction being endothermic.

This student written piece of work is one of many that can be found in our International Baccalaureate Chemistry section.

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