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# enthalpy change

Extracts from this document...

Introduction

Investigation 19 MEASURING ENTHALPY CHANGES Method: Part A 1) Put 100 cm3 of water at about 60 �C into a polystyrene cup by mixing boiling water from the kettle with cold water from the tap. 2) Dry about 25 g of ice with a piece of paper towel and weight them both. 3) Rapidly record the temperature of the water and transfer the ice to it, then record the mass of the paper towel and the water it has absorbed. 4) Stir the water ice mixture and record the temperature of the water as soon as all the ice has just melted. Part B 1) Take the polystyrene cup and use measuring cylinder to put 50 cm3 of 1 M aqueous copper sulphate in it. 2) Weigh out accurately about 5 g of powdered zinc into a weighing bottle. 3) Stir and record the temperature of the copper sulphate at half minute intervals for 2 minutes and then add the powdered zinc. 4) Record the temperature at half minute intervals until the temperature has been falling for ten consecutive recordings. ...read more.

Middle

c- specific heat capacity of H2O (J g-1 K-1) ?T- change of temperature (K) Mass of water=100 cm3 * 1 g cm-3= 100 g Qwater= m�c�?T Qwater=100g* 4.18 J g-1 K-1* 29.3 K=12247.4 J From the first law of thermodynamics we get the equation: Qwater= -Qice So the Q of ice is equal to -12247.4 J, so -12.2474 kJ. What is more, we know that the heat gained by ice was used to melt the ice first and then to raise the temperature of the whole solution: Qice=Qfus + (?Tice �c �mice) Qfus=Qice - (?Tice �c �mice) Qfus=-12247.4 - 30.5 K* 4.18 J g-1 K-1 * 17.9g Qfus= - 14529.71 J 1 mole H2O ice - x 0.99 moles of H2O ice - - 14529.71 J x= -14676.47 J mol-1 The enthalpy change for this reaction is -14676.47 J mol-1. Part B: enthalpy change for displacement reaction First step in the experiment was to create 1M copper sulphate. To do this solution, some calculations were needed: mCuSO4 � 5H2O = =250 g to create 50 cm3 1M solution I need: x=12.5g of copper sulphate So I dissolve 12.5 g copper sulphate in 50 cm3 of water. ...read more.

Conclusion

60.4 450.0 59.5 480.0 58.7 510.0 58.0 540.0 57.2 570.0 56.4 600.0 55.6 630.0 54.9 660.0 54.2 690.0 53.4 720.0 52.8 Rounded to 2 decimal place First two minutes of the temperature was measured for the solution of CuSO4 only. Then, the powdered zinc was added and the solution was stired rapidly until the maximum temperature has been reached ( which happened in 3.5 minute). Later on, the graph was plotted. Graph2: Graph showing the course of the measurement Using information from the table and extrapolations, I am able to calculate the enthalpy change. ?T= temp.max - temp.of CuSO4 ?T= 70.0-18.8 ?T= 51.2�C Q= m�c�?T where m- mass of solution (g) c- specific heat capacity of H2O (J g-1 K-1) ?T- change of temperature (K) m of solution=50 cm3 * 1 g cm-3= 50 g ?H=50 g* 4.18 J g-1 K-1 * 51.2 K = - 10700 J 1 mole CuSO4 - x 0.05 moles of CuSO4 - -10.7 kJ x= -214.0 kJ mol-1 The enthalpy change for this reaction is -214.0 kJ mol-1. CE: ?? ?? ?? ?? Gracja Kowalska kl. 2 IB 1 ...read more.

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