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# Enthalpy changes

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Introduction

Enthalpy Changes Analysis Results Recording Test 1 Test 2 Test 3 Units Mass of CaCO3 + weighing bottle 3.50 3.52 3.50 g Mass of empty weighing bottle 1.04 1.01 1.00 g Mass of CaCO3 used 2.50 2.50 2.50 g Temperature of acid initially 21.50 22.00 21.00 �C Temperature of solution after mixing 24.00 24.00 23.00 �C Temperature change during reaction 2.50 2.00 2.00 �C Mass of CaO + weighing bottle 2.52 2.30 2.40 g Mass of empty weighing bottle 1.12 0.90 1.00 g Mass of CaO used 1.40 1.40 1.40 g Temperature of acid initially 22.00 22.50 21.00 �C Temperature of solution after mixing 32.50 32.50 30.00 �C Temperature change during reaction 10.50 10.00 9.00 �C ?H1 The Reaction between CaCO3 + HCL J = m.c. ?T is used to calculate the energy produced using heat capacity of HCL, and 50ml of HCL with the temperature change in the reaction. J = m.c. ?T 50 x 4.2 x 2.5 = -525 J 50 x 4.2 x 2 = -420 J 50 x 4.2 x 2 ...read more.

Middle

If, say 1�C of heat loss was saved lost on each of the above reactions then the resultant enthalpy change would have been very different as we can see by doing the calculations below ?H1 J = m.c. ?T 50 x 4.2 x 3.5 = -735 J 50 x 4.2 x 3 = -630 J 50 x 4.2 x 3 = -630 J AVG = -665 J 665 = -26.6 kJ/mole 0.025 If we do the same for the ?H2 reaction then we get -91 kJ/mole. If we then use Hess's cycle to find ?H3 then we get 117.6 kJ/mole. This shows just how 1�C of heat loss can affect the results of the reaction. To combat this next time I will conceal the experiment in a polystyrene cup. Polystyrene has excellent heat absorbing qualities, and would ensure that little heat is lost during the reaction. I could also put a lid on the beaker during the reaction. ...read more.

Conclusion

?H1 J = m.c. ?T 53 x 4.2 x 2.5 = -556.5 J 53 x 4.2 x 2 = -445.2 J 53 x 4.2 x 2 = -445.2 J AVG = -482.3 J 482 = -19.28kJ/mole 0.025 If we do the same for the ?H2 reaction then we get -87.5 kJ/mole. If we then use Hess's cycle to find ?H3 then we get 68.22kJ/mole. This shows just how 3ml more of HCL could affect the reaction. It could affect it even more as well. If there was a =3ml error on the first reaction and a -3ml on the second then we get 77.6kJ/mole. To stop this from happening again I could use a 50ml pipette to measure the solution to a much smaller resolution Another error in measurements was that the thermometer's resolution wasn't small enough. We could only detect a 0.5�C change in temperature. As we have seen before a temperature error can drastically change the results. To avert this problem next time, I cold use a loggit temperature probe. This is an electronic device that measure temperature to 2 d.p. This would make my results much more reliable. ...read more.

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