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Using Calorimeter Techniques to Indirectly Determine An Enthalpy Change Using Hess Law

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Introduction

Name: Vo Ngoc Kieu Duyen - Cher Date : April 5th 2011 IB Chemistry HL Mr. Brendt Bly Internal Assessment: Title: Using Calorimeter Techniques to Indirectly Determine An Enthalpy Change Using Hess' Law Aim: Determine an enthalpy change using Hess' Law and calorimeter techniques. Procedure: IB Chemistry Investigations - Volume 1 - Core. Data Collection and Processing: Table 1: The volume of 2 mol dm-3 hydrochloric acid and mass of sodium hydrogen carbonate and mass of weighing bottle & sodium hydrogen carbonate when measuring. Volume of Hydrochloric acid (HCL) 100.5 � 0.01 grams Mass of Sodium hydrogen carbonate 14.08 � 0.01 grams Mass of weighing bottle and NaHCO3 41.73 � 0.01 grams Mass of weighing bottle before adding NaHCO3 27.62 � 0.01 grams Mass of weighing bottle after putting NaHCO3 into Hydrochloric acid (HCL) 27.62 � 0.01 grams Table 2: The temperature change during the reaction of Hydrochloric acid and Sodium hydrogen Carbonate Time (s) ...read more.

Middle

and Sodium Carbonate (Na2CO3) Calculations: Part 1: HCl + NaHCO3 reaction Change in temperature (?T): ?T = 18.2 �C - 28.0 �C ?T = -9.85 � 1 �C Q = mc(?T) Q = (-9.8 �C)(4.18 J/g�C)(100.5 g) Q = 4116.8 J Q � - 4.12 kJ Sign of Q must be opposite with the sign of delta H. Therefore, Q = 4.12 kJ. Mol NaHCO3 = 14.08 g NaHCO3 ( = 0.167 mol � 0.17 mol NaHCO3 ?H = = 24.23 kJ mol-1 Part 2: HCl + Na2SO3 reaction Change in temperature (?T): ?T = 34.1 �C - 24.2 �C ?T = 9.9 � 1 �C Q = mc(?T) Q = (9.9 �C)(4.18 J/g�C)(100.5 g) Q = 4158.891 J Q � 4.16 kJ Sign (charge) of Q must be opposite with the sign (charge) of delta H. Therefore, Q = -4.16 kJ. Mol Na2SO3 = 8.08 g Na2SO3 ( = 0.076 mol � 0.08 mol Na2SO3 ?H = = - 5.2 kJ mol-1 Enthalpy change calculation: 2NaHCO3 (s) ...read more.

Conclusion

Since I have a high percentage error of 87%, I came up with some random errors that could have occurred throughout our experiment: I have to use an analogue thermometer and I have to open the cup to check the temperature so the reaction might not have the accurate result it is affected by the surroundings. The heat might have spread out to the atmosphere around it when I opened the cup to check the temperature in the second experiment. In the first one, the temperature might be affected by the heat from the surroundings and it couldn't reach the coolest point. Next time, I should use an electric probe (digital thermometer) to minimize the heat loss or heat gain to/from the surroundings. Another thing that has could gone wrong is that throughout the experiment, I put the substance in the acid bit by bit and I moved the cup in circular motions a lot; that could be an error. Because the acid didn't have the enough amount of sodium to react so the results were not very accurate. ...read more.

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