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The aims of this experiment are to measure the heat of decomposition of hydrogen peroxide the heat capacity of calorimeter and calculate the enthalpy of decomposition of hydrogen.

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Introduction

´╗┐SINGAPORE POLYTECHNIC SCHOOL OF CHEMICAL LIFE SCIENCES Diploma of Applied Chemistry with Pharmaceutical Science Experiment 3 Heat of Decomposition of Hydrogen Peroxide Date of Experiment: 25/11/10 CP4117 Desmond Seah (P1006812) Year of Study: Year 1 DACP/FT AY 10/11 ________________ Content Page Synopsis Page 1. Introduction 1-2 2. Theory 2-6 3. Procedure 7 4. Results and calculation 8-10 5. Discussion 10-11 6. Conclusion 12 7. Recommendation References List of Illustration S/N Figures and Tables Page Number 1 Simple calorimeter 4 2 Bomb calorimeter 5 3 Suggested setup for simple calorimeter 11 Synopsis The central objectives of this experiment are to measure the heat of decomposition of hydrogen peroxide, the heat capacity of the calorimeter and calculate the enthalpy of decomposition of hydrogen peroxide. The heat capacity of the calorimeter is established by measuring the temperature change that occurs when a known and similar amount of hot water is added to the cold water in the calorimeter. The decomposition of hydrogen peroxide was performed by adding the catalyst Fe(NO3)3 to the hydrogen peroxide in calorimeter to accelerate and initiate the decomposition reaction. The enthalpy of decomposition of hydrogen peroxide was calculated by adding the heat change for solution and calorimeter together divided by the number of moles of hydrogen peroxide reacts. Conclusively, the experiment was a success as the error is considerably small (5.02%) with the enthalpy of -89.9kJ/mol. However, by adopting the humble suggestion I have stated in the discussion, I am confident we will be able to achieve better accuracy and precision with repetition of the experiment. 1. Introduction The aims of this experiment are to measure the heat of decomposition of hydrogen peroxide the heat capacity of calorimeter and calculate the enthalpy of decomposition of hydrogen. The value of the enthalpy change ?H reported for a reaction is the amount of heat liberated or absorbed when reactants are converted to products at the same temperature and in the molar amounts represented by coefficients in the balanced equation. ...read more.

Middle

The reaction is carried out inside the vessel, and heat evolved or absorbed is calculated from the temperature change. Because the pressure inside the calorimeter is constant (atmospheric pressure), the temperature measurement makes it possible to calculate the enthalpy change ΔH during a reaction. Figure 1: Simple calorimeter (McMurry & Fay 2003). A somewhat more complicated device called a bomb calorimeter is used to measure the heat released during a combustion reaction, or burning flammable substance. (More generally, a combustion reaction or burning of a flammable flame.) The sample is placed in an insulated, water-filled container (Fig 2). The reactants are ignited electrically, and the evolved heat is calculated from the temperature change of the surrounding water. Since the reaction takes place at constant volume but not constant pressure, the measurement provides a value of ΔE rather than ΔH. Figure 2: Bomb calorimeter (McMurry & Fay 2003). How can temperature change inside a calorimeter be used to calculate ΔH for a reaction? When a calorimeter and contents absorb a given amount of heat, the temperature rise that results depends on the calorimeter’s heat capacity. Heat capacity(C) is the amount of heat required to raise the temperature of an object or substance a given amount, a relationship that can be expressed by the equation Where q is the quantity of heat transferred and ΔT is the temperature change (ΔT= T final – T initial). The greater the heat capacity, the greater the amount of heat needed to produce a given temperature change. A bathtub full of water, for instance, has greater heat capacity than a coffee cup full, and it therefore takes far more heat to warm the tubful than the cupful. The exact amount of heat absorbed is equal to the heat capacity times the temperature rise: q = C×ΔT Heat capacity is an extensive property, so its value depends on both size of an object and its composition. ...read more.

Conclusion

They are, however, useful only rough measurements are required. Therefore, in my humble opinion I would recommend the use of burette to measure out the volume of water needed to greater accuracy. Furthermore, the simple calorimeter we have used in the experiment poorly insulates the system from the surrounding and significant heat will be lost from the system to the surrounding. Therefore, we could stack two Styrofoam cups on top of one another in order to trap air and create a layer of insulation shown in figure 3 or even better if we can use bomb calorimeter. Figure 3: Suggested setup for simple calorimeter. Human errors such as slowness and parallax errors affect the reading. For instance, when we are told to cover the calorimeter immediately, there will still be delay of fraction of a second or more which will result in loss of heat and temperature will differ from the ideal. While taking reading from the thermometer or measuring out the volume of reactants need with measuring cylinder parallax errors might occurs and we have to careful while reading the meniscus level. All types of volumetric glassware have a cylindrical shape in the measuring region which causes the surface of most liquids whose volumes are to be measured to be curve downwards. Take reading from the bottom of the curved surface called meniscus with your eyes at the same level. To read the position of the meniscus, the eye must be at the same level as the meniscus, in order to avoid errors due to parallax. 6. Conclusion The objectives of this experiment such as the heat of decomposition of hydrogen peroxide, the heat capacity of calorimeter and enthalpy of decomposition of hydrogen peroxide were measured and calculated. The heat capacity of the calorimeter was 8.374J/oC and the enthalpy of decomposition of hydrogen peroxide was -89.9kJ/mol. Therefore, we have successfully met the literature value with an error of approximately 5.02%. Therefore, I have stated a few suggestions that may be put to use in if we can repeat the experiment to achieve a more accurate and precise value of enthalpy. 8. ...read more.

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