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# To determine the enthalpy of reaction.

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Introduction

Lewisham College Zahra Hussien As chemistry Assessor: Bernice Ferdinand Science investigation for OCR coursework As chemistry Title To determine the enthalpy of reaction Introduction The enthalpy change of reaction is the enthalpy change when amount of reactants react together under standard conditions to give products in their standard states. The heat change might be exothermic or endothermic. Exothermic reactions: Heat flows from the system to the surroundings. The value will be negative. Endothermic reactions: Heat flows from the surroundings into the system. The value will be positive. Aim The purpose of this experiment is to determine the enthalpy of the reaction for a displacement reaction: * CaCo3(s) + 2HCl(aq)? CaCl2(aq) + Co2(ga) + H2O(l) * CaO(s) + 2HCl(aq) ? CaCl2(aq) + H2O(l) By adding 2 mol/dm3 of HCl to a CaCo3 and CaO, and measure the temperature changes and calculates the enthalpy change for the reaction. Prediction I predict from the experiment I am going to do, I expect the reaction is going to be exothermic reaction in both CaCo3 and CaO. ...read more.

Middle

? CaCl2(aq) + H2O(l) * Find the number of moles for CaO n = m/M n = 2.52/52 n = 0.0485mol * Heat evolved during the reaction (?H2) ?H2 = mc?T2 ?H2 = 1.5 x 4.2 x (40.5oc-18oc) ?H2 = 141.75J ?H2 = 0.14175 kJ * Heat evolved per mol ?H2/n = 0.14175 kJ /0.0485 ?H2 = 2.92KJ/mol * ?H3 = ?H1 - ?H2 ?H3 = 0.84KJ/mol - 2.92KJ/mol ?H3 = -2.08KJ/mol > Glass beaker * CaCo3(s) + 2HCl? CaCl2(aq) + Co2(ga) + H2O(l) * Find the number of moles for CaCo3 n = m/M n = 2.52/100 n = 0.0252mol * Heat evolved in the reaction ?H1 = mc?T1 ?H1= 2.52 x 4.2 x (21oc-20oc) ?H1 = 10.584J ?H1 = 0.010584 kJ * Heat evolved per mol ?H1/n = 0.010584KJ/0.0252mol ?H1 = 0.42 KJ/mol * CaO(s) + 2HCl(aq) ? CaCl2(aq) + H2O(l) * Find the number of moles for CaO n = m/M n = 2.52/52 n = 0.0485mol * Heat evolved during the reaction (?H2) ?H2 = mc?T2 ?H2 = 1.5 x 4.2 x (36.5oc-18oc) ...read more.

Conclusion

* I use one thermometer to avoid any source of error. * I make sure the equipments were clean and dry. * I used a different weighing bottle to measure CaCO3 and CaO. * I was controlling my self when I was transferring those powders. However, there are a number of errors might happen during the experiment: 1. There is a transfer error; some amount of CaCO3, CaO remain in the weighing bottle while I was transferring to the glass beaker and polystyrene. 2. Reading of the thermometer (I can only read to accuracy of nearest degree). 3. Measuring of the weight of CaCO3 and CaO. 4. Some errors are likely to come from measurements. A source of error would be parallax error, which would involve the meniscus. Suggestions and Improvements - To create a more accurate experiment in the future, several precautions or alterations can be made: * Cover both polystyrene and glass beaker to avoid heat loss to the environment * Stir the solution in the same manner to get the maximum heat lost. * It will be a god idea to do the investigation more than one so that an average of heat loss could be calculated. ...read more.

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1. ## Exothermic and endothermic reactions

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