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Enthalpy of formation of calcium carbonate

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Introduction

EXPERIMENT 6 Enthalpy of formation of calcium carbonate Objective To determine the enthalpy of formation of calcium carbonate Procedures A. Reaction of calcium with dilute hydrochloric acid 1. 1.0909 g of calcium metal was weighed out accurately. 2. 100 cm3 of approximately 1 M hydrochloric acid was pipetted.and placed in a plastic beaker. 3. The initial temperature of the acid was determined 4. The weighed calcium was added into the acid and stirred thoroughly with the thermometer until all the metal had reacted. 5. The maximum temperature attained by the solution was recorded. 6. The experiment was repeated with 1.0538g calcium metal. Results: Experiment no. 1 2 Mass of Ca used/ g 1.0909 1.0538 Initial temp. of solution/ ? 27 26 final temp. of solution/ ? 55 52 Temperature change/ ? 28 26 Calculations and Discussion: 1. What does the term "heat of formation" of a substance mean? Heat of formation refers to the heat change when one mole of a substance is formed from its constituent elements is their standard states under standard conditions. 2. What are "standard conditions" for thermochemical calculations? Standard conditions is defined as elements or compounds appear in their normal physical states at a pressure of 1 atm (101325 Nm-2/760mmHg) ...read more.

Middle

2. 100 cm3 of approximately 1 M hydrochloric acid was pipetted into another beaker. 3. The acid was poured on the carbonate in the plastic beaker. 4. The solution was stirred briskly with the thermometer and the maximum temperature reached by the solution. was recorded. 5. The experiment was repeated with 2.7400g of dry powdered calcium carbonate. Results: Experiment no. 1 2 Mass of CaCO3 used/ g 3.0940 2.7400 Initial temp. of solution/ ? 26 25 final temp. of solution/ ? 28 27 Temperature change/ ? 2 2 Calculations and Discussion: 1. Write an ionic equation for the reaction taken place. (Call this Equation 3) CO32-(aq.) + 2 H+(aq.) ? CO2(g) + H2O(l) 2. Calculate the average heat evolved by one mole of calcium carbonate. (Making the same assumptions as in Part A) For the first experiment: ?Energy evolved by the reaction= Energy absorbed by the acid ?By E = mc?T, ?H per mole of calcium carbonate = [(100/1000)(4200)(2)]/[(3.0940/(40.08+12.01+16x3)] =840 /[(3.0940)/(100.09)] =-27174 J mol-1 =-27.174 kJmol-1 For the second experiment: ?Energy evolved by the reaction= Energy absorbed by the acid ?By E = mc?T, ?H per mole of calcium carbonate = [(100/1000)(4200)(2)]/[(2.7400/(40.08+12.01+16x3)] =840 /[(2.7400)/(100.09)] =-30685 J mol-1 =-30.685 kJmol-1 Average ?H per one mole of calcium (?Hy) ...read more.

Conclusion

In other words, an energy change is path independent, only the initial and final states being of importance. This path independence is true for all state functions 8. State the law which you have used in order to answer Question (7) depends? Why is this principle useful? The law of conservation of energy states that energy can neither be created nor destroyed but can be changed from one form to another.In order to achieve the answer, Hess's law is used. Hess's law states that the total enthalpy change of a reaction is independent of the route by which the reaction takes place. In other words, the standard enthalpy change of a reaction depends on the differences in standard enthalpy between the reactants and the products. It means that the enthalpy of the reaction system is conserved. As the absolute enthalpy of a substance is not possible to be determined and only the difference between reactants and products can be measured experimentally. This law helps us to define the standard enthalpy change of a reaction. Conclusion The enthalpy of formation of calcium carbonate is -1073.6kJ mol-1 Reference http://hk.knowledge.yahoo.com/question/?qid=7006100200879 http://hk.knowledge.yahoo.com/question/question?qid=7007111800043 http://www.answers.com/8.%09Should+we+measure+the+volume+of+acid+with+a+measuring+cylinder%3F+Why%3F http://hk.search.yahoo.com/search/kp?ei=UTF-8&p=word%E6%89%93%E5%88%86%E7%B7%9A&rd=r1&fr2=tab-web&fr=FP-tab-web-t F.6 Chemistry Notes Section III by Ms Sin W L THE END ?? ?? ?? ?? F.6 Chemistry/TAS 6/P.1(7) ...read more.

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Response to the question

Good scientific essay. The response to the different questions are adequate and presented to a high level of scientific correctness. Definitely could be used as a clear and concise building block for anyone looking for ideas about calcium carbonate combustion.

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Response to the question

Good scientific essay. The response to the different questions are adequate and presented to a high level of scientific correctness. Definitely could be used as a clear and concise building block for anyone looking for ideas about calcium carbonate combustion.

Level of analysis

The mass of calcium and how it is weighed out is not described very well, and the candidate may have included the mass of the weighing boat in the mass of calcium used. The analysis used is to a high level and all the calculations and scientific definitions are correct. The candidate could have improved their grade by calculating percentage errors in the experiment for the equipment used. References should have been correctly cited throughout the text. Scientific terms used are to a good standard.

Quality of writing

All punctuation and grammar seems correct but sometimes one or two words have incorrect endings or the 's' missed off. Spelling apart from this seems fine.


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Reviewed by skatealexia 15/04/2012

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