To determine enthalpy change Essay Example for Free

To determine atomic number 1 change EssayChemistry science laboratory report 1) Experiment No 8A 2) Objective To determine the wake up of formation of atomic number 20 carbonate. 3) Date twenty-sixth Nov, 2010 4) Theory The experiment consists of 2 segments a) In the 1st part, an accurately weighed known mass of atomic number 20 is added to a given dilute hydrochloric acerbic. During the addition, the following occurs Ca(s) + 2H+(aq) Ca2+(aq) + H2(g) With the serve well of the data of waken change of the solution mixture, the come heat evolved by one mole of calcium during the reaction tolerate be calculated. b) In the second part, an accurately weighed known mass of calcium carbonate is added to a given dilute hydrochloric acid. During the addition, the following occurs CaCO3(s) + 2H+(aq) Ca2+(aq) + CO2(g) + H2O(l) With the help of the data of heat change of the solution mixture, the average heat evolved by one mole of calcium carbonate during the reaction can be c alculated. After that, by using a suitable energy-cycle diagram, and applying Hesss law, the heat formation of formation of calcium carbonate can be calculated.5) Procedure Please refer to the lab. manual 6) Data 1st Part Reaction of calcium with dil. Hydrochloric acid Experiment No 1 2 jackpot of Ca used / g 0. 53 0. 51 Volume of hydrochloric acid used 100cm3 second Part Reaction of calcium carbonate with dil. Hydrochloric acid Experiment No 1 2 Mass of CaCO3 used / g 2. 13 2. 05 Molar mass of calcium carbonate = 100 g/mol Volume of hydrochloric acid used = 100 cm3 7) Calculation Note No temperature drop can be observed after the max temperature is attained for 4 readings.Note No temperature drop can be observed after the max temperature is attained for 4 readings. Extrapolation procedure cannot be done. Therefore, the temperature change of 1st part exp. = 28-25 = +3oC the temperature change of 2nd part exp = Enthalpy change in 2nd parts reaction Hf H2O(l) = -242000 J mol-1 Hf CO 2(g)= -393500 J mol-1 source physical chemisty I of Fillans By Hesss law HfCaCO3(s) = H1 + Hf H2O(l) + Hf CO2(g) H2 = -688. 79 kJ mol-1 8) Discussion 1. Why is the exact concentration of hydrochloric acid unimportant? The exact concentration of the hydrochloric acid was unimportant as it was present in excess, that was, to provide enough H+(aq) to react with calcium.At the said(prenominal) time, the exact concentration of hydrochloric acid would affect the calculation afterwards. 2. State the law which you use for calculating the heat of formation of calcium carbonate. On which thermodynamic principle does it depends? The law used was the Hesss law. It depends on the standard enthalpy change of a reaction is independent of the route by which the chemical reaction takes place, which only depends on the difference between the standard enthalpies of reactants and products, i. e. conservation of energy. 3. Why is this law useful?This principle is useful as the standard enthalpy change of some reaction might not be able to line up directly, and thus Hesss law can be used and the standard the enthalpy change of the reaction can be calculated indirectly by this method. 4. Discuss the possible sources of errors. State how to minimize the possible errors. A. The substantiality labeled calcium is suspected to be calcium oxide, which show white color but not grey shinny color. B. Heat produced the reaction might heat up the air inside the beaker, which cannot be avoided. C. Error in reading thermometer D. Error in weighing.