The change in enthalpy for the combustion of magnesium metal Essay exam

The change in enthalpy for the combustion of magnesium metal Abstract ======== Hess’s law of heat summation states that the value of DH for a reaction is the same whether it occurs directly or as a series of steps. This principle was used to determine the change in enthalpy for a highly exothermic reaction, the combustion of magnesium metal. Enthalpy changes for the reactions of Mg in HCl (aq) and MgO (s) in HCl (aq) were determined experimentally, then added to that for the combustion of hydrogen gas to arrive at a value of –587 kJ/mol Mg. Compared with the accepted value of –601.8 kJ/mol Mg, our experimental error was 2.46%. Introduction In this investigation the change in enthalpy will be determined from the following equation: 2Mg + O2  ® 2MgO, but in an indirect manner. Magnesium metal burns with a bright extremely hot flame to produce magnesium oxide. It would be difficult to measure the heat of the reaction since the reaction is rapid and occurs at a high temperature (LeMay et al, 1996). So, to determine the change in enthalpy we will employ Hess’s Law of heat summation: It states that the value of DH for a reaction is the same whether it occurs directly or as a series of steps (LeMay et al, 1996). We will perform the two following reactions: Mg + 2HCl  ® MgCl2 + H2 and MgO + 2HCl  ® MgCl2 + H2O, determine their enthalpy changes (DHs), and they will then be â€Å"added† to that of a given equation, the combustion of water, H2 + 1/2 O2  ® H2O DH=-285.5 kJ/mol. In this investigation we will be working with potentially dangerous chemicals and safety precautions must be made. Magnesium oxide is a respiratory and eye irritant, the dust must not be inhaled and all work with MgO should be conducted in the fume hood ( Cartwright,... ...te, only having a 2.46% error. These errors may be accounted for by inaccurate measurements, mathematical mistakes, incomplete reactions, poor heat collection, incorrect recording of data, and poorly calibrated tools. To avoid such error one should label all materials, check each tool before use, take extra care in reading and recording of measurements, double check all calculations, and most of all be patient, labs take time and a rushed procedure leads to inaccurate data and incorrect analysis. Sources Cited Cartwright, H.(last revised 2002, November 5). Chemical and other Safety Information. The Physical and Theoretical Chemistry Laboratory, Oxford University. [online]. (accessed 2002, December, 4) LeMay, H.E.,Beall, H., Roblee, K.M., and Brower, D.C. (1996).Chemistry: Connections to our changing world, Laboratory Manual. Upper Saddle River, NJ: Prentice Hall. The change in enthalpy for the combustion of magnesium metal Essay exam The change in enthalpy for the combustion of magnesium metal Abstract ======== Hess’s law of heat summation states that the value of DH for a reaction is the same whether it occurs directly or as a series of steps. This principle was used to determine the change in enthalpy for a highly exothermic reaction, the combustion of magnesium metal. Enthalpy changes for the reactions of Mg in HCl (aq) and MgO (s) in HCl (aq) were determined experimentally, then added to that for the combustion of hydrogen gas to arrive at a value of –587 kJ/mol Mg. Compared with the accepted value of –601.8 kJ/mol Mg, our experimental error was 2.46%. Introduction In this investigation the change in enthalpy will be determined from the following equation: 2Mg + O2  ® 2MgO, but in an indirect manner. Magnesium metal burns with a bright extremely hot flame to produce magnesium oxide. It would be difficult to measure the heat of the reaction since the reaction is rapid and occurs at a high temperature (LeMay et al, 1996). So, to determine the change in enthalpy we will employ Hess’s Law of heat summation: It states that the value of DH for a reaction is the same whether it occurs directly or as a series of steps (LeMay et al, 1996). We will perform the two following reactions: Mg + 2HCl  ® MgCl2 + H2 and MgO + 2HCl  ® MgCl2 + H2O, determine their enthalpy changes (DHs), and they will then be â€Å"added† to that of a given equation, the combustion of water, H2 + 1/2 O2  ® H2O DH=-285.5 kJ/mol. In this investigation we will be working with potentially dangerous chemicals and safety precautions must be made. Magnesium oxide is a respiratory and eye irritant, the dust must not be inhaled and all work with MgO should be conducted in the fume hood ( Cartwright,... ...te, only having a 2.46% error. These errors may be accounted for by inaccurate measurements, mathematical mistakes, incomplete reactions, poor heat collection, incorrect recording of data, and poorly calibrated tools. To avoid such error one should label all materials, check each tool before use, take extra care in reading and recording of measurements, double check all calculations, and most of all be patient, labs take time and a rushed procedure leads to inaccurate data and incorrect analysis. Sources Cited Cartwright, H.(last revised 2002, November 5). Chemical and other Safety Information. The Physical and Theoretical Chemistry Laboratory, Oxford University. [online]. (accessed 2002, December, 4) LeMay, H.E.,Beall, H., Roblee, K.M., and Brower, D.C. (1996).Chemistry: Connections to our changing world, Laboratory Manual. Upper Saddle River, NJ: Prentice Hall.