Determination of Heat of Solution
DETERMINATION OF THE HEAT OF SOLUTION BY THE VANT HOFF ISOCHORE METHOD
Jan Vincent Arafiles, Merry Joy Arzaga, Anne Louise Ayson, Lovely Jenny Buenaflor
Group 2 3A-Biochemistry chem401 laboratory
ABSTRACT
Thermodynamic values can be determined using the Vant Hoff isochore method. This method entails the use of equilibrium systems to determine the change in enthalpy of the solution, which can b related to the change in internal energy of the solution. The van 't Hoff isochore relates the equilibrium constant of a chemical reaction at one temperature to the equilibrium constant of the same reaction at a different temperature, allowing it to be worked out for all temperatures if it is known for one. The experiment used the solution of toluene and naphthalene to determine the change in enthalpy. The mole fractions and the tempterature of recrylstallizations were graphed and the slope was determined. From the slope the change in enthalpy was determined to be 3.45J. This implies that energy is absorbed by the system.
INTRODUCTION Solutions are very common in nature and in the chemistry lab. They provide the environment in which many chemical reactions occur. Thus, in the chemistry classroom and lab, we are immensely interested in solutions, especially liquid solutions. Solutions are defined as homogeneous mixtures of pure substances in which no precipitation or settling occurs. We often think of solutions as liquids, but we can have solutions of solids (alloys), gases (air is a solution of nitrogen, oxygen, carbon dioxide, and a number of other gases), and a combination of states such as liquid and solid metals (amalgams) and liquids and gases (nitrogen in the blood, carbonated beverages). The ease of dissolution is dependent on two factors: (1) the change in disorder or randomness (entropy) of the system and (2) the change in the energy of the process (heat of solution). The process is generally favored when the degree of randomness increases
Jan Vincent Arafiles, Merry Joy Arzaga, Anne Louise Ayson, Lovely Jenny Buenaflor
Group 2 3A-Biochemistry chem401 laboratory
ABSTRACT
Thermodynamic values can be determined using the Vant Hoff isochore method. This method entails the use of equilibrium systems to determine the change in enthalpy of the solution, which can b related to the change in internal energy of the solution. The van 't Hoff isochore relates the equilibrium constant of a chemical reaction at one temperature to the equilibrium constant of the same reaction at a different temperature, allowing it to be worked out for all temperatures if it is known for one. The experiment used the solution of toluene and naphthalene to determine the change in enthalpy. The mole fractions and the tempterature of recrylstallizations were graphed and the slope was determined. From the slope the change in enthalpy was determined to be 3.45J. This implies that energy is absorbed by the system.
INTRODUCTION Solutions are very common in nature and in the chemistry lab. They provide the environment in which many chemical reactions occur. Thus, in the chemistry classroom and lab, we are immensely interested in solutions, especially liquid solutions. Solutions are defined as homogeneous mixtures of pure substances in which no precipitation or settling occurs. We often think of solutions as liquids, but we can have solutions of solids (alloys), gases (air is a solution of nitrogen, oxygen, carbon dioxide, and a number of other gases), and a combination of states such as liquid and solid metals (amalgams) and liquids and gases (nitrogen in the blood, carbonated beverages). The ease of dissolution is dependent on two factors: (1) the change in disorder or randomness (entropy) of the system and (2) the change in the energy of the process (heat of solution). The process is generally favored when the degree of randomness increases
References: [1] Rossotti and H. Rossotti, The Determination of Stability Constants, McGraw-Hill, 1961 [2] Atkins, Peter; De Paula, Julio (2006-03-10). Physical Chemistry (8th ed.). W.H. Freeman and Company. p. 212. [3] NonLinear vant hoff solubility. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T7W-479CM6F-3M&_user=10&_coverDate=01%2F31%2F1984&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1474224563&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bc9cac9220a53d018a21b381170d2732&searchtype=a. taken September 28, 2010 [4] Vant Hoff Isochore. http://www.scenta.co.uk/tcaep/nonxml/science/equations/details/van 't%20Hoff%20isochore.htm taken September 28, 2010.