Thermodynamic Investigation of the Joule-Thompson Effect
Thermodynamic Investigation of the Joule-Thompson Effect and Coefficient Determination for Helium and Carbon Dioxide
Niki Spadaro, Megan Cheney, and Jake Lambeth
University of North Florida, CHM4410C Fall 2010
The Joule-Thomson coefficient explains the behavior of any real gas when changes in intensive properties, such as temperature and pressure, occur. The coefficients for helium and carbon dioxide were determined using a Joule-Thomson apparatus that created constant enthalpy within the system. Using literature values for the coefficients at room temperature, the experimental results allow examination of each gas’s unique nature.
Introduction Enthalpy is a critical study in thermodynamics. It is a measurement of a system’s internal energy (U) and work associated with pressure and volume:
H = U + PV (1)
Isenthalpic conditions were established in the experiment by use of the Joule-Thomson apparatus, in which a glass filter divided a glass cylinder into two chambers. This constant enthalpy can be explained by a series of equations that apply to the system. (Smith, pp.125-127). The First Law of Thermodynamics describes the internal energy of a system as a function of transferred heat (q) and P-V work (w) done: ∆U = dq + dw = dq - PdV (2)
Since the experimental procedure was conducted in an adiabatic environment, no heat transfer occurred and the internal energy depended only on work. The total work of the system is the sum of the work done on each side of the chamber to maintain equilibrium. The latter statements allow alteration of equation 2: ∆U = U2 – U1 = ∑dw = dw1 + dw1 = - ∫P1dV - ∫P2dV (3)
U2 – U1 = P1V1 – P2V2 (a.) ( U1 + P1V1 = U2 + P2V2 (b.) (4a,b)
Incorporating equation 3b. into equation 1, it is apparent that the work being done on each side is the same. There is no
Niki Spadaro, Megan Cheney, and Jake Lambeth
University of North Florida, CHM4410C Fall 2010
The Joule-Thomson coefficient explains the behavior of any real gas when changes in intensive properties, such as temperature and pressure, occur. The coefficients for helium and carbon dioxide were determined using a Joule-Thomson apparatus that created constant enthalpy within the system. Using literature values for the coefficients at room temperature, the experimental results allow examination of each gas’s unique nature.
Introduction Enthalpy is a critical study in thermodynamics. It is a measurement of a system’s internal energy (U) and work associated with pressure and volume:
H = U + PV (1)
Isenthalpic conditions were established in the experiment by use of the Joule-Thomson apparatus, in which a glass filter divided a glass cylinder into two chambers. This constant enthalpy can be explained by a series of equations that apply to the system. (Smith, pp.125-127). The First Law of Thermodynamics describes the internal energy of a system as a function of transferred heat (q) and P-V work (w) done: ∆U = dq + dw = dq - PdV (2)
Since the experimental procedure was conducted in an adiabatic environment, no heat transfer occurred and the internal energy depended only on work. The total work of the system is the sum of the work done on each side of the chamber to maintain equilibrium. The latter statements allow alteration of equation 2: ∆U = U2 – U1 = ∑dw = dw1 + dw1 = - ∫P1dV - ∫P2dV (3)
U2 – U1 = P1V1 – P2V2 (a.) ( U1 + P1V1 = U2 + P2V2 (b.) (4a,b)
Incorporating equation 3b. into equation 1, it is apparent that the work being done on each side is the same. There is no
References: 1. Engel, T. & Reid, P. Physical Chemistry, 2nd ed. 2006, Pearson Prentice Hall, New Jersey, pp 3. Gould, H. & Tobochnik, J. Statistical and Thermal Physics (STP). 2009, Princeton University Press, New Jersey, pp. 31-106. 4. Smith, E. Basic Chemical Thermodynamics, 5th ed. 2004, Imperial College Press, London, pp. 125-128.