Enthalpy & Entropy
Experiment
ENTHALPY AND ENTROPY OF ZINC WITH COPPER SULFATE The CCLI Initiative Computers in Chemistry Laboratory Instruction
LEARNING OBJECTIVES The learning objectives of this experiment are to. . . ! ! determine changes in enthalpy and entropy of the reaction of zinc with copper sulfate using two methods: electrochemistry and calorimetry. compare the enthalpy values obtained by the two methods. BACKGROUND Thermodynamics is concerned with energy changes that occur in chemical and physical process es. The enthalpy and entropy changes of a system undergoing such processes are interrelated by the change in free energy, ªG, according to the equation
ªG
=
ªH - T ªS
(1)
This investigation focuses on the reaction Zn(S ) + CuSO4(aq)
Y
ZnSO4(aq) + Cu(S )
(2)
ªG will be calculated from the ªH and ªS values obtained electrochemically. The validity of Equation (1) will be tested by comparing the value of ªH obtained electrochemically with the value of ªH obtained calorimetrically for the same reaction. The electrochemical method The electrochemical method offers simple and accurate means for the determination of thermodynamic quantities. A simple electrochemical cell is constructed in a Chem-Carrou-Cell™ plate as shown in Figure 1. Cu(S )/CuSO4 (aq) || Zn(S )/ZnSO4(aq) (3)
FiªG ure 1: Set-up for measuring E versus temperature.
1
The CCLI Initiative
The overall galvanic cell reaction is Zn(S ) + Cu2+ (aq) Y Zn2+(aq) + Cu(S ) and it is essentially the same as that taking place in the calorimeter. The quantity of the electrical energy, F , produced or consumed during the electrochemical reaction is a constant measured per mole of electrons, and can be accurately measured. The free energy change, ªG , of an electrochemical reaction is related to the voltage, E, of the electrochemical cell by the equation (4)
ªG where and
= -nFE n
(5)
F
= the number of moles of electrons transferred in a redox reaction. = Faraday's
ENTHALPY AND ENTROPY OF ZINC WITH COPPER SULFATE The CCLI Initiative Computers in Chemistry Laboratory Instruction
LEARNING OBJECTIVES The learning objectives of this experiment are to. . . ! ! determine changes in enthalpy and entropy of the reaction of zinc with copper sulfate using two methods: electrochemistry and calorimetry. compare the enthalpy values obtained by the two methods. BACKGROUND Thermodynamics is concerned with energy changes that occur in chemical and physical process es. The enthalpy and entropy changes of a system undergoing such processes are interrelated by the change in free energy, ªG, according to the equation
ªG
=
ªH - T ªS
(1)
This investigation focuses on the reaction Zn(S ) + CuSO4(aq)
Y
ZnSO4(aq) + Cu(S )
(2)
ªG will be calculated from the ªH and ªS values obtained electrochemically. The validity of Equation (1) will be tested by comparing the value of ªH obtained electrochemically with the value of ªH obtained calorimetrically for the same reaction. The electrochemical method The electrochemical method offers simple and accurate means for the determination of thermodynamic quantities. A simple electrochemical cell is constructed in a Chem-Carrou-Cell™ plate as shown in Figure 1. Cu(S )/CuSO4 (aq) || Zn(S )/ZnSO4(aq) (3)
FiªG ure 1: Set-up for measuring E versus temperature.
1
The CCLI Initiative
The overall galvanic cell reaction is Zn(S ) + Cu2+ (aq) Y Zn2+(aq) + Cu(S ) and it is essentially the same as that taking place in the calorimeter. The quantity of the electrical energy, F , produced or consumed during the electrochemical reaction is a constant measured per mole of electrons, and can be accurately measured. The free energy change, ªG , of an electrochemical reaction is related to the voltage, E, of the electrochemical cell by the equation (4)
ªG where and
= -nFE n
(5)
F
= the number of moles of electrons transferred in a redox reaction. = Faraday's