Electrochemical Reaction Lab Report

In this laboratory voltmeters where utilized to take reading of three different electrochemical reactions: Pb/Zn, Pb/Cu, and Zn/Cu. A salt bridge was placed between two reactions containing metal strips in separate aq solutions. The salt bridge was placed in order to balance the reaction. The voltage measurements for Pb/Zn, Pb/Cu, and Zn/Cu where .595 V, .479 V, and 1.072 V accordingly. The values obtained where then used to determine the voltage value for the reduction half. The resulting cell potential for Cu, Pb and Zn were calculated to be .34 V, -.139V, and -.732 V. looking at this data leads to determine that the experiment was successful up to this point. Once the experiment proceeded to the second part errors began to pile up at a faster rate.
The expected result would be as temperature decreases so does the voltage. In terms of Gibbs free energy this makes sense because as it becomes more negative, electron movement should decrease as well. In this experiment however there seems to be an initial spike instead of decrease, which while it does occur towards the end the results seem to be wildly inconsistent. This data yields a positive slope (3.31 J), this should not be the case because in a Gibbs free energy versus temperature graph the slope should be negative.
The inconsistency of the data where catastrophic. Everything that was calculated using the slope such as the entropy were also incorrect. When the entropy change when compared to the enthalpy both have the same result negative. This would indicate the reaction to be spontaneous only at the lower temperatures. This is wrong because it should be spontaneous at all temperatures. This then affected the calculations of Gibbs free energy leading to incorrect calculations and a less than stellar end to the