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Posted: Sun Jan 10, 2016 2:10 pm
In figure 8.18, it says that overall entropy change can be positive when the entropy of the system increases and also when the entropy of the system decreases and that in both cases it is spontaneous. How can the overall entropy change be positive in both cases if in one reaction the entropy increases and the other it decreases?
Posted: Sun Jan 10, 2016 2:22 pm
I might be mistaken but it sounds like you're using enthalpy and energy interchangeably. Remember, the enthalpy is not a measure of the energy that a system has in the same sense as the internal energy. Also, from the text it seems that when energy is transferred to a constant-pressure system as heat, the enthalpy of the system increases by that amount. Similarly, when energy leaves a system with constant pressure as heat, the enthalpy of the system decreases by that amount.
Posted: Sun Jan 10, 2016 2:38 pm
Figure 8.18 in the 6th edition is demonstrating properties of enthalpy, not entropy. Make sure you are looking at the correct edition of the textbook.