Problem: Consider the systems shown in the following figure. In one case the battery becomes completely discharged by running the current through a heater, and in the other by running a fan. Both processes occur at constant pressure. In both cases the change in state of the system is the same: The battery goes from being fully charged to being fully discharged. Yet in one case the heat evolved is large, and in the other it is small.What can you say about the relationship between enthalpy change and q in this case, as compared with others that we have considered?

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at constant pressure, ΔH = q


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Problem Details
Consider the systems shown in the following figure. In one case the battery becomes completely discharged by running the current through a heater, and in the other by running a fan. Both processes occur at constant pressure. In both cases the change in state of the system is the same: The battery goes from being fully charged to being fully discharged. Yet in one case the heat evolved is large, and in the other it is small.
a) Energy lost only as heat.  A diagram shows a battery connected to a resistor.  Initially, the battery is fully charged, but as energy is lost via heat, the battery is discharged.  The total energy lost by the battery is delta-E. b) Energy lost as both heat and work. A diagram shows a battery connected to a fan.  Initially, the battery is fully charged, but as energy is lost via heat and work, the battery is discharged.  The total energy lost by the battery, through both heat and work, is delta-E.
What can you say about the relationship between enthalpy change and q in this case, as compared with others that we have considered?

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