Hi,
I don't understand why heat is not a state property, but heat at constant pressure (enthalpy) is a state property. How to explain this difference?
heat vs enthalpy
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Re: heat vs enthalpy
Enthalpy is the net change in heat of a reaction within a system. State properties account for properties within a system. Heat (and work) account for the transfer of energy into and out of a system.
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Re: heat vs enthalpy
I think because you cannot calculate the change in heat using "change in heat=final heat-initial heat" unless the pressure is held constant.
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Re: heat vs enthalpy
A state property is something that describes an object's state independent of the path taken to obtain that state. Enthalpy is a state function because it does not depend on the path taken, as the change in enthalpy is enthalpy final - enthalpy initial. However, heat depends on the path taken to get from the initial to the final heat values, so heat is not considered a state function unless it is under conditions of constant pressure, in which it becomes enthalpy.
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Re: heat vs enthalpy
Enthalpy is a state function because it is simply how much heat is released or absorbed at a constant pressure. This wont change no matter the transition. On the other hand, heat is not a state function because it depends on the path taken.
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Re: heat vs enthalpy
Hi! Heat is not a state property because it is dependent on the pathway it took, so we cannot just draw conclusions based on the initial and final values of heat. But, we can use these values to find the enthalpy of a chemical reaction, which is the amount of heat absorbed or released by a reaction at a constant pressure. Enthalpy is a state property because we just need to know the final and initial heat values to calculate it, as it is independent of the pathway of the reaction. Heat on the other hand can vary between reactions, so we need to know the exact details of the pathway it took to calculate the heat during a certain time of a reaction. I hope this helps!
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