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Heat isn't a state function because the amount of energy transferred as heat depends on how the change in energy occurs. On the other hand, enthalpy is a state function because no matter how the energy change occurs, it only depends on the state of the system.
Enthalpy is a state function because when calculating the value it depends on the state the system is currently in. You only take into account the final value minus the initial value. Meaning that the path it took to get from the initial to the final value is not taken into account in the equation. Heat is not a state function because the energy transferred is the amount that goes in or out of a system. In this situation, the path that the energy takes matters. Energy can go in the system (+) or energy can leave the system (-).
Dr. Lavelle gave an example in class with the heating curve for water. The graph showed heat absorbed on the x-axis and temperature on the y-axis. As heat constantly increased, the temperature remained constant and only increased once certain thresholds were reached (melting or boiling points). The temperature is a state property in this case since it only depended on the initial and final state of the system to change. Heat, on the other hand, is not a state property because it was constantly supplied to the system
005384106 wrote:What is the difference between boiling an melting point?
Boiling point is the temperature a substance has to reach in order for it to boil (liquid to gas), and the melting point is the temperature a substance has to reach in order for it to melt (with solid items since they are melting).
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