Why is enthalpy a state function

If we consider a pure substance, with molar heat capacity c P , we can write. The relation of enthalpy H to internal energy U is central to its defintion as a thermodynamic function. Specifically, enthalpy of a system is defined as. The enthalpy changes for chemical reactions occuring in aqueous solution under atmospheric pressure can generally be conveniently measured. Furthermore, as biochemical processes mostly occur under conditions of constant pressure, the enthalpy function is better suited than internal energy to biochemical applications.

In other words, there can be thermal energy exchange without a temperature change. Let us analyze the energetics of a simple phase change example. Let us assume that the surroundings are slightly warmer, so that spontaneous energy transfer occurs. Thermochemical equations are the balanced chemical equations for a process or reaction together with one or more quantities representing the accompanying changes in the thermodynamic functions per mole for the reaction as written.

For example, for the physical process of ice melting represented above, we would write. When writing thermochemical equations for chemical reactions, the preceding example should remind us that it is crucial to specify the physical state of all reactants and products.

For example, under standard conditions. Lactic acid Correct! While numerically correct, your answer has the wrong sign. Try again. That is incorrect. Please try again. Why is the enthalpy of formation of oxygen zero? Why can enthalpy not be measured directly? How does pressure affect enthalpy? How does enthalpy relate to internal energy? How does entropy effect enthalpy? See all questions in Enthalpy. Introduction Whenever compounds or chemical reactions are discussed, one of the first things mentioned is the state of the specific molecule or compound.

Mathematics of State Functions Another way to think of state functions is as integrals. State Functions vs. Path Functions State functions are defined by comparing them to path functions. Table 1: Summary of differences between state and path functions State Function Path Function Independent of path taken to establish property or value. Dependent on path taken to establish property or value. Can integrate using final and initial values. Need multiple integrals and limits of integration in order to integrate.

Multiple steps result in same value. Multiple steps result in different value. Based on established state of system temperature, pressure, amount, and identity of system. Based on how state of system was established. Normally represented by an uppercase letter. Analogy The main point to remember when trying to identify a state function is to determine whether the path taken to reach the function affects the value.

Problems In terms of what we have discussed in this module, is going from the 1st floor of Sproul hall, to the 9th floor of Sproul hall, the same thing as going from the 1st floor of Sproul hall, to the 3rd floor, to the 5th floor, to the 9th floor of Sproul hall? Is temperature a state function? Is volume a state function? Solutions Yes, because the question describes a state function. Your position is dependent only on the final and initial position, which are respectively 9th floor of Sproul and 1st floor of Sproul, and not on the path or way taken to get there.