State Properties

[Charly Ng 1K]

In the Friday lecture, Professor Lavelle says that since enthalpy is a state function, it must be additive. I'm not really sure I understand this. What is the relationship between being a state function and its ability to be additive?

[Aliza Hacking 1A]

hi! so a state property basically means that it is only the final value or difference that matters, rather than "how you got there." in other words, if two people take two different paths from point A to point B, when considering a state function, you would only care that their initial and final destinations are the same distance apart (since the points themselves are the same), even if person A took a longer route than person B to reach the same point. Since with enthalpy you only care about the ultimate numerical quantity, rather than the make up of that quantity (which bonds created which percentages of the enthalpy, etc) it is additive. it's honestly more of a definition you memorize than anything else I think :) sorry if this is confusing

[Jaden Nguyen 2A]

As Aliza said, being a state property means you can add things together without caring about how you got there because only the final number matters. This is going to make sense when you start doing calculations with Hess' Law because this law ONLY works because enthalpy is a state function. Hess' Law lets you add enthalpies of several reactions together because as a state property, the only thing that matter is that final number you see in your calculator. Hopes this helps!

[Hannah Chang 1F]

Similar to the example Aliza gave, one way to more concretely conceptualize this idea of state functions and their ability to be additive is by thinking about distance vs. displacement. Displacement doesn't depend on the path the object takes to get from point A to point B; thus, to find the displacement of an object we can simply just subtract the position of the object at point B by the position of the object at point A (or, to put in terms of addition, just add up how far the two points are from each other). However, distance does depend on the path taken, for a person who takes a longer path to get from point A to point B will have a longer distance than someone who takes a shorter path to get from point A to point B. Consequently, to calculate distance, we can't just subtract the position of point B by the position of point A, because distance depends on the path taken.

[Adithi Ayyala 2G]

Hello! Essentially, as we add up these various values, our final result for Hess's law is the only value we are actually interested in, and therefore, we refer to this as additive.

[Jonathan Liu 2I]

The state value means that the path does not matter. This means that we can add the values together and not take into account of how the values were obtained.

[KyleNagasawaDisc3C_Chem 14B2022W_]

Hey Charly,

Path-dependent and state-dependent properties are two very commonly used terms in physical chemistry describing the nature of properties associated with a system. A state describes the current status of a system.

Let's use the example of the Ideal Gas Law. The Pressure of a Gas can be defined as the state variables of volume, moles, and temperature, such that P(V,R,T) is a state-dependent property. Something like work (in a non-conservative vector field) is a property that depends on the path taken to change between states and its initial state. In general cases, state properties can be defined in terms of simple arithmetic with a current state variable set or between state variable sets, while path properties tend to involve integrating over a path.

[Crystal Ma 2J]

hi, state properties are additive since they are values determined by the current state, meaning that the process or path taken to obtain that state does not matter!