You are watching: Why is work not a state function
This is the extract from Halliday & Resnick.
My chem book writes:
Heat & work-related are the creates of power in transit. They show up just once tright here occurs any readjust in the state of system and also the surroundings. They don"t exist before or after the change of the state.
So, heat energy is dependent on the course or the way the system alters, right? So, are they saying, for one course connecting two states, even more warmth energy deserve to be liberated while for one more course, much less warmth is released? How? For the very same two claims, how have the right to tright here be a various amount of warmth power liberated? Is there any intuitive example to understand this?
Improve this question
edited Jun 7 "18 at 9:12
Thomas Lee Abshier ND
80411 gold badge99 silver badges1414 bronze badges
asked Nov 17 "14 at 12:24
Add a comment |
5 Answers 5
Active Oldest Votes
Think of it like this. When you have actually an object of mass $m$ which is organized a height $h$ above some referral allude, you think of it as having actually potential power (considering just gravitational interactions) $U= m g h$, and gravity will certainly exert an amount of work $W_g = m g h$ on the object. When you drop the object, it shall loss in the direction of the ground, in the direction of “equilibrium”, so to sheight. You do not sheight of the amount of “work” that the mass has as soon as at its original height, nor of the amount of “work” shed, but of its power (loved one to a referral point) at any offered state, $U$. In addition, we say that this potential power is a state feature because it relies only on the initial and also last heights of the mass in question.
See more: Why Don’T Adult Echinoderms Exhibit True Radial Symmetry? ? Echinoderms Flashcards
In the exact same means, one does not concern his or her self via the amount of “heat” that an object has, because it is merely a term provided to represent the amount of moved energy in between systems as they relocate in and also out of equilibria. We sheight of thermal power, inner power, totally free energies and also such that are state attributes of the mechanism - in exactly the same method that the gravitational potential power $U$ remained in the mechanical analogue to this thermodynamical instance. In the exact same way, we say that the thermal power of the mechanism is a state feature insomuch that it generally counts (even more or less) on the initial and final temperatures and thermodynamic quantities of the mass in question.
Edit: I’ve reread your question and also I want to make an additional allude to clear points up. Yes, indeed, different routes have the right to result in different amounts of warmth transfer - the first law of thermodynamics states:
$delta E = Q + W$,wherein $Q$ is the amount of warmth circulation into the device, $W$ is the work-related done onto the mechanism, and also $delta E$ is the total state internal energy change of the device. One have the right to view that one can input say, 100 J of heat and execute no work-related on a system to cause a net readjust $delta E$ of 100 J, and also in the same way, one can divide that $100 J$ amongst $W$ and $Q$ to get the very same result.
The intuition is as follows. Imagine you have a jar of gas. You ca rise the temperature (and so imcomponent a positive $delta E$) by including $100 J$ of heat, or you may compress it by doing $100 J$ of job-related to gain the exact same result. I hope that clears points up!