What is State function: Definition and 37 Discussions

In the thermodynamics of equilibrium, a state function, function of state, or point function is a function defined for a system relating several state variables or state quantities that depends only on the current equilibrium thermodynamic state of the system (e.g. gas, liquid, solid, crystal, or emulsion), not the path which the system took to reach its present state. A state function describes the equilibrium state of a system, thus also describing the type of system. For example, a state function could describe an atom or molecule in a gaseous, liquid, or solid form; a heterogeneous or homogeneous mixture; and the amounts of energy required to create such systems or change them into a different equilibrium state.
Internal energy, enthalpy, and entropy are examples of state quantities because they quantitatively describe an equilibrium state of a thermodynamic system, regardless of how the system arrived in that state. In contrast, mechanical work and heat are process quantities or path functions because their values depend on the specific "transition" (or "path") between two equilibrium states. Heat (in certain discrete amounts) can describe a state function such as enthalpy, but in general does not truly describe the system unless it is defined as the state function of a certain system, and thus enthalpy is described by an amount of heat. This can also apply to entropy when heat is compared to temperature. The description breaks down for quantities exhibiting hysteresis.

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  1. taimcampos92

    State function question as it applies to Biology/Physiology

    Hi everyone! Hope you all are doing great. I'm currently starting a new course mixed with Chemistry, Biochemistry, and Physics-related to Nurse anesthesia. While reading about State function a question arrived on my team. We all agreed that a State Function "is a property or characteristic of a...
  2. E

    A Ballentine on the "multicomponent state function"

    I have just finished reading Ballentine Chapter 7.2 and I am positively baffled, perhaps because Ballentine is being sloppy for the first time. I attach the discussion in Ballentine at the end of this post if it helps, though I hope my writing will be independent thereof. This question is...
  3. J

    Is the magnetic field B→. a state function and exact differential?

    is the magnetic field B→. a state function and exact differential? I argued that it's a state function, what do you guys think
  4. M

    Is the change in internal energy really a state function?

    Here is the figure: The answer is $$Q_A<Q_B$$ which I can show by calculation using the above equations. What's confusing to me is I thought that the change in internal energy was a state function. Which would mean since the initial and final points are the same, $$\Delta E_A=\Delta E_B$$ or by...
  5. Philip Koeck

    Show that entropy is a state function

    In a (reversible) Carnot cycle the entropy increase of the system during isothermal expansion at temperature TH is the same as its decrease during isothermal compression at TC. We can conclude that the entropy change of the system is zero after a complete Carnot cycle. The mentioned textbook now...
  6. Frankenstein19

    Calculate the probability that the particle's x coordinate

    Homework Statement For a 1.0 × 10-26 g particle in a box whose ends are at x = 0 and x = 2.000 Å, calculate the probability that the particle's x coordinate is between 1.6000 and 1.6001 Å if n=1 Homework Equations The Attempt at a Solution I know that since the interval between 1.6000 and...
  7. davidge

    I What does the 0-ket in this state function expression represent?

    I would like to know what the "0-ket", called vacuum state and used in the following expression, represents $$\Psi(x,t) = \int d^3x <x| \ a^{\dagger}(x) \ |0>$$ I have rewritten the expression for the case of just one ##x##. The expression above is usually presented with ##(x_1,...x_n)## (n...
  8. redtree

    I Completeness Relation: 2 Questions Answered

    Two questions regarding the completeness relation: First: I understand that the completeness relation holds for basis vectors such that ## \sum_{j=1}^{m} | n_{j} \rangle \langle n_{j} | =\mathbb{I}##. Does it also hold for unit-normalized sets of state vectors as well, where ## | \phi_{j}...
  9. G

    Why is entropy a state variable even for irreversible path?

    Hello. The entropy S is a state variable or state function as the integral of dS = dQ/T is a path-independent, provided that the path is reversible process path. However, such a path-independency of the integral breaks down when the path includes irreversible process. So, I guess we can only...
  10. grandpa2390

    Express dH(V,T) as a state function

    Homework Statement the entire problem is to show that the enthalpy as a function of volume and temperature can be expressed in the form:... I am having trouble with the first step. Homework Equations dH = TdS + VdP ##dH = (\frac{∂H}{∂S})dS + (\frac{∂H}{∂P})dP## The Attempt at a Solution I...
  11. T

    I The most general state function

    From my studying of QM, I have been learning about state functions that are supposed to describe a particular system. Now for most purposes, it seems that I have been computing the position wave function (or, through Fourier transforms, the momentum) which evolves with time. But I am just...
  12. Rohan Patil

    Thermodynamics Entropy state function?

    Entropy of any system is state dependent. I just read about thermodynamics and I got this question. I first set my system which contained my classroom, the hallway connecting my physics teacher's cabin and the classroom. Then let the entropy of the system be S when I was going to the classroom...
  13. T

    Entropy State Variable: Thermal Equilibrium Questions

    I have a few questions about entropy and path Scenario I have a closed system of Ideal Gas- Volume is Fixed , Mol Vol is fixed. At room temperature the system is in thermal equilibrium with its surroundings I then cool this system removing Q . To this system I then re-add Q until it is again in...
  14. T

    Is the difference of two state functions a state function?

    Hello everybody, For my thermodynamics test I have to tell whether or not a quantity is a state function, which is obviously not all too difficult when regarding entropy, enthalpy etc. on their own. However there are a lot of questions where it is about "H-S" or "G-H". Are these not always...
  15. G

    How Do I Determine the Change in Entropy of the System?

    Homework Statement Determine ΔSsys when 3.0 mol of an ideal gas at 25°C and 1 atm is heatedd to 125°C and expanded to 5 atm. Rationalize the sign of ΔSsys. Homework Equations State Function: dS = (dU)/T + (PdV)/T State Function for Entropy of Ideal Gas: dS = (CV,mdT)/T + (nRdV)/V Ideal gas...
  16. C

    Normalizing a State Function for an Infinite Square Well

    Homework Statement Normalize: \Psi_1 (x,t) = N_1 \cos(\frac{\pi x}{L}) e^{-\frac{iE_1t}{\hbar}} Where N_1 and E_1 are the normalization constant and energy for the ground state of a particle in an infinite square well. Homework Equations Normalization Condition: \int_\infty^\infty P(x,t)...
  17. C

    If entropy is a state function, how can it keep on increasing?

    I just have this confusion which is completely eating me up. They say entropy of a system is a state property. Then they say that for a completely isolated system, entropy either increases or remains zero depending on the process being irreversible or reversible. So, let's say for an...
  18. O

    Enthelpy and work(at constant temperature) are state function

    Enthalpy is a state function because it only depends on the initial and final state. Work is a path function because its value depend on the path. So can I say work done on a system at constant pressure is a state function ? Because the path for the work here is always the same, which is under...
  19. M

    Understanding State Functions in Thermodynamics: Consequences and Clarifications

    I am having difficulty understanding what a state function is. Yes, I know its a function of the state of the parameter, but what are the consequences of state functions? Just beginning thermodynamics and have difficulties keeping everything straight here.
  20. F

    Is Enthalpy Always Conserved in Different Expansion Paths?

    Consider gas here as idea gas. The gas expands from state 1: P1, V1 and T1 to state 2: P2, V2, and T1 using two different paths: Path A: reversible expansion at constant T Path B: irreversible expansion by releasing the gas to a vacuum to achieve V2 at adiabatic condition. Thing I...
  21. M

    Spin state function of a beam of particles in terms of eigenfunctions.

    Hi there, I apologise that I should probably know this/its a stupid question but I seem to have forgotten all physics over the holiday and so any help would be great! I have been told that there is a beam of atoms with spin quantum number 1/2 and zero orbital angular momentum, with spin +1/2...
  22. F

    Heat content as a state function?

    at 3:30 he introduces heat content to show why it can't be a state variable. he says that if q=2 is added to the cycle everytime you go around the cycle the heat content would be incremented by 2. but as heat=work shouldn't that extra 2 be lost as work and at point 1 you always have hc=5? watch...
  23. F

    Heat content as a state function?

    at 3:30 he introduces heat content to show why it can't be a state variable. he says that if q=2 is added to the cycle everytime you go around the cycle the heat content would be incremented by 2. but as heat=work shouldn't that extra 2 be lost as work and at point 1 you always have hc=5? watch...
  24. 5

    Quantum Mechanics: Choose an acceptable bound state function

    1. Which of the following is an allowed wave function for a particle in a bound state? N is a constant and α, β>0. 1) Ψ=N e-α r 2) Ψ=N(1-e-α r) 3) Ψ=Ne-α x e-β(x2+y2+z2) 4) Ψ=Non-zero constant if r<R , Ψ=0 if r>R Only one is correct. 2. What are the criteria for...
  25. A

    Clarification on thermodynamics concepts of state function, exact differential

    I would like someone to explain to me the correlations between these thermodynamics concepts: 1 State function/conservative force/reversibility 2 State function/exact differential Some functions in the phase space of a system are state function some are not. Is this simply an empirical...
  26. S

    Creation or destruction of particol in the state function

    Hi, I've studied a bit nuclear physics, and I don't get how the mathematics under the creation and destruction of particles is handled. if shrodingher equation leads a state vector in the usual way Hpsi=ih d(psi)/dt let's suppose I've N particles and psi=psi(q1...qn) so, if a new particle...
  27. I

    New state function after measurement

    Homework Statement This is an extension to problem 4.55 in Griffiths. The problem is: The electron in a hydrogen atom occupies the combined spin and position state: \lvert \psi \rangle = R_{21} \left(\sqrt{1/3} Y_1^0 \chi_+ + \sqrt{2/3} Y_1^1 \chi_-\right) a) If S_z is measured, what...
  28. C

    State Function Conditions in Isothermal, adiabatic

    In an Isothermic and reversible condition why is DH=0? (D=delta) I can understand that DU=0 but DH? but why would DH not change? DH should also =0 if it was an adiabtic and irreversible condition? since DH=dq/T -> as long as there is no heat transfer DH=0? Since it's reversible would...
  29. A

    Is Entropy a State Function for Isolated Systems?

    If we consider an isolated system in which a process occurs, then according to the clausius inequality : dS \geq \frac{dQ}{T} Since dQ = 0 , it follows that if the process occurs reversibly dS = 0 and irreversibly dS > 0. But entropy is a state function , how could this possibly be ...
  30. M

    Why entropy is a state function ?

    Why entropy is a state function ?
  31. K

    What are the other state functions and how do we determine them?

    actually i know some fundamental state function such that temperature, pressure, and volume. But it's because these are the most used. Now my problem is how to know the other state function i.e what are the conditions?
  32. E

    How do we know a state function will stay normalized?

    According to Shrodinger Equation, The state function must change with time, soI wonder how do we know that after we normalize this state function, it will stay normalized ? Thanks
  33. J

    What is the Frequency of a State Function Describing a Proton?

    I have this state function that I've gotten to the form: \Psi = A*\exp[iE_1 t/h] + B*\exp[4iE_1 t/h] where A and B are functions of x. I know the energy. The h's are h-bars. The state function is suppose to describe a proton and I'm asked to find the frequency. My first thought is...
  34. A

    Why U is a State Function if W(adiabatic) Does Not Depend on State?

    if work is not a state function and internal energy is a state function, then why does w(adiabatic)=U is a state function?
  35. A

    Vanishing of a cyclic integral the property of a state function?

    Why is the vanishing of a cyclic integral the property of a state function?
  36. M

    Do a state function be multu-valued function

    Does a state function be multi-valued function A thermodynamic state function should be single valued function of independent varibles. In case of steamtables of pure water, there is same entahlpy (U=2000 kJ/kg) at temperature T1=700K and pressure P1=63.458 MPa, and at T2=700K and P2=456.356...
  37. T

    Is air density a state function?

    I know there is a simple equation using absolute pressure and absolute temperature that predicts the density air in our atmosphere. This is commonly used in weather forcasting. My question is that if air undergoes a process of compression, cooling, etc...ending up at a pressure P and a...