Equilibrium Definition and 1000 Threads

Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermodynamic equilibrium there are no net macroscopic flows of matter or of energy, either within a system or between systems.
In a system that is in its own state of internal thermodynamic equilibrium, no macroscopic change occurs.
Systems in mutual thermodynamic equilibrium are simultaneously in mutual thermal, mechanical, chemical, and radiative equilibria. Systems can be in one kind of mutual equilibrium, though not in others. In thermodynamic equilibrium, all kinds of equilibrium hold at once and indefinitely, until disturbed by a thermodynamic operation. In a macroscopic equilibrium, perfectly or almost perfectly balanced microscopic exchanges occur; this is the physical explanation of the notion of macroscopic equilibrium.
A thermodynamic system in a state of internal thermodynamic equilibrium has a spatially uniform temperature. Its intensive properties, other than temperature, may be driven to spatial inhomogeneity by an unchanging long-range force field imposed on it by its surroundings.
In systems that are at a state of non-equilibrium there are, by contrast, net flows of matter or energy. If such changes can be triggered to occur in a system in which they are not already occurring, the system is said to be in a meta-stable equilibrium.
Though not a widely named "law," it is an axiom of thermodynamics that there exist states of thermodynamic equilibrium. The second law of thermodynamics states that when a body of material starts from an equilibrium state, in which, portions of it are held at different states by more or less permeable or impermeable partitions, and a thermodynamic operation removes or makes the partitions more permeable and it is isolated, then it spontaneously reaches its own, new state of internal thermodynamic equilibrium, and this is accompanied by an increase in the sum of the entropies of the portions.

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  1. J

    Static Equilibrium and tension of cables

    Homework Statement A 30Kg neon sign is suspended by two cables, as shown. Three neighbourhood cats (5.0 Kg each) find the sign a comfortable place. Calculate the tension in each cable with the cats are in the positions shown. Homework Equations xCM = m1x1 + m2x2 ...
  2. J

    Static Equilibrium with a beam and cable

    Homework Statement A uniform vertical beam of mass 40kg is acted on by a horizontal force of 520N at its top and is held, in the vertical position, by a cable as shown in the attached picture. a) Calculate the tension in the cable b) Determine the reaction forces acting on the beam by the...
  3. O

    MHB Determining Stability of Equilibrium Point for x'=y-x3-xy2, y'=-x-x2y-y3

    i have this system x'=y-x3-xy2 y'=-x-x2y-y3 i worked it out and found the equilibrium point to be 0. how do i determine whether it is stable, assymp stable or not stable
  4. S

    MHB Equilibrium points and lipschitz functions

    Given a function Hn-Hn is localy lip on its domain and f(p)=0 for some p an element of D if x is a solution of the system x' =f(x) on interval I and x(s) not equal to p for some s in I. how can i show that x(t) is not equal to p for all t in I
  5. F

    Equilibrium temperature of a mixture

    Homework Statement Homework Equations Q = m c \Delta T \\ Q = m L_v \\ Q_{in} = Q_{out} The Attempt at a Solution m_s c_s (100 - 8) + m_s L_v = m_s c_s (100 - T) + m_m c_s (T) \\ 5778.06 + 33900 = 5778.06 - 62.805 T + 418.7 T \\ 33900 = 355.895 T \\ ∴ T = 95.25°C Answer should...
  6. T

    What is the partial pressure of ammonia at equilibrium?

    Homework Statement Ammonia gas decomposes to nitrogen and hydrogen spontaneously with an equilibrium constant, Kp = 5.9 x 109. Calculate the partial pressure of ammonia at equilibrium given that the partial pressure of nitrogen and hydrogen are both 2.7 atm initially. [Hint: If you need...
  7. K

    Finding the charge on two balls in equilibrium

    Two balls, each of mass 0.50g are each suspendedd from an insulating thread 1.0m long. The upper ends of the threads are attached to the same point. When the balls are equally charged they repel each other and are in equilibrium when they are 30cm apart. Find the charge on the two balls. F =...
  8. B

    Two Objects In Thermal Equilibrium

    Hello everyone, I was wondering, is there any way of calculating the time it takes for two objects in thermal contact to come to thermal equilibrium?
  9. K

    What are the Equilibrium Conditions for a 3D Rigid Body with Applied Forces?

    Homework Statement The rod assembly shown has a ball-and-socket joint at A and a smooth journal bearing at C. The forces F1=600N , F2=410N , F3=460N , and F4=950N are applied as shown in the figure. The geometry of the rod assembly is given as a=0.900m , b=0.650m , and c=0.800m...
  10. G

    Can equilibrium rate constant has unit of [time^-1]?

    Hi all, I am having a homework problem that is statement really bothers me and I think it might be a typo. It goes in the following: Homework Statement A is a short life unstable state and it is in equilibrium with B and C. A\LeftrightarrowB A\LeftrightarrowC The equilibrium rate constants...
  11. S

    What Was the Initial Quantity of Hydrogen Fluoride in the Reaction Jar?

    Homework Statement Keq at a given temperature is 4 2 HF (g) <--> H2 (g) + F2 (g) A 1 Litre jar contains 0.045 moles of fluorine at equilibrium. What was the initial quantity of hydrogen fluoride in the reaction jar? 2. The attempt at a solution I set the initial concentration...
  12. S

    Factors Affecting Equilibrium Questions.

    Homework Statement 1) Equilibrium is achieved in a closed system where metallic Mg can react with HCl(aq) according to the following net chemical equation: Mg(s) + 2 H+(aq) <--> Mg+2(aq)+ H2(aq) A sodium hydroxide, NaOH(s), pellet is added to this system. What happens to the concentration...
  13. E

    Calculate total energy from potential at equilibrium point

    Homework Statement A block of mass 0.25 kg is connected to a spring with spring constant 35 N/m. The block is oscillating on a frictionless horizontal surface. Its speed as it passes through its equilibrium position is 1.04 m/s. What's the total energy of the system?2. The attempt at a...
  14. J

    Changing equilibrium point in damped simple harmonic motion

    Hi I have a damped simple harmonic motion model and I am altering the input force along with spring constant and damping constant. I can change the damping and spring constant to allow it to oscillate for few seconds before it stops at 0. What parameters do I need to change to alter the...
  15. U

    Find the equilibrium position of this piston

    Homework Statement A portion of helium gas in a vertical cylindrical container is in thermodynamic equilibrium with the surroundings. The gas is confined by a movable heavy piston. The piston is slowly elevated a distance H from its equilibrium position and then kept in the elevated position...
  16. Entanglement

    Concentration of solids in equilibrium

    It's known that the concentration of solids don't affect the rate of the reaction since it's concentration is constant, I know that when the number of moles of a solid is increased the volume also increases the same so the concentration remains constant so the rate doesn't change, but when the...
  17. Entanglement

    The volume of a solution at equilibrium

    Say that we have a salt solution does the volume of the solution change after when the salt is ionized and equilibrium is achieved ??
  18. A

    Tensions Equilibrium: Finding Unit Vectors

    Homework Statement see picHomework Equations The Attempt at a Solution Ive worked out T1 which is T1=F1(-4i-5j-10k/11.8743) = T1(-0.337i-0.421j-0.842k) and T2=F2(-4i-5j-10k/11.8743) =T2(0.337i-0.421j-0.842k) and the next step is to find the unit vector of force M = 20kn but how do i work out...
  19. M

    What is the Maximum Angle for a Crutch to Not Slip on the Ground?

    Hi All- Hope you can help me :| Homework Statement The person in the drawing is standing on crutches. Assume that the force exerted on each crutch by the ground is directed along the crutch, as the force vectors in the drawing indicate. If the coefficient of static friction between a crutch...
  20. M

    Thermal Equilibrium With Insulated Liquid And Gas Containers

    Homework Statement A beaker with a metal bottom is filled with 20g of water at 20∘C. It is brought into good thermal contact with a 4000 cm^3 container holding 0.40mol of a monatomic gas at 10atm pressure. Both containers are well insulated from their surroundings. What is the gas pressure...
  21. M

    Visualizing Forces in equilibrium

    Hi, I am studying for the MCATs, and currently going through physics. Sadly its my weakest area :( For the last three weeks I am stuck on conservative/non-conservative forces. The problem seems to be that I keep missing important associated forces on a system. For example: I got stuck...
  22. S

    Can Aeration Change the Equilibrium of Gases in Water?

    Hi, first time poster. Here's the scenario. In a given vessel containing a given amount of water at a given temp, gases from the air will reach equilibrium with those dissolved in the water contained in the vessel. Now suppose live plants are added to the water. During the day, photosynthesis...
  23. D

    How is Kp(T) Derived for Dissociation of H2O at High Temperatures?

    Hello I'm solving previous exams and there is this exercise that appears in almost every exam : Homework Statement Suppose v moles of a gas H2O are enclosed in a constant volume V at a low temperature so the gas is in aN undissociated state. At highest temperatureS, H2O molecules are...
  24. S

    A Question about Torque Used for Static Equilibrium

    Homework Statement A diving board 3.00m long is held down at the left end and is supported underneath at a point 1.00m to the right of the hold. A diver weighing 500N stands at the other end. The diving board is of uniform cross section and weighs 280N. Find (a) the force at the support...
  25. Entanglement

    Understanding Equilibrium Calculations: Debunking Misconceptions

    My solution for this question is Kc=1/10 As the ratio of both forward and backward rate constants never changes unless the temperature changes. My teacher told me that the answer is 1/100 because the reaction's products and reactants are doubled, that seems senseless to me, I don't want to...
  26. nicolauslamsiu

    Equilibrium Position: How Water Affects System

    I want to ask how will the equilibrium position of the system change if water is added to the system?
  27. BrainMan

    Objects in equilibrium beam problem

    Problem: A uniform beam of length 4 m and mass 10 kg, connected to the side of a building by a pivot hinge, supports a 20-kg light fixture,as shown in figure 4.43. Determine the tension in the wire and the components of the reaction force at the pivot. Equations: sum of forces =0 Sum of...
  28. M

    Torque Equilibrium to find center of mass.

    Homework Statement 1. A non-uniform beam with a mass of 85kg has a length of 6.2m and is attached to a wall and supported at an angle of 28 degrees from the wall by a horizontal rope which is attached to the wall above the beam . The tension in the rope is found to be 310N. How far from the...
  29. BrainMan

    Objects in equilibrium hinged platform with cable problem

    Homework Statement A hinged platform flagpole weighing 500 Newtons is supported in the horizontal position by a cable as shown in figure 4.35. Find the tension in the cable and the horizontal and vertical forces at the hinge. Angle ø = 30°Homework Equations ∑F=0 ∑T=0 T= F* the lever armThe...
  30. M

    Markov equilibrium probabilities

    Homework Statement A Markov process with 4 states evolves in unit time steps with a transition probability matrix given by P = |0.5 0 0.3 0.2| |0.1 0.4 0.2 0.3| | 0 0.4 0.4 0.2| |0.1 0.1 0.1 0.7| Find the equilibrium probabilities for this system. What is the most likely state...
  31. C

    What is the Equilibrium Shape of a String Suspended Between Two Points?

    Homework Statement An inextensible string of length ##\ell##, whose mass per unit length is ##\rho## is hung between two points at the same height a distance ##d## apart (##d < \ell)##. Using the Euler-Lagrange equations and the first integrals, find the shape of the string when it is in...
  32. BrainMan

    How Far Can a Person Walk on a Plank Before It Tips?

    The problem is a uniform plank of length 6 m and mass 30 kg rests horizontally on a scaffold, with 1.5 m of the plank hanging over one end of the scaffold. How far can a 70 kg person walk on the overhanging part of the plank before it tips? Relevant equations Sum of all the forces = 0 Sum of...
  33. Y

    Decomposition of N2O5 Entropy Equilibrium

    Please see attached picture. I need verification of my answers. I unfortunately found these problems on an old book with no answer. I would really appreciate it. (a) Ok. For this one, I am really not sure. PLEASE help. I get a very complicated formula. (1+x)(x^4)/(1-x)^2=Kp. Now, this...
  34. D

    Calculating pH of Buffered Solutions: Do You Need a Ka/Kb Value?

    Hello, So as the end of the year comes to an end, AP Chemistry is getting increasingly more difficult to the point where I don't understand anymore. In our homework there is a questions asking to calculate the pH of a buffered solution. The only information it gives you is the chemical formula...
  35. V

    Show that the total weight w of an assembly in thermal equilibrium is

    Homework Statement Show that the total weight w of an assembly in thermal equilibrium is a maximum. Homework Equations S= k ln W? dS = dQ/ T ? S is maximize when thermal equilibrium is reached. The Attempt at a Solution First of all, i don't know what does "total weight w" means...
  36. A

    What is the required h for equilibrium in a body with two center of masses?

    Homework Statement problem attached Homework Equations The Attempt at a Solution i had no problem with part i and ii , iii on the other hand, i simply don't know what i should do , i figured out that the required h will be the one making the center of mass of the whole body on...
  37. M

    Ice Cubes and Drink Equilibrium

    Homework Statement In an attempt to quickly make iced tea, three 50 g ice cubes with a temperature of -10 C are added to 250 g of tea with a temperature of 50 C. After a short time, the system reaches equilibrium. Ice has a specific heat capacity of 0.48 kcal/kg/K and the latent heat of...
  38. D

    Equilibrium Points of a System given its Lagrangian

    Given a system's Lagrangian, How can we calculate the equilibrium points corresponding to the system? also how can we determine if that's a stable equilibrium?
  39. S

    MHB Is a Limit Point Always an Equilibrium in Differential Equations?

    Say x is a solution of the DE x’=f(x) and f is a continuous derivative on its domain, if lim┬(t→͚inifinity⁡〖x(t)〗=p then p is equilibriumhow can I show that this is true
  40. A

    Equilibrium and tension in elastic strings

    Homework Statement problem attached Homework Equations The Attempt at a Solution well, there is pretty much nothing i can write here, i couldn't solve it because this is the first time i face a problem like that , i have some problems understanding it though 1-if we considered the...
  41. E

    Doubt in equilibrium of rigid body

    Hello there! I am currently studying the equilibrium of rigid body and encountering a doubt. Now, in their explanation of reaction forces by a roller or a rocker or a smooth surface, they generalize it as in the preceding examples prevent the translation of a beam for example in ONE direction...
  42. M

    Equilibrium of a Rigid Body: Finding Unknown Mass on a Lever

    Homework Statement Find the unknown mass on a lever (see-saw). I have three masses. To the right of the fulcrum, the mass is 166 g and it is 25.15 cm from the fulcrum. There are two masses to the left. One is 166 g and is 16.95 cm from the fulcrum. The unknown mass is 3.33 cm from the fulcrum...
  43. S

    Why didn't we need to calculate the x-component in our pulley system lab?

    We had a lab 2 weeks ago that dealt with predicting the "known unknown" masses (we know it's 250g and we have to experiment to try and get to 250g as close as possible) within a pulley system. All three trials we had for part 1, where the known unknown was placed in the middle, we only...
  44. M

    What are the pin reactions at A and D?

    Homework Statement The two couples act at the midpoints of bars AB and BD. Determine the magnitudes of the pin reactions at A and D. Neglect the Weights of the members. [See Attachments for Figure] Homework Equations Sum Moment Along A & D = 0 Sum of Forces along X-axis Sum forces along...
  45. Entanglement

    Equilibrium Constant: H2+O2->H2O

    H2+1/2 O2 ---------> H20 If the equation is multiplied by 2 Will the equilibrium constant change or remain constant ?
  46. L

    Hydrostatic Equilibrium in a Star

    Homework Statement Hello. In my homework I was given to find a mistake in a derivation of hydrostatic equilibrium of a star. In contrast to "regular" derivation, where a cylindrical segment is chosen, in HW a segment of sphere is used: Homework Equations Derivation is given as following: a...
  47. R

    Using Lagrange to solve rotating parabolic motion and equilibrium

    Homework Statement Consider a bead of mass m sliding without friction on a wire that is bent in the shape of a parabola and is being spun with constant angular velocity w about its vertical axis. Use cylindrical polar coordinates and let the equation of the parabola be z = kp2. Write down the...
  48. Feodalherren

    Thermal Equilibrium of a system

    Homework Statement A combination of .25kg of H2O at 20C, .4kg of Al at 26C and .1kg of Cu at 100C is mixed in an insulated container and allowed to come to thermal equilibrium. Ignore any energy transfer to or from the container and determine the final T of the mixture. Homework Equations...
  49. W

    What is the Mass of the Block Placed on a Stiff Board in Static Equilibrium?

    Homework Statement Two supports, made of the same material and initially of equal length, are 2.0m apart. A stiff board with a length of 4.0m and a mass of 10 kg is placed on the supports, with one support at the left end and the other at the midpoint. A block is placed on the board a...
  50. O

    Conductors in Electrostatic Equilibrium

    A long straight metal rod has a radius of 5 cm and a charge per unit length of 30 nC/m. Find the electric field x cm away where distance is perpendicular to the rod.The solution to this uses ## \int E\cdot dA = \dfrac{q_{encl}}{\epsilon_0}##. My question is, why can you use this? I thought...
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