# Equilibirium Definition and 64 Discussions

In thermodynamics and chemical engineering, the vapor–liquid equilibrium (VLE) describes the distribution of a chemical species between the vapor phase and a liquid phase.
The concentration of a vapor in contact with its liquid, especially at equilibrium, is often expressed in terms of vapor pressure, which will be a partial pressure (a part of the total gas pressure) if any other gas(es) are present with the vapor. The equilibrium vapor pressure of a liquid is in general strongly dependent on temperature. At vapor–liquid equilibrium, a liquid with individual components in certain concentrations will have an equilibrium vapor in which the concentrations or partial pressures of the vapor components have certain values depending on all of the liquid component concentrations and the temperature. The converse is also true: if a vapor with components at certain concentrations or partial pressures is in vapor–liquid equilibrium with its liquid, then the component concentrations in the liquid will be determined dependent on the vapor concentrations and on the temperature. The equilibrium concentration of each component in the liquid phase is often different from its concentration (or vapor pressure) in the vapor phase, but there is a relationship. The VLE concentration data can be determined experimentally, approximated with the help of theories such as Raoult's law, Dalton's law, and Henry's law.
Such vapor–liquid equilibrium information is useful in designing columns for distillation, especially fractional distillation, which is a particular specialty of chemical engineers. Distillation is a process used to separate or partially separate components in a mixture by boiling (vaporization) followed by condensation. Distillation takes advantage of differences in concentrations of components in the liquid and vapor phases.
In mixtures containing two or more components, the concentrations of each component are often expressed as mole fractions. The mole fraction of a given component of a mixture in a particular phase (either the vapor or the liquid phase) is the number of moles of that component in that phase divided by the total number of moles of all components in that phase.
Binary mixtures are those having two components. Three-component mixtures are called ternary mixtures. There can be VLE data for mixtures with even more components, but such data is often hard to show graphically. VLE data is a function of the total pressure, such as 1 atm or at the pressure the process is conducted at.
When a temperature is reached such that the sum of the equilibrium vapor pressures of the liquid components becomes equal to the total pressure of the system (it is otherwise smaller), then vapor bubbles generated from the liquid begin to displace the gas that was maintaining the overall pressure, and the mixture is said to boil. This temperature is called the boiling point of the liquid mixture at the given pressure. (It is assumed that the total pressure is held steady by adjusting the total volume of the system to accommodate the specific volume changes that accompany boiling.) The boiling point at an overall pressure of 1 atm is called the normal boiling point of the liquid mixture.

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1. ### Medical Question about reactions in biochemistry

we assume that we have an exergonic reaction , a substrate going to a product , is the negative ΔG′° the principal reason that the equilibrium favors the product (there is more product than substrate at equilibrium )?, or it is not and that depends on other factors? , thanks .

40. ### Change in Gibbs free energy at equillibrium

I understand that the change in Gibbs Free Energy at equillibrium is 0 and this leads to the equation -deltaH=TdeltaS. My questions here is that if a reaction is at equillibrium, how can there be any change in enthalpy or entropy at all? Why wouldn't these terms be 0?
41. ### I am sure I am doing this Acid/Base problem wrong

What is the pH of a solution made from 34.6 ml if 3.45*10^-4 M of H2SO4 added to 41.7 ml of 4.56*10^-4 M of Al(OH)3? I know how to find H+ and OH- and pH I also know how to use x mol / L, but I cannot get them to click together. Everyone keeps telling me to use RICE but my professor never...
42. ### How to find if equilibrium points of a force is un/stable?

Homework Statement U = Ax2 - Bx3 Homework Equations du/dx = 2Ax - 3Bx2 The Attempt at a Solution If I was given a potential energy function U = Ax2 - Bx3 and am asked to find: 1) The expression for the force as a function of x. 2) The equilibrium points and determine if are they stable or...
43. ### Force of tabletop

A ball of mass 15.47kg rests on a table of height 0.73m. The tabletop is rectangular with a mass of 12.11kg, supported by 4 thin legs. The width of it is 134.0cm and length of 63.7cm. If the ball touches the tabletop at point (67.0cm, 16.4cm) relative to corner 1, what is the force the tabletop...
44. ### Find the displacement from the equilibrium position

Homework Statement Find the displacement from the equilibrium position of the particle that is in the distance x=£/12 from the wave source, for the moment t=T/4. The amplitude of the wave is A=0.2 m Homework Equations x=A*cos(wt)=A*cos2*pi/T* t The Attempt at a Solution x=£/12...
45. ### Determining equilibrium position between two springs

Homework Statement see attachment ***indicates correct answer Homework Equations F=ks The Attempt at a Solution I do not understand how this works, and I haven't been able to find any examples of this.
46. ### Equilibrium constant value.

When does the value of the "Equilibrium Constant (K)" equal one ? and what does that mean ?
47. ### Swinging, equilibrium, kinetic energy problem

Homework Statement This is a more than one part question that depends on answers from the previous parts, which I have so I will not rewrite those questions. I will write the question I am facing difficulty with: Answers from previous parts: Length = 1.95 m (From top of chains to center, its...
48. ### Mass hangs in equilibrium on a spring (oscillation)(MCQ)

Homework Statement A mass M hangs in equilibrium on a spring. M is made to oscillate about the equilibrium position by pulling it down 10 cm and releasing it. The time for M to travel back to the equilibrium position for the first time is 0.5s. Which line, A to D, is correct for these...
49. ### Minimum force to make box slide down slope

Homework Statement If m=5.0kg, φ=30◦ and μs =0.87, what is the minimum force needed to make the box slide down the slope? [/B] Homework Equations force of status friction is less than or equal to the normal force multiplied by the coefficient of static friction F,normal=mgcosφ The image...
50. ### Explaining The Non-Reaction Of An Iron Nail With Equilibrium

The question asks: Recall that you observed very little corrosion occurring on the iron nail immersed in NaOH(aq) solution. This observation is difficult to explain from an electrochemistry perspective since electrochemistry principles predict a spontaneous reaction that should cause...