Questions tagged [equilibrium]
The state in which both reactants and products are present at concentrations which have no further tendency to change with time.
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Is a negative pH level physically possible?
A friend of mine was looking over the definition of pH and was wondering if it is possible to have a negative pH. From the equation below, it certainly seems mathematically possible—if you have a $1.1$...
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What is the difference between ∆G and ∆G°?
In Brady's Molecular Nature of Matter, I read that $\Delta_\mathrm{r} G^{\circ}$ is $\Delta_\mathrm{r} G$ at $25~^\circ\mathrm{C}$. But later, it gives a value for $\Delta_\mathrm{r} G^\circ$ at ...
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Gibbs free energy-minimum or zero?
A reaction proceeds towards the direction of lesser Gibbs free energy (at constant $T$ (temperature) and $P$ (pressure)). So, we could say that Gibbs free energy at equilibrium is minimum.
On the ...
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What would be the effect of the addition of an inert gas to a reaction at equilibrium?
Why does a dissociation reaction shift to the right with the addition of an inert gas?
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Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?
Take for instance the reaction
$$\ce{H2(g) + I2(s) <=> 2HI(g)}$$
The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a ...
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Relation between chemical kinetics and chemical equilibrium
In my chemistry book, the law of chemical equilibrium is derived from the law of mass action:
For a reversible chemical reaction $$\ce{aA +bB\rightleftharpoons cC + dD}$$ where $a$, $b$, $c$ and $d$ ...
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What software can calculate aqueous solution equilibria?
What software is available out there to calculate the equilibrium in a set of reactions in aqueous solution? In particular, I'm interested in software general enough to simulate things like titration ...
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Which equilibrium constant is appropriate to use?
I have learnt that the standard free energy change is related to the equilibrium constant of a reaction by,
$$\Delta G^\circ = -RT \ln K$$
Here, does $K$ refer to $K_p$ or $K_c$?
Also, please give ...
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Why does water dissociate to H3O+ and OH- rather than H+ and OH-?
Why does water dissociate to
$\ce{H3O+ + OH-}$
instead of $\ce{H+ + OH-}$?
This question came to surface when I was learning about acids and bases, and learned this definition:
$\mathrm{pH=}-\log_{10}[...
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Why don't everyday things burn?
Ok, so I learned about the equilibrium constant. Now, I've seen that the equilibrium constant of burning is extremely small $(K \ll 1)$. here, I have a question. you see, $K$ is still NOT 0, which ...
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What is the difference between "reaction in both directions" and "equilibrium"?
According to the Wikipedia page on Chemical Equations:
Symbols are used to differentiate between different types of reactions. To denote the type of reaction:
"$=$" symbol is used to denote a ...
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Is carbonyl-enol tautomerization only intermolecular or can it be intramolecular?
During workup of a conjugate addition reaction, it is likely that protonation occurs at the oxygen of the enolate formed. See discussion here: Do enolates get protonated at the carbon or oxygen atom? ...
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Why does the reaction quotient use the products (multiplications) of reactants and products, rather than their respective sums?
As you may know, the reaction quotient $Q_c$ is defined by the equation
$$
Q_c = \frac{[C]^\gamma [D]^\delta}{[A]^\alpha [B]^\beta}
$$
for the chemical reaction
$$
\alpha A + \beta B \rightarrow \...
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Why are equilibrium constants unitless?
I haven’t quite reached the point where I can read a full-fledged text on chemical kinetics and thermodynamics yet, so bear with me, please.
I’m wondering why a value like $K_\text{eq} = \frac{[\ce{...
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Does the number of H+ ions in solution go up on dilution of a weak acid?
In my textbook, a footnote says:
In case of weak acids, on dilution the total number of $\ce{H^{+}}$ ions in solution increases because dissociation of the weak acid increases
This didn't make ...
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How to explain the concept of mol and reactions involving mol quantities
From time to time I do little pro bono lessons for second grade in math, physics, and chemistry. Recently I came across this question.
In a container is $2~\mathrm{mol}$ of $\ce{SO3}$ (sulfur ...
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Can a multi-species system oscillate around equilibrium?
In reading about chemical oscillations such as those that occur in the Belousov–Zhabotinsky reaction (BZ), it's often reported that these reactions were initially not taken seriously, because of a ...
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Is there a difference between equilibrium and steady state?
The term equilibrium is used in the context of reversible reactions that reach a point where concentrations no longer change. The term steady-state is used in enzyme kinetics when the concentration of ...
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Is every chemical reaction in equilibrium?
I read that every chemical reaction is theoretically in equilibrium in an old textbook. If this is true how can a reaction be one way?
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How does a chemical "know" which other species are present and where equilibrium is?
Please forgive me if this is a vague question. I have always wondered how a chemical reaction "knows" where its equilibrium should be. For example, using a basic example of Le Chatelier's principle, ...
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Why does free chlorine in the stratosphere lose its ozone-depleting potential after about 100,000 reactions?
Free chlorine ($\ce{Cl}$) in the stratosphere can deplete ozone ($\ce{O3}$) as follows:
$$\ce{Cl + O3 -> ClO + O2}$$
The chlorine atoms can then react with oxygen and return to the beginning of ...
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Does an irreversible reaction have an equilbrium between reactants and products?
Retrospective analysis 2/13/2017 -- The barium sulfate example is a poor choice. Equilibrium equations should really be defined using activities, and the activity of solid barium sulfate is by ...
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Formation of a stable hydrate
Question: Which of the following does not form a stable hydrate?
I think they mean nucleophilic addition of water. For compound (C), on reaction with water, the product formed is
The product has ...
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Won't the net effect of a catalyst be zero if it creates a new path with lower activation energy?
A catalyst will provide a new path with a lower activation energy (Figure 1). Won't this mean the forward and backward reactions will both speed up (as they both have a lower activation energy path to ...
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Which factors determine the keto:enol ratio for aldehydes, ketones, and 1,3-dicarbonyl compounds?
Arrange the following compounds in order of increasing enol content:
I think the order is D > C > B > A considering conjugation, hyperconjugation and hydrogen bonding. The enol formed in ...
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I'm pretty sure this doesn't follow Le Chatelier's Principle
The likelihood is that I'm misunderstanding what's going on here.
Consider the reaction $\ce{A <=> B}$, where $K_\mathrm{c}=1$.
Initially, the system at equilibrium, where $[\ce A]=\pu{1M}$ ...
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Is the Gibbs standard free energy always constant?
I am a biochemistry student and we are learning about thermodynamics. Is the Gibbs standard free energy for a reaction always constant? The equation below suggests that it changes with temperature:
$$...
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Why is the Haber process carried out at such high temperatures?
On a large scale, ammonia is prepared via the Haber process:
$$\ce{N2(g) + 3H2(g)->2NH3(g)} \qquad \Delta _\mathrm{f}H^\circ = -46.1~\mathrm{kJ \cdot mol^{-1}}$$
The optimum conditions for the ...
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Can a zeroth order reaction be reversible?
After recently studying about chemical equilibrium, I was convinced that the forward and backward reaction rates meet each other at equilibrium.
However thinking about zeroth order reaction annoyed ...
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How is volatility useful in the production of acids?
Sulfuric acid because of its low volatility can be used to manufacture more volatile acids from their corresponding salts.
How does volatility affect the production of acids? Isn't it that sulfuric ...
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What is the Ka of OH- and Kb of H3O+?
What is the $K_\mathrm{a}$ of $\ce{OH^-}$ and $K_\mathrm{b}$ of $\ce{H_3O^+}$? Have these constants been determined?
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Why are weak acids weak?
What are weak acids? My chemistry and biology classes skimmed over them briefly but nothing in depth. I understand that an acid is weak if it partially dissociates and breaks down into ionic compounds,...
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Le Chatelier's principle: Are there any exceptions?
The way Le Chatelier's principle is presented in most introductory chemistry books (high-school) is as though it's an indisputable law of the physical world (in the sense that we're never shown an ...
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Is LiOH a weaker base than NaOH?
Is $\ce{LiOH}$ a weaker base than $\ce{NaOH}$?
Note: I'm not interested in "why," but rather what the "real" $\mathrm{p}K_
\mathrm{b}$ values are.
$$
\begin{array}{lcc}
\text{Data for Alkali Metal ...
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Is there a reason for the mathematical form of the equilibrium constant? [duplicate]
Why are the two molarities multiplied and not added, and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply ...
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What does it mean to shift equilibrium?
What does it mean to shift a chemical equilibrium? For example,
the equilibrium shifts to the left …
I don't understand that.
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What is active mass?
I'm aware of the fact that active mass is defined as the molarity of a substance, but my textbook states that
"Active masses are dimensionless quantities but for our purposes we generally take them ...
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Why can't a reaction go to completion?
What is the reason for why an exergonic reaction would still have some remaining reactants (or an endergonic reaction to have any products)? The explanation given on this page (see Chemical reactions ...
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Apparent paradox in the formation of ice at room temperature
The formation of ice out of liquid water can be written down like this:
$$\ce{H2O (l) <=> H2O(s)}$$
We can calculate the change in standard Gibbs free energy (per mol substance) in the following ...
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What is the molecularity of a reversible reaction?
I know that the definition of molecularity of a reaction is number of species reacting in an elementary step. But considering the theory of microscopic reversibility for elementary reactions, each ...
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How can the equilibrium shift, while Kc remains constant?
Consider the following reversible reaction.
$$\ce{Cr2O7^2-(aq) + H2O(l) <=> 2 CrO4^2-(aq) + 2 H+(aq)}$$
What will happen to the position of equilibrium and the value of $K_c$ when more $\ce{H+}$ ...
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Why exactly does precipitation occur?
In a solution, we have ions floating around but when we have a precipitate, they're arranged as they would be in a solid. This conversion should cause a decrement in the entropy of the system and ...
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How is it that the equilibrium constant does not depend on the mechanism?
For a reaction of the form
$$\ce{aA + bB <=> cC + dD}$$
the equilibrium constant is
$$K_c=\frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{A}]^a[\ce{B}]^b}$$
regardless of the mechanism of the reaction. ...
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Why does the equilibrium constant change on scaling the stoichiometric coefficients of a reaction?
I read in my textbook that if we multiply a chemical reaction by some factor(let's say $b$) its new equilibrium constant becomes $K^b$.But I don't understand why this happens..
What is the difference ...
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Why should a system try to reverse any change that has been done to it?
I understood Le Chatelier's principle perfectly but my question is: Why should a system try to reverse any change that has been done to it?
I understand equilibrium constant, mole concept and ...
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Effect of Temperature on pH of Water
The $K_\mathrm w$ is a function of temperature. It is $10^{-14}$ at $25\ \mathrm{^\circ C}$. When the temperature is $50\ \mathrm{^\circ C}$, the $K_\mathrm w$ can be calculated to be somewhere around ...
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Why does the ionic product of water remain constant after addition of non-neutral solute?
In my textbook, it is given that the ionic product of water $K_\mathrm{w}$ remains constant even when a non-neutral solute such as an acid is added to it.
$$K_\mathrm{w} = \ce{[H3O+][OH-]}$$
When a ...
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Acidity of hydrogen chloride in acetic acid
A question asked to find the $\mathrm pK_\mathrm a$ of $\ce{HCl}$ in acetic acid. The equation of $\ce{HCl}$ disassociating in water is: $$\ce{HCl + CH3COOH \leftrightharpoons CH3COOH2+ + Cl-}$$ I ...
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Quantum mechanical explanation for Le Chatelier's principle?
We know from basic chemistry that a reaction reaches equilibrium as described by Le Châtelier's principle. What's the quantum mechanical explanation to this principle? How a change in temperature/...
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How can a protein folding transition state have zero lifetime?
I'm doing a module on my Biochemistry course looking at protein folding, and in a discussion of [folding] transition states I was a little confused at the thought of a zero-lifetime transition state - ...
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