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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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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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
$$
\alpha A + \beta B \rightarrow \...
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Which equilibrium constant is appropriate to use?
I have learnt that the standard free energy change is related to the equilibrium constant of a reaction by,
$$\Delta G^\circ = -RT \ln K$$
Here, does $K$ refer to $K_p$ or $K_c$?
Also, please give ...
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Is a negative pH level physically possible?
A friend of mine was looking over the definition of pH and was wondering if it is possible to have a negative pH. From the equation below, it certainly seems mathematically possible—if you have a $1.1$...
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Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?
Take for instance the reaction
$$\ce{H2(g) + I2(s) <=> 2HI(g)}$$
The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a ...
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Is there a reason for the mathematical form of the equilibrium constant? [duplicate]
Why are the two molarities multiplied and not added, and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply ...
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What is wrong in this argument that dG must always be zero?
Under constant temperature and pressure, the change of the Gibbs free energy can be written as
$$\mathrm dG_\textrm{sys} = \mathrm dH_\mathrm{sys} - T\,\mathrm dS_\mathrm{sys}$$
And in the textbook ...
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What does it mean to shift equilibrium?
What does it mean to shift a chemical equilibrium? For example,
the equilibrium shifts to the left …
I don't understand that.
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How is it that the equilibrium constant does not depend on the mechanism?
For a reaction of the form
$$\ce{aA + bB <=> cC + dD}$$
the equilibrium constant is
$$K_c=\frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{A}]^a[\ce{B}]^b}$$
regardless of the mechanism of the reaction. ...
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Le Châtelier's Principle and heat
Consider the following reaction at equilibrium.
$$\ce{A->B}, \Delta H < 0 $$
Suppose I increase the temperature. Now, quite a few people would invoke Le Châtelier's Principle and say that since ...
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Calculate pH of a mixture of a strong base and acid. Knowing only the pH, wt/v%, and volume of both solution. [closed]
Title explains all. I have been stuck on this for an hour and for some reason cannot understand it. I have tried to do an ICE table but get stuck halfway as I do not know whether I would use the w/v ...
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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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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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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 inverse relationship between the strengths of an acid and its conjugate base appear to be violated in the case of chloric(I) acid?
Hypochlorous acid is a weak acid with $\mathrm{p}K_\mathrm{a}(\ce{HClO}) = 7.53$. Then why is its conjugate base, $\ce{ClO-}$, a weak base in water? Shouldn't the strength of the base be inversely ...
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Why are activities of solids and liquids taken to be unity?
First, I should mention that the question was already asked here: Why is active mass of a pure solid or liquid always taken as unity?
However, the treatment there is qualitative and I do not really ...
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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}$$ where $a$, $b$, $c$ and $d$ ...
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Does the number of H+ ions in solution go up on dilution of a weak acid?
In my textbook, a footnote says:
In case of weak acids, on dilution the total number of $\ce{H^{+}}$ ions in solution increases because dissociation of the weak acid increases
This didn't make ...
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What is the Ka of OH- and Kb of H3O+?
What is the $K_\mathrm{a}$ of $\ce{OH^-}$ and $K_\mathrm{b}$ of $\ce{H_3O^+}$? Have these constants been determined?
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How can the equilibrium shift, while Kc remains constant?
Consider the following reversible reaction.
$$\ce{Cr2O7^2-(aq) + H2O(l) <=> 2 CrO4^2-(aq) + 2 H+(aq)}$$
What will happen to the position of equilibrium and the value of $K_c$ when more $\ce{H+}$ ...
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Why is water not part of the equilibrium constant?
In the acid base reaction
$$\ce{NH4+ + H2O <-> NH3 + H3O+}$$
the acidity constant, which is a relation between concentrations is given by
$$K_{\mathrm{a}}=\frac {\ce{[NH3]} \cdot \ce{[H3O+]}}{...
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Why does the equilibrium constant depend on the temperature but not on pressure and concentration?
According to my textbook (and intuitively) certain changes when the aforementioned 3 variables are altered occur in accordance with Le Chatelier's Principle. However, what I don't understand is what ...
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What are the units of Kc and Kp?
They are both equilibrium constants as far as I know.
Kc is in terms of molarity and Kp is in terms of pressure. Also both of them are ratios of respective quantities [ ratio of molarity(s) in Kc and ...
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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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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 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 ...
user33789
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What is the correct unit for the equilibrium constant?
I have the following equation
$$K_a = \dfrac{c\alpha^2}{1-\alpha},$$
with units $c= \pu{mol/cm^3}$ and $\alpha$ is the same. I'm not sure how to get the correct units for $K_a$. What I have come up ...
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Derivation of relationship between equilibrium constant and Gibbs free energy change
Why is $\Delta G=\Delta G^o+RT\ln Q?$
It feels like all online sources were written for introductory Chemistry students! Where do I find a rigorous proof of this identity? Greatly appreciate it!
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Find the pH of an amphiprotic salt dissolved in water at room temperature
Let's say I have a polyprotic acid $\ce{H2A}$ with the following properties:
$$
\begin{align}
\ce{H2A &<=> HA- + H+} & K_1 &= 1\cdot 10^{-1}\\
\ce{HA- &<=> A^2-+ H+} & ...
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Why does equilibrium exist?
I've read an article that equilibrium exists when $G$ (Gibbs free energy) becomes minimum. If formation of products decreases Gibbs free energy, why won't the reaction proceed to completion so that ...
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Chemical Equilibrium - Why do changes in pressure cause a shift in the ratio of products and reactants?
I understand Le Chatelier's principle and how every change to an equilibrium system causes an opposing reaction from the system. I also understand how, when pressure is increased, the equilibrium ...
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Why don't everyday things burn?
Ok, so I learned about the equilibrium constant. Now, I've seen that the equilibrium constant of burning is extremely small $(K \ll 1)$. here, I have a question. you see, $K$ is still NOT 0, which ...
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Can a multi-species system oscillate around equilibrium?
In reading about chemical oscillations such as those that occur in the Belousov–Zhabotinsky reaction (BZ), it's often reported that these reactions were initially not taken seriously, because of a ...
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Is there a difference between equilibrium and steady state?
The term equilibrium is used in the context of reversible reactions that reach a point where concentrations no longer change. The term steady-state is used in enzyme kinetics when the concentration of ...
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Why does free chlorine in the stratosphere lose its ozone-depleting potential after about 100,000 reactions?
Free chlorine ($\ce{Cl}$) in the stratosphere can deplete ozone ($\ce{O3}$) as follows:
$$\ce{Cl + O3 -> ClO + O2}$$
The chlorine atoms can then react with oxygen and return to the beginning of ...
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Formation of a stable hydrate
Question: Which of the following does not form a stable hydrate?
I think they mean nucleophilic addition of water. For compound (C), on reaction with water, the product formed is
The product has ...
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Does an irreversible reaction have an equilbrium between reactants and products?
Retrospective analysis 2/13/2017 -- The barium sulfate example is a poor choice. Equilibrium equations should really be defined using activities, and the activity of solid barium sulfate is by ...
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Which factors determine the keto:enol ratio for aldehydes, ketones, and 1,3-dicarbonyl compounds?
Arrange the following compounds in order of increasing enol content:
I think the order is D > C > B > A considering conjugation, hyperconjugation and hydrogen bonding. The enol formed in ...
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How to determine the pH of a mixture of two weak acids?
We have two solutions:
Solution 1 is $\ce{HCOOH}$, its concentration is $c_1 = \pu{10^-2 mol/l}$, its volume is $V_1 = \pu{50 ml}$, and its $\mathrm{pH}_1 = 2.9$.
Solution 2 is $\ce{CH3COOH}$, its ...
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Why do liquids and solids have constant concentrations?
I don't understand why liquids and solids have constant concentrations. Can anyone explain this to be in simple terms?
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How do equilibrium shifts affect solids?
Say we have the following reversible reaction: $$\ce{NaOH{(s) }<=> Na^+{(aq) }$+ $OH^{-}{(aq)}} +10.6 \mathrm{kcal}$$
If we add $\ce{OH^-}$ and equilibrium shifts to the left, does that affect ...
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Pressure at which graphite and diamond are in equilibrium
The standard state Gibbs free energies of formation of graphite and diamond at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively.
The conversion of graphite to diamond ...
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Le Chatelier's principle with pure solids and liquids
In the following reaction:
$$\ce{A(s) <=> B(g) + C(g)}$$
since adding a pure solid is not supposed to shift the equilibrium in any way, does that mean that I can essentially remove all of the ...
user28295
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What is the difference between the equilibrium position and the equilibrium constant?
I used to think that the equilibrium constant was a quantitative measure of the equilibrium. However, changing concentration and pressure in a system at equilibrium that shifts the equilibrium doesn't ...
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How concentrated can an acid be?
How concentrated can an acid be without it being supersaturated? Is there a certain limit to how concentrated an acid or base can be?
When I mean concentration, I mean molarity; so how concentrated ...
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Which make HCO3- to show two pH values at two scenarios?
According to the below two titrations,
Image Reference
If we consider the reactions, at the first reaction (in first figure after adding 1.0), there is $\ce{HCO3-, NaCl,}$ and $\ce{H2O}$ at the first ...
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Why is the rate of a reaction proportional to the concentrations of reactants raised to their stoichiometric coefficients?
Consider a gaseous state elementary reaction $$\ce{aA(g) + bB(g)} \overset{k_\mathrm{f}}{\underset{k_{\mathrm{b}}}{\ce{<=>}}}\ce{ cC(g) + dD(g)}$$
I know that for this reaction, $$\Delta G = \...
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pH of ammonium acetate solution
I'm trying to calculate the pH of a 1M $\ce{NH_4CH_3COO}$. I know that I'll have these reactions:
$\ce{NH_4CH_3COO <=> NH_4^+ + CH_3COO^-}$
$\ce{NH_4^+ <=> NH_3 + H^+}$
$\ce{CH_3COOH <=...
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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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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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