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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Calculating Kp in two different ways

The degree of dissociation of $\ce{NH3}$ at $\pu{1 atm}$ is 20 % as follows: $$\ce{2NH3 <=> N2 + 3H2} $$ I follow two ways but end up with two different answers. Here, I assume that ...
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4k views

Find the half equivalence point

How to find the half equivalence point knowing the pH, molarity, titrant added at equivalence point? This a fairly straightforward and simple question, however I have found many different answers to ...
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Ionic Product of Water

Why is the ionic product for water ($K_\text{w}$) temperature dependent? The concentration of $\ce{H+}$ and $\ce{OH-}$ ions in pure water is $[\ce{H+}] = [\ce{OH-}] = 1.0\times 10^{-7}\ \mathrm{mol/l}$...
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What is the value of dissociation constant of water at 25°C [duplicate]

According to my class notes, $$ K_{dissociation} = \frac {[H^+][OH^-]}{[H_2 O]} $$ $$ = \frac {10^{-14} }{55.55} $$ $$ = 1.8 * 10^{-16} $$ But shouldn't we ignore concentration of water (55.55 M) as ...
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How identify acid and base for Henderson-Hasselbach equation [closed]

If I am asked to determine the pH in e.g. 60 mM Na2CO3 and 30 mM NaHCO3 or 50 mM NaHSO4 and 40 mM Na2SO4 How do I go about to identify which of these two is the base and which is the acid? ...
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Finding the molarity of an unknown weak acid when its pH and volume is given

In lab we measured the pH of $\pu{25.0 mL}$ of an unknown acid. The pH was $2.43$. I’m supposed to figure out the molarity. How? I don’t know the $K_a$ or anything. Volume seems useless. I really just ...
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equilibrium reactions [closed]

How will the equilibrium of following reactions be affected 1) N2(g) + O2 (g) ⇄ 2NO(g); 2) 4HCl(g) + O2(g) ⇄ 2Cl2(g) + 2H2O(g) a) by rise of pressure; b) by decrease of oxygen concentration? Explain ...
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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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722 views

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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Why is water ignored in the ionic equilibrium of HF?

While trying to understand the solution of a problem given in my textbook, I realized I'm having some difficulty with the solution. The problem is as follows: The ionization constant of $\ce{HF}$ ...
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Description of a van't Hoff apparatus

A "van't Hoff apparatus" is mentioned as a means of performing a reaction involving gases in a reversible manner, for instance here. Unfortunately I have been unable to find a description of such a ...
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25 views

Is Gibbs energy minimized for processes at constant temperature are pressure only?

I've had this doubt for quite a while, This link https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Map%3A_Physical_Chemistry_for_the_Biosciences_(Chang)/04%...
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2answers
132 views

Calculating pH of rain water

The concentration of $\ce{SO2}$ in the atmosphere over a city on a certain day is $\pu{10 ppm}$. Given that solubility of $\ce{SO2}$ in water is $\pu{1.3653 mol L-1}$ and $\mathrm{p}K_\mathrm{a}$ of $\...
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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? (I am still new to the topic of equilibrium, so please explain in simple words.)
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Chemical Equilibrium - Le Chatelier's Principle, Change in Volume

Question: Consider the following reaction at equilibrium at a total pressure that we will call $P_1$. $$\ce{2 SO2(g) + O2(g) <=> 2 SO3(g)}$$ Suppose the volume of the system is ...
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Le Chatelier's Rule: Relationship between Pressure and Reaction when moles of reactant and products are the same

Consider the equation: $\ce{H2(g) + CO2(g) <=> H2O(g) +CO(g)}$ Indicate how each of the following changes affects the amount of each gas in the system: (a) Decrease in the volume of the ...
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1answer
120 views

Is the active mass of every solid and liquid taken to be unity?

I learnt from my textbook and the question/answer - Why is active mass of a pure solid or liquid always taken as unity? that active mass of a solid or liquid is taken to be unity as: $$[A]=\frac n V=\...
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3answers
65 views

Reaction of Fe2+ and S2- to form FeS

Consider this reaction: $$\ce{Fe^{2+} (aq) + S^{2-} (aq) <=> FeS (s)}$$ The equilibrium constant for the reaction is $1.6 \times 10^{17}$ at $\pu{298K}$. If equal volumes of $\pu{0.06 M}$ ...
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Proof for Arrhenius equation [closed]

The Arrhenius equation states that: $$k=A\mathrm e^{\frac{-E_\mathrm a}{R T}}$$ What is the mathematical proof for this equation?
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1answer
54 views

How to derive the steady-state solution for simple two-step reaction with differential equations? [closed]

Consider this simple two step reaction, a variant of a Michaelis-Menten type of problem, where $\ce{A}$ and $\ce{B}$ reversibly bind to make $\ce{AB}$, and $\ce{AB}$ and $\ce{C}$ reversibly bind to ...
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Is the evaporation (liquid to gas conversion) of ethanol dependent on how full you fill it up in a sealed bottle?

It seems intuitive to think that in a bottle (which is air-tight), if you fill up ethanol (or any other volatile liquid) to very full extent, thereby leaving very little headspace, the amount of ...
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28 views

Temperature in Le Chatelier's principle [duplicate]

Suppose I have a reversible reaction and the forward reaction is endothermic. Now if I increase the temperature, the rate of the forward reaction will increase but as I increase the temperature, the ...
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1answer
59 views

Why is the voltage produced by a voltaic cell affected by temperature as described by the Nernst Equation?

I understand why changing the concentrations of the electrolytes in a voltaic cell affects the voltage. Given a zinc-copper cell for example, if I were to increase the concentration of the zinc ...
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How to find the value of $K_c$?

This is part of my homework. Given the chemical equation : $$\ce{Sb2S3_{(s)} + 3H2_{(g)} <=>2Sb_{(s)} + 3H2S_{(g)}}\text{ }K_{p}=0,429\text{ at }713\text{K}$$ What is the value of $K_c$ ...
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954 views

Understanding the solubility of Ca(HCO3)2

According to wikipedia Ca(HCO3)2 has the following solubility values: 16.1 g/100 mL (0 °C) 16.6 g/100 mL (20 °C) 18.4 g/100 mL (100 °C) So I assume Ca(HCO3)2 would precipitate beyond this level. ...
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229 views

Clausius–Clapeyron relation for states of water and vapor

I've seen many questions about this topic on this site, but I still have some issues trying to understand this aspect. Here's what I believe I understood looking at the phase diagram for a pure ...
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Would the same equilibrium concentration of carbon dioxide, carbon monoxide and oxygen always result for a given initial atomic carbon fraction?

Chemistry SE Question: Starting with a gas mixture of some combination of gases containing carbon and oxygen with a total carbon atomic fraction $f$, would it always reach the same equilibrium ...
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Help required with calculation of reaction rate for a chemical reaction

*Note: This is not a homework problem but something related to my research! Thanks I'm simulating a metal droplet suspended in a reactive medium. The droplet tends to react with the injected gas as ...
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Changes in which factors affect both the rate and the rate constant of a first order reaction?

Changes in which factors affect both the rate and the rate constant of a first order reaction? I. temperature II. concentration (A) I only (B) II only (C) Both I and II (D) ...
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Finding Ka of a monoprotic weak acid from pH and concentration of added sodium salt

A solution of $\pu{0.36 M}$ of the sodium salt of a generic monoprotic weak acid $\ce{HA}$ has a $\mathrm{pH}$ value of $8.782.$ $K_\mathrm{a} = ?$ Why doesn't the following formula work in this ...
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1answer
21 views

What exactly is the requirement (in terms of saturation) for a reaction to be at equilibrium? [closed]

A saturated solution is a solution that contains the max amount of solute able to be dissolved. However, can't a solution still be at equilibrium if you add more solute to a saturated solution as long ...
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1answer
40 views

Can rate constant for forward reaction be equal to rate constant for backward reaction? [duplicate]

For a particular reaction, can we have $K_c = 1$? My confusion arised when I was studying the effect of temperature on $K_c$ . I see that the temperature must affect forward and backward rate ...
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Hydrogen disulfide heterogenous equilibrium

I have been struggling with the following problem for quite a while: I was able to calculate the Gibbs free energy and the equilibrium constant, using the formula $$ΔG = -RT\ln K$$ and ...
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2answers
501 views

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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Derivation of van 't Hoff equation for temperature dependence of equilibrium constant

While I was reading about the usefulness of the quantity $\Delta H$, I found that it can be used to calculate the how the equilibrium constant varies with temperature. How can this be done? Does it ...
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46 views

Delta G in an equilbrium reaction(forward and backward)

Consider a reaction say $$\ce{A + B <=> C + D}$$ Now $\Delta G$ for the forward reaction is: $$\Delta H - T\Delta S$$ For the backward reaction $\Delta H$ and $\Delta S$ are clearly the same ...
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50 views

Equation of water at triple point

I was thinking about what exactly happens at the triple point of water, and what could be the effect of adding solutes/solvents. I feel we can represent the triple point using the following ...
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How does the equilibrium shift when concentration of reactant and product are increased simulatenously

Before answering my question, take a look at this example $$\ce{2NOCl <=> 2NO + Cl2}$$ Let's suppose I have 2 mol/l $\ce{NOCl}$, 2 mol/l $\ce{NO}$, and 1 mol/l $\ce{Cl2}$ in a closed system. ...
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Deprotonated form of phenolphthalein

The wikipedia page states clearly that the coloured form of phenolphthalein is the one with two protons removed. What is the evidence that phenolphthalein loses both protons in basic solution? And ...
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How to account for the common ion effect on osmolarity quantitatively?

In adjusting the osmolarity of a solution of Benzalknonium Cl, Disodium Editate, and Disodium borate/boric acid buffer to be isotonic (about 290 mOsm), the addition of NaCl showed unexpected behavior, ...
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how to Find $P_{tot}$ Given that $K_p = 28.5$ and the partial pressure at equilibrium

I have the equilibrium equation : $4KO_2{_{(s)}} + 2CO_2{_{(g)}} \ce{<=>} 2K_2CO_3{_{(s)}} + 3O_2{_{(g)}}~~k_p = 28.5 ~at ~25C$. Given that The partial Pressure of $CO_2$ is $0.191~atm$ at ...
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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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1answer
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How to explain that an increase in temperature favours an endothermic reaction?

I'm trying to explain how a change in temperature favours an endothermic/exothermic reaction from a collision theory point of view, but I'm not really familiar with the concept just yet. For an ...
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1answer
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Question about change in pressure and change in temperature for system at equilibrium

I was reading my Chemistry textbook and I noticed that it stated that for a system at equilibrium: At constant temperature, reducing the volume of gaseous equilibrium mixture causes the system to ...
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99 views

Will NaF + CaCO3 precipitate much CaF2?

If I mix sodium fluoride, calcium carbonate powder, and water, under what conditions (if any) would there be an equilibrium? I.e. assume we start out with fully dissociated $\ce{Na+(aq) + F-(aq)}$, ...
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1answer
31 views

Is there a name, or any specific jargon for a precipitation equilibrium involving a solid reactant?

Let's say you have some ions in solution, for example Na+(aq) and OH-(aq), and some partially dissolved solid, MgCO3(s), Mg+2(aq) and CO3-2(aq), which precipitates Mg(OH)2(s) until equilibrium. So ...
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1answer
257 views

Apparent contradiction in the type of deviation of an ethanol-water mixture

For a mixture of $\ce{EtOH}$ and $\ce{H2O}$: $\Delta H_{\text{mix}} < 0$ (exothermic) and $\Delta V_{\text{mix}} < 0$ (volume contraction). This means that the unlike interactions are stronger ...
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How to manage complex equilibria when studying a mecanism?

Consider a complex multistep reaction mechanism with several intermediates. There are multiple possible pathways as well as equilibria in solution. One wants to study the reaction mechanism using ...
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2answers
125 views

Kinetics of converting a water + heavy water mixture to HDO

Imagine an initial 50%-50% mixture of normal ($\rm H_2 \rm O$) and heavy water ($\rm D_2 \rm O$). I think, simply mixing them, the result will exponentially converge to an equilibric state, where ...
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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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