Questions tagged [physical-chemistry]

The study of chemical systems using the laws and concepts of physics. This usually requires the techniques of thermodynamics, statistical mechanics and quantum mechanics.

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38 views

What molecules are produced in carbon arc lamp and how do they produce light?

I am curious about the chemistry of the arc lamp (an indirectly for the incandescent bulbs) thus I would like to ask the following. It is a common understanding that the electrons pushed inside an ...
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0answers
113 views

A tricky question in Eudiometry/Gas analysis

In a eudiometer $\pu{14 ml}$ of $\ce{CH4}$ and $\pu{38.5 ml}$ of $\ce{O2}$ was introduced. After explosion and cooling to initial temperature ($\pu{23°C}$) the volume of eudiometer was found to be $\...
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112 views

What is the physical meaning of fractional oxidation numbers of elements in compound

Many times I encounter oxidation numbers like -1 in the peroxide for oxygen, -1/2 in superoxide, and in some other compounds some elements have 8/3 or such like that...what is the physical meaning of ...
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2k views

What does “lit.” mean in boiling point or melting point specification?

For example, this Xanthene 99% specification from Sigma Aldrich states: \begin{array} \\\hline \text{bp} & 310-312 ~^\circ\mathrm{C~ (lit.)} \\\hline \text{mp} & 101-102 ~^\circ\mathrm{C~ (...
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1answer
100 views

Equilibrium constant for a solid-solid equilibrium

Suppose there are two equations: $$ \begin{align} \ce{A(s) &<=> B(g) + C(s)} &\quad &K_1 \tag{R1}\\ \ce{B(g) &<=> D(s) + E(s)} &\quad &K_2 \tag{R2} \end{align}$$ ...
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1answer
56 views

Steady State Approximation final integral proof $\frac{d[P]}{d t}=k_{a}[A]$ yielding $[P]=\left(1-e^{-k_{a} t}\right)[A]_{0}$

I want to ask a question about the Steady State Approximation integral. I understand the steady state integral works in Leyman's terms as the intermediate is formed as fast as it is consumed so the ...
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2answers
60 views

Statistical thermodynamics [closed]

Entropy of indistinguishable particles $S$ is $$S = k\ln W,$$ but in some places notation is different: $$S = k\ln Q + \frac{U}{T}$$ Can you explain, please?
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Image formation in LEEM

currently I'm studying for my master's examination in physical chemistry. The topic will be surfaces and catalysis. To prepare myself I'm reading "Surface Science - An introduction" by Oura. ...
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3answers
389 views

How to explain disagreement between Le Châtelier's principle and the simplified Gibbs free energy equation?

For example, for the dissolution of a salt in water that is exothermic, heating the solution would drive the reaction towards the solid form of the salt according to Le Châtelier's principle. However,...
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149 views

Having a contradiction while deriving Gay-Lussac's law using Boyle's law and Charles' law

From Boyle's law: $$P_1V_1 = P_2V_2 \quad\implies\quad V_2 = \frac{P_1V_1}{P_2} \label{eqn:boyle}\tag{1}$$ From Charles' law: $$\frac{V_1}{T_1} = \frac{V_2}{T_2} \quad\implies\quad V_2 = \frac{...
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175 views

Derivation of time probability distributions for single molecule kinetics

If we have a protein $\ce{A}$ that can bind to protein $\ce{B}$: $$\ce{A + B <=>[$k_\mathrm{fwd,1}$][$k_\mathrm{rev,1}$] AB}$$ and the bound complex $\ce{AB}$ can be converted into $\ce{C}$: $...
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1answer
104 views

Confusion regarding calculating the pH of a salt of weak acid and weak base

I need to calculate the $\mathrm{pH}$ of a salt of weak acid and weak base in an aqueous solution. Method I used for calculation For a salt of weak acid and weak base (assuming complete dissociation ...
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1answer
60 views

Ammonium chloride in aqueous solution

When Ammonium chloride is in an aqueous medium its cation part ammonium undergo hydrolysis. Since ammonium is conjugate acid of a weak base it readily release one $\ce{H+}$ and converts back to $\ce{...
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1answer
36 views

Is there a relationship between loss of electrons and EM wave reflection? [closed]

Is there a relationship between the loss of electrons in a cation and the amount of electromagnetic spectrum, a compound of this cation would subsequently reflect or transmit? For example, any ...
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64 views

How can the potential energy at the infinite energy level in an atom be zero?

I have recently learnt about atomic structure and the Bohr model of the atom and have observed a discrepancy between it and my previous knowledge based on physics. For simplicity, assume the atom is ...
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1answer
96 views

How does equalizing voltage for lead acid battery depend on the temperature?

I am using advanced lead-carbon batteries (these ones) in an off-grid solar system. The spec specifies equalizing voltage 14.1 V for 12 V block @ 25 °C (77 °F). I keep the batteries in an outdoor shed,...
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56 views

As you heat up a substance will it's bonds begin to dissipate?

As you heat something up does it slowly start to dissipate? Water, for instance, boils at 100 degrees Celsius, but if you are heating it up at 90 degrees will its bonds be weaker?
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56 views

Is activation energy time-dependent?

I was thinking lately about activation energy's dependency on time. I couldn't find any information on the internet. Only answer that came up to my mind is the fact that activation energy is constant, ...
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79 views

Do maxima in Gibbs energy also correspond to equilibrium positions?

ΔrG=(∂G/∂ξ ) at constant p and constant T, where ξ is the extent of reaction. By Second Law implication, ΔrG= 0= (∂G/∂ξ ) at equilibrium. If we consider a graph of G against ξ, this would mean we ...
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1answer
62 views

Mechanism of burning of hydrogen [duplicate]

So I was curious regarding a simple chemical equation : $$\ce{2 H2 + O2 -> 2 H2O}$$ You add heat to the system (i.e fire) and you get water vapor. I'm curious of understanding the mechanism, ...
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207 views

How does increase in volume change the speed of reaction in production of NO2?

$$\ce{2 NO + O2 <=> 2 NO2}$$ I understand that increasing the volume $×2$ means lower pressure so production of $\ce{NO2}$ is slowed down, but when asked how to express this mathematicaly I can'...
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1answer
440 views

Electrode potential for metal-metal ion and metal-metal insoluble salt-salt ion electrode

So I read it in a book that The potential of metal-metal ion electrode and metal-metal insoluble salt-salt anion electrode is same while their standard potentials are not same. Standard potential ...
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2answers
74 views

Rate law of the reaction of propane with oxygen

In class, I have a demonstration where I light a bubble filled with propane. As I add oxygen, the bubbles combust faster and more quickly. I have already balanced out the chemical reaction like so: $$...
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1answer
131 views

Hill equation with inhibition and activation

The Hill equation for an activating enzymatic interaction with cooperative multiplicity $n$ is $$\frac{\mathrm d[\ce{P}]}{\mathrm dt} = V_\mathrm{max}\frac{[\ce{S}]^n}{K_\ce{S} + [\ce{S}]^n}\tag{1}$$ ...
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75 views

Distribution of polymer lengths

Suppose we have a chemical reaction where a linear chain can form (reversibly) from building blocks (e.g. atoms or molecules): $$\ce{X_$i$ + X_$k$ <=>[$k_\mathrm{fwd}$][$k_\mathrm{rev}$] X_$i$...
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1answer
77 views

Boiling point of liquids [closed]

If we can have liquid - vapour equilibrium at any temperature what is the 'point' behind boiling point.Boiling point is just a special case of liquid - vapour equilibrium where partial pressure equals ...
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27 views

Adding pure solid/liquid in heterogeneous equilibrium [duplicate]

If I have the heterogeneous equilibrium $$\ce{aA(s) + bB(g) <=> cC(g) + dD(g)}$$ I understand that the equilibrium expression is $$K_c = \frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{B}]^b}$$ and that $\...
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Are there any surface treatments that would make calcium usable for metallurgy?

Calcium is the best conductor for its weight, but the soluble powdery oxide makes it impractical for use in power lines. Are there any surface treatments or alloying processes that could help? (...
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125 views

Y-axis of the reaction co-ordinate graph

In the graph of the reaction co-ordinate, is the $y$-axis that is used $∆H,$ $∆U$ or $∆G$?
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107 views

How can hydrogen and oxygen coexist in high temperature? Where did the oxygen come from?

A gasification worked with the combustion of bio pallets with production of syn gases. Pure oxygen and $\ce{H2O}$ were fed into the combustion reactor to combust the pallets with no opening of any syn ...
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2answers
116 views

Interpretation of Raoult law

In attachment I have tried to derive Raoult's law by using the concept of equilibrium constant. There is nothing mentioned in my text book about how this equation comes about, so I decided to do it ...
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1answer
112 views

What actually happens when 'energy is released'? [duplicate]

Thermodynamics classes and equations always discuss a chemical reaction in the form of energy being released or absorbed. This is always hand-waved as just 'energy' from the surroundings. What's ...
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29 views

Two different answers obtained by balancing this chemical equation!! Somehow [duplicate]

This is the concerned equation: $\ce{ XeF4 + H2O -> Xe + XeO3 + HF + O2}$ This can be balanced as $\ce{6 XeF4 + 12 H2O -> 4 Xe + 2 XeO3 + 24HF + 3 O2}$ or $\ce{5 XeF4 + 10H2O ->3 Xe + ...
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1answer
30 views

Understanding “Gay-Lussac's law of Gaseous volumes/combining volumes”

Understanding "Gay-Lussac's law of Gaseous volumes/combining volumes". So I was reading Wikipedia and stumble across this. It defines it as follows "The ratio between the volumes of the reactant gases ...
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92 views

Henry law and equilibrium

Is Henry's law a consequence of the equilibrium between a substance S in aqueous phase and the same substance S in gaseous phase? What I mean is, is it correct to treat Henry law as a manipulation of ...
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40 views

Le Chatelier's Principle Having No Effect

Consider the following equilibrium system: $$\ce{2 IBr(g) <=> I2(g) + Br2(g)}$$ Would a decrease in the volume of the system effect the equilibrium? I think it would not affect the ...
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1answer
131 views

Thermodynamics: ΔU = Q + W or U = Q?

Heat is the total kinetic energy of all atoms of the system. When work is done on the system it means that a part of system kinetic energy is used to do the work, and this work makes the surrounding ...
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1answer
30 views

Find ratio of quantities of water and of argon in airtight container

I am working on my EJU exam past papers (2013) and got stuck at this question. Knowledge of high school or first year university chemistry is assumed. I honestly do not know where I should start. ...
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2answers
131 views

Implication of negative order on kinetics

In the reaction $$\ce{2 O3 -> 3 O2}$$ the order of reaction that I have been taught is $$\ce{O_3 \underset{$k_{-1}$}{\overset{$k_{1}$}{<=>}} O_2 + O}$$ $$\ce{O_3 + O \overset{$k_{2}$}{->...
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186 views

Calculating ΔG at the extremes of reaction extent

This question follows on from a great post on comparing $\Delta_\mathrm{r} G^{\circ}$ to $\Delta_\mathrm{r} G$ answered here The G vs ξ graph that is used in the answer is an excellent tool to ...
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1answer
32 views

Help reading a phase diagram? [closed]

How does the y axis work? If the pressure I am looking for is 10^‐4 to 10^‐3 nbar? I tried doing log of the yaxis but its giving me numbers that are not even close to what I am looking for.
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183 views

Changes in entropy and Gibbs free energy for sublimation at triple point [closed]

The standard enthalpy of sublimation of dry ice (solid carbon dioxide) is $\Delta H=6.03\ \mathrm{kJ/mol}$. The triple point of $\ce{CO2}$ is at $p=5.1\ \mathrm{atm}$, $T=-56.7\ \mathrm{^\circ C}$. I ...
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85 views

Why is the entropy of solidifying solution higher than that of a pure solvent?

According to a source, Solutions have a greater entropy than pure liquids as the particles in a solution are more separated and solvent molecules separate the solute particles. If the number of ...
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40 views

Surface chemistry [closed]

Why doesn't the process of chemisorption form multimolecular layers whereas he physisorption with lesser force of attraction between molecules form multimolecular layer?
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45 views

How can I find the emf of a cell given the individual reduction and oxidation reactions and their respective potentials? [duplicate]

If I am given the individual oxidation and reduction half-equations, how can I find the emf of the combination? For example: $$ \begin{align} E^\circ(\ce{Fe^3+}/\ce{Fe^2+}) &= \pu{0.77 V}\\ E^\...
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27 views

Why does internal rotation of ethane give an energy spectrum asymptotically approaching a rotation based on $\nu=1$ rather than $\nu=0$?

I'm a physicist with very little knowledge of chemistry. Recently a chem colleague left a molecular model in my classroom, so I brought it back to her, and as I was walking down the hall with it, a ...
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42 views

Gibbs free energy of activation and activation energy [duplicate]

What the difference between Gibbs free energy of activation and activation energy
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1answer
59 views

In a galvanic cell, why do electrons move through the wire from zinc to copper?

I understand that there is aqueous $\ce{Cu^2+}$ in this scenario which pulls on the electrons from the zinc causing the electrons to move through the wire, but how does the electronegativity of $\ce{...
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48 views

Gibbs energy at a certain temperature

For the reaction $$\ce{1/2 N2(g) + 3/2 H2(g) -> NH3(g)}$$ $ΔG$ at $\pu{298.15 K}$ is $\pu{-3980 cal},$ and the change in enthalpy is given by the expression: $$ΔH = -9.19 - 7.12T + 3....
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1answer
405 views

Is a hydrogen molecule smaller than hydrogen atom?

Recently I came across a textbook of physical chemistry which stated the following: In the formation of a stable hydrogen molecule, two hydrogen atoms share a pair of electrons between them and two ...