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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0answers
51 views

How to calculate the value of heat absorption/ heat release during water electrolysis?

The overall reactions with the enthalpies of water electrolysis at room temperature can be represented by the equation below: $$\ce{2H2O + \pu{237.2 kJ mol-1} + \pu{48.6 kJ mol-1} → 2 H2 + O2}$$ ...
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2answers
131 views

Exothermic: enthalpy or heat?

I am used to thinking of exothermic reactions as being defined as having negative $ΔH.$ However, I also am used to hearing/thinking of exothermic reactions as "releasing heat". Since change in ...
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1answer
111 views

Why does Freundlich adsorption isotherm not have a term for surface area?

Why does Freundlich adsorption isotherm not have a term for surface area? The formula given by Freundlich adsorption isotherm: $$ \frac{x}{m}= k P ^{1/n}$$ Where $x$ is the mass of gas adsorbed ...
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1answer
65 views

What drives vibrational cooling in an excited stated?

As we excite a molecule from its ground state, $S_{0,v=0}$, to some excited state in a higher vibrational state, i.e. $S_{1,v'=3}$, what drives vibrational cooling within that excited state manifold (...
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3answers
215 views

Why doesn't beryllium, an elemental solid, obey Dulong and Petit's law?

Beryllium has a molar heat capacity of $\pu{17.7 J mol-1 K-1},$ which is quite far from the $\pu{25 J mol-1 K-1}$ as predicted by Dulong and Petit's law. What is the reason for this discrepancy?
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36 views

Calculate change in entropy when both temperature and volume change

Calculate the change in entropy when $\pu{23.5 g}$ of oxygen gas is heated from $\pu{240 K}$ to $\pu{360 K}$ in such a way that its pressure increases from $\pu{2.00 kPa}$ to $\pu{8.00 kPa}.$ Assume ...
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2answers
190 views

Why is there a z² label for d orbitals, but no x² and y² labels with corresponding shapes?

I know that the $\mathrm{d}_{z^2}$ orbitals are named as a result from the conversion of the angular component of the hydrogen-like wave function in terms of Cartesian coordinates, but how come we ...
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19 views

Changing conditions of gaseous mixture

A gaseous mixture of $\ce{NO2}$ and $\ce{N2O4}$ is sealed in 4 identical vessels with movable pistons. When the conditions are modified as described in 1) to 4), in which condition does the molar ...
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4answers
288 views

Relation between activation energy and rate constant

Consider two types of reaction. One has more activation than other. If we increasing temperature by same amount in both, rate constant of which reaction will increase more? My attempt: as we know ...
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1answer
437 views

Entropy change in non-ideal solutions

We know that some solutions show positive deviations and some show negative deviation from Raoult's law.The former is endothermic and the latter is exothermic. And again, the volume change show ...
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669 views

Which of the following statements is true if HI is formed in the following reaction?

Which of the following statements is true if HI is formed in the following reaction? $$\ce{H2(g) + I2(g) -> 2HI(g)}$$ a. There are no collisions between the reactants in the reaction. ...
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1answer
50 views

Why electrons move to Cu in galvanic cells?

I'm student who learning about chemistry, and I got problem about understanding why electorns move to Cu in galvanic cells. Let's think the reason for electrons going to Cu is that the standard ...
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32 views

Reaction between copper and silver(I) nitrate in aqueous medium

What is the reaction between $\ce{Cu}$ and $\ce{AgNO3}$ taking place in aqueous medium? The answer given was: "Only" oxidation of $\ce{Cu}.$ My concern is: how is only oxidation of $\ce{Cu}$ ...
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1answer
65 views

What does it mean for chemical reaction network to be in equilibrium?

What does being in "equilibrium" mean for a set of chemical reactions? If we have some number $n$ of $\ce{A}$ molecules and $m$ of $\ce{B},$ and the following reaction where $\ce{A}$ and $\ce{B}$ can ...
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1answer
286 views

Decrease in molar conductivity with increase in concentration

Why does molar conductivity $Λ$ for strong electrolytes decrease with increase in concentration? I mean, more concentration would mean higher number of solute particles present in the solution, and as ...
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30 views

How do you remove lumps in reagents without contaminating them?

I think desiccating the powdered reagent would help remove lumps (at least in preventing lump neoformation) but would desiccation alone collapse all lumps in a powder (say KCl as it lumps easily), or ...
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390 views

Kolmogorov backward equations in active biological systems

I am trying to understand the following equations from a paper by Wang et al. [1, p. 5 at the SI]: Michaelis–Menten Representation of the Kinesin Cycle We assumed that there is a strong ...
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Is there any formula for finding out probable distance of orbitals or do I just remember the values? [closed]

Like, do I need to just remember that it is less in 3d than 3s and so on?
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1answer
27 views

Dosing leaves with Zinc Nitrate for pollution experiment - Need specific concentration

I am trying to assess the pollution tolerance of an insect using Zn as a proxy. I have a supply of Zinc Nitrate Hexahydrate that I want to use to contaminate dried leaves (the insect's food). The LD50 ...
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1answer
52 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
163 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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2answers
180 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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1answer
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
136 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
60 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
67 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
692 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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2answers
251 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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2answers
179 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
288 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
85 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{...
2
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1answer
37 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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81 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 ...
4
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1answer
98 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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1answer
60 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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1answer
62 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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2answers
83 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
65 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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1answer
232 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
715 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
94 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
206 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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1answer
77 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
104 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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0answers
31 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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0answers
39 views

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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2answers
212 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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1answer
114 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 ...
2
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2answers
167 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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