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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If most drugs are made from hydrogen, nitrogen, oxygen, and carbon, then why can't I make drugs out of the air? [closed]

If most drugs are made from hydrogen, nitrogen, oxygen, and carbon, then why can't I make drugs out of the air? Is there a name for using photons to excite the atomic structure of gas to change its ...
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Question regarding Entropy [closed]

I had some doubts regarding the concept of entropy. My first doubt was Entropy is defined as $ dS = dQ _{rev}/ T $ yet my textbook says that entropy is a state function. Isn't it the definition of a ...
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How Does Peroxide + UV = Oxidation?

I restore shoes, & we have this method for oxidizing the translucent soles to get them to look new again. The process is: clean surface Apply 40 Volume peroxide cream Place under UV Growlight. I ...
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115 views

Is the rate of electrolysis the same throughout as long as voltage is same

In an electrolytic cell, where the electrolysis of dilute sulfuric acid is taking place, would the rate of electrolysis be constant always, even at the beginning? By rate of electrolysis, I mean the ...
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Is a buffer solution really inactive beyond a range of pKa±1?

I have learnt from several books that the range of a buffer solution is always from $\ce{pH = pKa - 1}$ to $\ce{pH = pKa + 1}$. But is there any solid reason to this and any exception?
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How to prevent hydrogen embrittlement in SmCo magnet?

We have a measuring apparatus that incorporates a samarium-cobalt (SmCo) magnet. Normally this is exposed to various gases under test. However, a problem has arisen with hydrogen, namely the magnet ...
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Gibbs energy of electron transfer

the reaction Gibbs energy of a cell: $\Delta_rG^o=-nFE^o$ and the Gibbs energy of photoinduced electron transfer: $\Delta_{ET}G^o=N_A\{e[E^o(D^{+.}/D)-E^o(A/A^{-.})]+\omega(D^{+.}A^{-.})-\omega(DA)\}-\...
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How can surface excess be negative?

If we have interphase of two phases $\alpha$ (water) and $\beta$ (air), surface excess is defined as $$\Gamma_i = \frac{n_{i,\mathrm{tot}} - n_{i,\alpha} - n_{i,\beta}} A = \frac{n_{i,\mathrm{int}}} A,...
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Heat capacity at constant volume and Gibbs free energy

I want to know if it is possible to derive heat capacities, in this case, in constant volume from another thermodynamic Potential which is not the Helmholtz free energy $F$. I am aware of the ...
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Can you react dilute nitric acid and sucrose? [closed]

I've only seen information online that concentrated nitric acid can react with sucrose, but can a nitric acid solution with a molarity ranging from 3M to 5M also react with sucrose to create oxalic ...
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Why does Chloride ion get oxidized in electrolysis?

Suppose I have an NaCl solution in a beaker and I put two electrodes in the jar, the ends of which are connected to a normal AA battery (1.5V). Now, my question is, why is the following reaction ...
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Will current flow if only chloride ions are present in water? [closed]

Consider a hypothetical scenario: If I have a beaker of water, and I just put chloride ions in there and put in two electrodes that are connected to the two ends of a battery, will current flow? PS: ...
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Not able to match the number of components in a system with the "species-approach" to the Gibbs phase rule

The Gibbs' phase rule states that the number of degrees of freedom in a system $F = C - P + 2$ where $C$ are the number of components and $P$ are the number of phases. The term $C$ can be expanded to $...
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Pressure dependence of the equilibrium constant

The equilibrium constant of a chemical reaction can be calculated if the $\Delta_\mathrm rG^\circ$ is known which is a function of only temperature. So if a reaction happens inside a container ...
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Which solvent is good for using SU-8 particle in Optical tweezers?

I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
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Relation of temperature with equilibrium [closed]

In an endothermic reaction if we increase the temperature then the equillibrium shifts forward and if we decrease the temperature then equillibrium shifts backward
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Total entropy change for a spontaneous reaction

For the oxidation of iron, $$\ce{4 Fe(s) + 3 H2O(g) -> 2 Fe2O3(s) + 3 H2(g)}$$ the entropy change is $ \pu{–549.4 J K^{-1} mol^{-1}}$ at $\pu{298 K}.$ In spite of the negative entropy change of ...
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How much iron can be generated when 55g of sulphur is heated with excess iron fillings [closed]

How much iron can be generated when 55g of sulphur is heated with excess iron fillings
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Relation of temperature to effusion and diffusion

We were studying Graham's Law today and its dependence on Temperature, Pressure, Area, etc. However, our teacher said that, for diffusion: $$R \propto \sqrt T$$ and for effusion:$$R\propto1/\sqrt T$$ ...
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Problem understanding the rate of reaction of reversible reactions

Case 1: $$\ce{CH_3COOH + NaOH<=>CH_3COONa + H_2O}$$ At equilibrium, there remain extremely small concentrations of the reactants (acetic acid and sodium hydroxide), and comparatively large ...
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Why the product of ions in Kohlrausch's law [closed]

I'm having trouble wrapping my head around Kohlrausch law of infinite dilution and molar conductivities in general. Also is sum_of ion_conductivitiy * ion_concentrations (there are multiples ions so ...
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Why does methane have 4-different bond dissociation energies?

I will elaborate on my question here. In my Lecture Notes it is mentioned that for methane, there are 4 different $\text{C-H}$ bond energies. I plotted a quick graph of the bond energies to analyse ...
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Why does it seem that the heat of combustion is higher with substances of greater molecular weights?

Why does it seem that the heat of combustion is higher with substances of greater molecular weights? How do the intermolecular forces or bonds of the reactants affect the heat of combustion? I have ...
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Mass of silver iodide that dissolves in ammonia [closed]

What mass of $\ce{AgI}$ will dissolve in $\pu{1.0 L}$ of $\pu{1.0 M}$ $\ce{NH3}?$ Neglect the change in concentration of $\ce{NH3}.$ Given: $K_\mathrm{sp}(\ce{AgI}) = \pu{1.5E-16};$ $K_\mathrm{f}(\ce{[...
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Interpretation of azeotropes from statistical mechanics derivation

In an earlier posted question titled Reason for the formation of azeotropes, @porphyrin presented an elegant derivation from statistical mechanics to interpret partial pressures for the two components ...
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On the definition of eigenframe

While reading the following article, Elizaveta A. Suturina, Kevin Mason, Carlos F. G. C. Geraldes, Ilya Kuprov, David Parker, Beyond Bleaney's theory: experimental and theoretical analysis of ...
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Why all 4 bonds of CH4 can't be broken at a particular time t simultaneously? [closed]

I was studying bond enthalpy and came across the example of CH4. All 4 bonds have different bond enthalpies because we go about it like we first remove the 1st hydrogen, then 2nd and so on. But my ...
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Weird equilibrium problem [closed]

I'll try to approach the equilibrium from both sides, and see what happens. Stay with me for the ride guys! Case 1: $$\ce{NH3_{(aq)} + H2O_{(l)} <=> NH4^{+}_{(aq)} + OH^{-}_{(aq)}}$$ Let the ...
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Semi-Infinite Potential Square Well: Negative Potential

I am having trouble with a problem involving a Semi-infinite potential square well: I have written down some notes that I added to the post. I have problems understanding the physical situation. See ...
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Why are most organic molecules diamagnetic, when most of them have non-paired nucleus spins?

I was studying some coordination chemistry and somewhere around the text it was stated that one could know the magnetic moment of a complex from its metal because since all ligands were often ...
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Why is the aqueous solution of ammonia considered alkaline? [closed]

$$\ce{NH3_{(aq)} + H2O_{(l)} <=> NH4^{+}_{(aq)} + \fbox{$\ce{OH^{-}_{(aq)}}$}}$$ Now one might say, due to the presence of $\ce{OH^-}$, the aqueous solution is alkaline. But I'd like to make the ...
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How to Combine an Emission spectrum into a colour? [closed]

I am trying to wrap my head around the flame test, and for the most part, it is making sense. My question is their a way to figure out the colour of a flame of an unknown element given the emission ...
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1answer
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Dissociation of phosphorus pentachloride in gas syringe

Phosphorus pentachloride is introduced into an empty gas syringe which has a movable, tightly-f‌itting plunger. The gas is allowed to expand until equilibrium is reached at a temperature at which the ...
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Why can two wavefunctions can be interchanged in integrals involving hermitian operators?

In many textbooks, it is said that because operators in QM are hermitian, we can write: $$\int \psi^*\hat{A}\phi\,\mathrm d\tau = \int\phi^*\hat{A}\psi\,\mathrm d\tau$$ An operator $\hat{A}$ is called ...
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What are angular and radial nodes?

Nodes are the points in space around a nucleus where the probability of finding an electron is zero. However, I heard that there are two kinds of nodes, radial nodes and angular nodes. What are they ...
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How are London Dispersion Forces generated?

While talking about the gaseous state of matter we came to the topic of London Dispersion Forces caused by the generation of a dipole in one atom which induces a dipole in another. While talking about ...
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What does Partial charge means in Dipole Dipole forces [duplicate]

Dipole-dipole forces act between the molecules possessing permanent dipole. Ends of the dipoles possess “partial charges” and these charges are shown by Greek letter delta (δ). Partial charges are ...
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how dilute should the solution be for a noticeable enough colligative property such as relative lowering in vapor pressure?

I was mixing soup powder with boiling water today and noticed the vapors coming from the water suddenly vanish; seemed like the powder being non volatile decreased the mole fraction of water in the ...
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Should there be a better explanation on Van Der Waals force? [duplicate]

The explanation on how Van der Waals force forms is this: Van der Waals forces consist of induced, temporary dipoles between neighbouring molecules. These are caused by constantly shifting electron ...
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Removing Heavy Rust from Very Old Carbon Steel Carving Knife on the Cheap

I am trying to remove heavy rust from a carbon steel 10-inch carving knife. Mothers Polish did not get rid of much of the rust. I turned to vinegar soaking and scrubbing: At first it took off a good ...
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Is the wavelength of light generated through a chemical reaction independent?

The chemical reaction in question is the reaction between Luminol and hydrogen peroxide. Is the wavelength of light generated through this reaction dependent on the concentration of either reactant? I ...
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What does “efficiency” refer to for a refrigerator?

A problem from my textbook mentions a refrigerator working with $35\,\%$ efficiency. I thought that in this case the coefficient of performance (COP) was used, specifically $Q_\mathrm{cold}/W,$ which ...
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Why do we assume that the successive deprotonation of a polyprotic acid happens when only the previous deprotonation has reached equilibrium?

The steps for finding the concentration of the species at the equilibrium of polyprotic acid are as given in this book in section $10.16$ and illustrated on the next page. I have three questions, but ...
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kJ per mole or kJ per 2 moles?

From Chemguide: Here is a simple reaction between hydrogen and oxygen to make water: $$\ce{2 H2(g) + O2(g) -> 2 H2O(l)} \quad \Delta_\mathrm{r}H^\circ = \pu{572 kJ mol^-1}$$ First, notice that ...
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Will a liquid-liquid emulsion and the separated emulsion have same volume?

Let's assume that there is no dispersed gas (bubbles). Not sure about dissolved gas; maybe you can tell me if that matters. Ordinary liquids (aqueous solution and biological oil). Surfactants are ...
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What quantity is one mole in the reaction in enthalpy change? [duplicate]

For example, I have a reaction: $H_2(g)+\frac{1}{2}O_2(g)→H_2O(l),𝛥H=-285.8 kJ mol^{-1}$ What does this "per mole" in the unit represent? What quantity is one mole?
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Why is potassium less dense than sodium?

Potassium has a density of $\pu{0.86g/cm3}$ and sodium has a density of $\pu{0.97g/cm3}$,even though potassium is below sodium and one might expect the alkali metals to exhibit monotonously increasing ...
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What happens in an electrolytic cell when the cations are different from the metal of the anode?

Suppose we have an electrolytic cell with copper(II) sulphate solution as the electrolyte, and lead metal as the electrodes. Will lead ions be discharged from the anode into the solution? What will be ...
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Why is the van ’t Hoff relation an approximation?

Lately, I've been looking and thinking about the fact that a professor told us in an advanced physiology lecture. When it came to mentioning osmotic pressure and the van ’t Hoff relationship $$ \pi = ...
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Raoult's Law confusion

I have this confusion regarding the statement of Raoult's Law. It states that The partial pressure of each component of an ideal mixture of liquids is equal to the vapour pressure of the pure ...

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