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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1answer
230 views

How dependent is the molal depression constant on the nature of solute?

I've been reading about the molal depression constant (freezing point depression constant) for binary solutions in class. I encountered a problem (see below) in which the constant $K_f$ was to be ...
2
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2answers
403 views

Gibbs free energy in standard state vs. equilibrium

I have a problem with the definition of the standard Gibbs energy and its connection to the equilibrium constants. I think, that I've basically understood what the different equation mean but there ...
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0answers
228 views

Conversion of graphite into diamond [duplicate]

The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively. The conversion of graphite [C(...
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1answer
126 views

Is there a error at page 566 of Atkins Physical Chemistry? [closed]

At page 556 I found this question being analyzed and the rate law is provided. However, when I apply steady state approximation, I can't find the result without the factor 2. Is it me being wrong?
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2answers
87 views

Ionic equilibrium between multiple ions

This is a question from IIT-JEE 1993: For the reaction $$\ce{[Ag(CN)2]^- -> Ag^+ + 2CN^-}$$ the equilibrium constant at $\pu{298 K}$ is $\pu{4e-10}$. The silver ion concentration in a ...
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1answer
128 views

What could cause a peak to split into 2 resonances as temperature increases in NMR spectroscopy

I understand that some peaks may coalesce upon an increase in temperature due to an increase in free rotation, this does occur with some peaks in my data. Why might you see a peak split into two other ...
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214 views

What is the largest coupled cluster calculation that has ever been done (as of March 2019)?

I am doing some research and trying to make sure the numbers I am reporting are accurate. I found that the paper by Sylvetsky et. al. says:[1] We were, however, able to complete a ...
5
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1answer
148 views

Energy of photons of given frequency and number

I’m having trouble with calculating the energy of $\pu{5.00e10}$ photons of frequency $\pu{1.00e9 s-1}$. I know that to calculate the energy $E = hf$ is to be used. However, I am unaware as to what ...
5
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4answers
749 views

Why does the degree of dissociation change when we dilute a weak acid even though the equilibrium constant $K$ is constant?

$K$ represents the ratio of concentrations of molecules in a solution at equilibrium, which means that $Q_\mathrm{r}$ (that ratio at any given point) looks to be identical to $K$. In other words, the ...
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1answer
3k views

What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state?

When an electron in a higher energy state jumps to a lower energy state in Bohr’s model of hydrogen atom, it emits a photon which has energy equal to the difference in the energy between the final and ...
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1answer
24 views

Overall enthalpy balance on a mixing process

Let's say I have a mixing process involving $\ce{A}$ and $\ce{B}$ at temperatures $T_\ce{A}$ and $T_\ce{B}$, respectively. The $\ce{AB}$ mix is at temperature $T_p$. Our $ΔH_\mathrm{mix}$ is defined ...
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2answers
136 views

Feasibility and Entropy

Suppose you've got some reaction that has a positive $\Delta H$, and also has positive $\Delta S_\mathrm{sys}$. Due to the equation $$\Delta S_\mathrm{tot} = \Delta S_\mathrm{sys} - \frac{\Delta H}{T}$...
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1answer
136 views

if a balloon full of warm air was placed in a refrigerator, what is the result? [closed]

If a balloon full of warm air was placed in a refrigerator, What will happen to the Ballon ?
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2answers
401 views

What is a good source for large tables on the properties of water?

I'm currently doing an investigation for school on finding the Clausius-Clapeyron relation/gradient for boiling water and comparing it to the gradients along my line of best fit. It is given by the ...
3
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1answer
69 views

Minimizing energy of a molecule

I am minimizing energy of butane on the CHARMM Force Field and I am confused on how to go about getting a uniform unit for each different PE as in the potential energy for bond, angle, torsion, VDW, ...
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0answers
125 views

How to calculate the cell potential after the reaction has operated long enough for the Fe2+ to have changed by some concentration?

Consider the cell described below at $\pu{261 K}$: $$\ce{Fe | Fe^2+ (\pu{0.925 M}) || Cd^2+ (\pu{0.981 M}) | Cd}$$ Given $E^\circ_\ce{Cd^2+ -> Cd} = \pu{-0.403 V}$, $E^\circ_\ce{Fe^2+ -&...
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1answer
65 views

Polyprotic Acid Titrations

Titrating a mixture of strong and weak acids will yield endpoints such that the volume of base required to reach each endpoint will be different for each acid, e.g. in a mixture of HCl and CH3COOH, ...
2
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1answer
165 views

Determining the reduction potential of a half cell reaction at a given pH

$E^\circ_\ce{Cu^2+|Cu} = \pu{0.34 V}$. What will be reduction potential at $\mathrm{pH} = 14$ for the same couple? Given that $K_\mathrm{sp}$ of $\ce{Cu(OH)2}$ is $10^{-19}$. My Attempt I think ...
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0answers
65 views

AP Chem Question about Reaction Rate - Confused?

I found this question in the AP Chem book, and I understand why B is the answer (as the answer key says). However, I don't understand why D is not also correct. The question is: A multistep reaction ...
2
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1answer
99 views

Cobalt electroplating over nickel-plated steel

From my research, I understand that cobalt can be used on top of a nickel layer to improve durability of the nickel plating on a steel object. I am using a nickel anode and nickel acetate as ...
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4answers
3k views

Why does liquid water form when we exhale on a mirror?

In the descriptions below, I always assume external pressure to be constant at 1 atm, the condition where daily observations are made. 1) When I exhale on a mirror, liquid water forms on the mirror. ...
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1answer
41 views

Why do reactions happen at all? [closed]

What makes some atoms/compounds reactive and some noble? What is the fundamental truth behind a reaction? It seems that two species can undergo number of combination to give a compound. Say Sodium and ...
2
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1answer
95 views

Shortcut method to find atomic term symbols ignoring the spin orbit coupling

Is there any shortcut method by which we can find the atomic term symbols ignoring the spin-orbit coupling, i.e. ignoring the values of J. For instance, when writing the d-d transitions for any ...
5
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0answers
226 views

Helmholtz double layer

I don't quite understand what is meant by the Helmholtz double layer. Textbooks states something along the lines of: the colloidal particles attain charge by selective adsorption, due to this it ...
0
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1answer
391 views

Why does the colour of gold sol change with particle size? [duplicate]

Regarding the colour of gold sol, my book says Finest gold sol is red in colour; as the size of particles increases, it appears purple, then blue and finally golden. This is the image I found on ...
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2answers
632 views

The respective speed of five molecules are 2, 1.5, 1.6, 1.6 and 1.2 km/s. The most probable speed in km/s will be?

The respective speed of five molecules are 2, 1.5, 1.6, 1.6 and 1.2 km/s. The most probable speed in km/s will be? 1. 2 2. 1.58 3. 1.6 4. 1.31 I think the answer should be 1.6 km/h but the ...
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1answer
154 views

Determination of pKb of a mono acidic base

$20$ mL of a weak monoacidic base($\text{BOH}$) requires $12$ mL of $0.3$ M $\text{HCl}$ solution for the equivalence point. During titration, the pH of the base solution was $10$ upon the addition of ...
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1answer
76 views

How do salt additives and impurities affect a critical micelle concentration?

So I understand that a CMC typically decreases as more salt additives are added. What I am not clear on is how exactly. The head groups are charged in this example (one anionic and one cationic) so ...
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1answer
1k views

Relation between electron gain enthalpy and electron affinity

The correct relation between electron gain enthalpy $(Δ_\mathrm{eg}H)$ and electron affinity $A_\mathrm{e}$ at any temperature '$T$' is A) $Δ_\mathrm{eg}H = -A_\mathrm{e} - \frac{5}{2}RT$ B) ...
4
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2answers
430 views

Lagrange Multipliers for the derivation of Maxwell-Boltzmann distribution

When deriving the MB-Distribution while taking the number of quantum states $g_j$ into account, the final equation I'd have to solve would be: $$\ln(g_j)-\ln(n_j)+\alpha+\beta\cdot E_j=0$$ Where $n_j$ ...
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2answers
142 views

Why is the rate of reaction calculated as d[A]/dt?

For example, for a simple chemical reaction like $$\ce{A -> C}$$ the rate of the reaction could be calculated as the rate of appearance of $\ce{C}$ or the disappearance of $\ce{A}$, which makes ...
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2answers
139 views

How to determine steady state of multi-step reaction with both reversible and irreversible steps?

I am trying to determine the relative concentrations of $\ce{U1}$, $\ce{U2}$, and $\ce{E}$ when the following reaction is at steady state. Note that $k_t$ is the zero order rate constant of new $\ce{...
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1answer
31 views

What is the velocity of de Broglie wave?

Here is my calculation: note: $ν$ – frequency, $V$ – velocity of wave, $v'$– velocity of object. $$ \begin{align} λ &= h/mv' \tag{1}\\ mc^2/h &= ν \tag{2}\\ λν &= V \quad \text{(wave ...
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1answer
80 views

What are the effects of salt additives and impurities on the CMC? [closed]

I understand what a critical micelle concentration (CMC) is, however I do not know why or how impurities or salt additives affect it when measured in specific ways. Any help is much appreciated. So ...
6
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3answers
460 views

Linear Combination of Atomic Orbitals

In Atkins Physical Chemistry 10th edition in chapter number 10B it is given that within the Born-Oppenheimer approximation, the Schrödinger equation can be solved for the molecular species $\ce{H2+}$ ...
4
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1answer
42 views

XAS spectroscopy - Differences in magnitude of 2p SOC and 3d SOC?

Within L-edge x-ray absorption spectroscopy, the spin-orbit coupling within the 2p shell results in the splitting of the L edge into L3 and L2 edges.As given in the following paper http://dx.doi.org/...
0
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1answer
81 views

Subscript on Orbitals [closed]

What do the subscripts on the orbitals (such as px, py, pzetc) mean and how can one derive these or at least gain a fundamental understanding of each? Do they describe the geometry of the shape? And ...
8
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2answers
848 views

Why proton concentration is divided by 10⁻⁷?

I am reviewing the book Biochemistry Concepts and Connections by Appling, Cahill, and Mathews and I cannot understand why they divide by the hydrogen concentration by $10^{-7}$. Why not just leave it ...
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2answers
214 views

Why is the Maxwell–Boltzmann formula inapplicable at low temperatures?

This Wikipedia article states that at sufficiently low temperatures (or high pressure), quantum effects lead to a breakdown of Maxwell–Boltzmann statistics. I know that the spacing of energy levels ...
3
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1answer
101 views

Why we should concern with A∞?

To determine the order of one reactant at pseudo concentration of another reactant the plot of $\ln(A_t - A_∞)$ versus $t$ is used. $A_t$ is absorbance of the intermediate at time $t$. $A_∞$ is ...
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0answers
49 views

Defining the partial pressure equilibrium concentration

First off, I am not a chemist. I'm an engineer with an interest in thermodynamics for engine simulation for the basis of emissions. So if I have asked something stupid, this will be why. So I am ...
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1answer
34 views

Requesting clarification on specific gravity [closed]

I am unclear why the ratio of molecular weights will yield the specific gravity of a substance relative to the standard substance (usually air or water at a specific T and P). I always took specific ...
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2answers
150 views

Denominator in rate law?

What the possible rate laws are for the decomposition of nitramide by the following process: $$ \begin{align} \ce{O2NNH2(aq) &<=>[$k_1$][$k_{-1}$] O2NNH-(aq) + H+(aq)} &\quad &\...
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1answer
44 views

What is a good resource for learning about the intermolecular bonding in water beyond high school? [closed]

I'm writing a paper for school on boiling water at various temperatures and pressures, but only noting cases wherein high temperatures were achieved without boiling under low pressure (metastable ...
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1answer
112 views

Solving a quadratic of for pressure of real gas with unknown volume

I had this question on my test: Calculate the pressure exerted (in atm) by 1 mole of $\ce{CH4}$ gas at a temperature of $\dfrac{24}{0.0821}$ K if volume occupied by $\ce{CH4}$ molecules ...
2
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1answer
115 views

Determining reaction order in equilibrium reactions [closed]

Am hoping that someone can help me with the below question, and that I am asking in the right place. Am new here, so please forgive any missteps. Given a reaction like this: $$\ce{A + B <=> C +...
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1answer
89 views

How does refrigerator actually work?

In refrigerator, heat energy got extracted from cold sink and dumped into hot source. This is not spontaneous so work must be done. I came across the following while reading a textbook: For ...
3
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0answers
56 views

Why can we know a materials properties by knowing its ground state at 0K - DFT

I have had this doubt ever since I was introduced to DFT. For what I gathered whatever results you obtained with DFT (by using VASP, quantum expresso or any other software) you can say those ...
8
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2answers
257 views

Calculating the strength of an ionic bond that contains poly-atomic ions

So the bond association enthalpy for ionic compounds like $\ce{NaCl}$ and $\ce{NaBr}$ can be easily calculated from a Born-Haber cycle. But the way a Born-Haber cycle is constructed it uses info that ...
5
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1answer
187 views

What happens to the first ionization potential when a hydrogen-like atom captures a particle?

This is a textbook problem from Resonance DLPD Physical Chemistry, Page #83: The mass of a proton is $1836$ times the mass of an electron. If a subatomic particle of mass $207$ times the mass of an ...