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
106 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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397 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 ...
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67 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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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
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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, ...
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1answer
137 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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63 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 ...
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1answer
53 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
40 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 ...
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60 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 ...
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135 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 ...
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1answer
236 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
356 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
106 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
59 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
838 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) ...
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2answers
265 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
98 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
123 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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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
68 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 ...
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3answers
377 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 $\ce{H2+}$ ...
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1answer
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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/...
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1answer
72 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 ...
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2answers
843 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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195 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 ...
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1answer
100 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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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
121 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
80 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 ...
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1answer
98 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
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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 ...
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53 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 ...
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2answers
244 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 ...
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1answer
147 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 ...
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1answer
205 views

Find the minimum temperature at which the reaction will become spontaneous [closed]

This question came in my entrance exam and I think 273 K should be the answer because the reaction is already spontaneous. I just want to know if I've attempted it correctly. For a certain ...
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1answer
160 views

Compressibility factor of hydrogen at low pressure and constant temperature

As we all know, the compressibility factor $Z$ of hydrogen and helium is always greater than $1$ at a constant moderate temperature. But, if we look at the virial equation of compressibility factor $$...
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1answer
61 views

Why is the ROHF spin density of the propenyl radical not symmetric?

I was preparing some material for my students and in order to illustrate the concept of spin density and how the ROHF method gives a purer description of this property than the UHF method. I prepared ...
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42 views

Theoretical Calculations for Potential Generated in Salt Water Battery

I am using a $\pu{1.5 M}~\ce{KCl}$ solution as electrolyte and copper and aluminium electrodes but no salt bridge. So basically there is only one beaker with the two electrodes in it with the $\pu{1.5 ...
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1answer
66 views

Melting Point of Pure Gold [closed]

The melting point of gold was changed from 1063 deg C to 1064 deg C in an ASTM procedure that uses the melting point of gold as the end point for a test. Did the melting point change somehow or was ...
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1answer
380 views

what the solution of this problem, negative absorbance values in UV-vis spectrum

In my project, I take the UV-visible spectrum of reaction between pyridinium chlorochromate and N-acetylcysteine. In some wavelengths, the absorbance value is negative for example it is (-0.006, -0....
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337 views

Why doesn't the particle in a ring model have a potential energy term?

I was thinking of the "particle on a ring" problem as a subdivision of a bigger problem, i.e. the hydrogen atom. While in the hydrogen atom problem, the Hamiltonian contains a potential energy term, ...
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2answers
699 views

Entropy change of isothermal irreversible expansion of ideal gas [duplicate]

Two mole of an ideal gas is subjected to isothermal expansion from $\pu{2 atm}$ to $\pu{1 atm}$ at $\pu{300 K}$. Calculate entropy change of the system, surrounding and total, if the process is ...
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68 views

Adiabatic flame temperature of a blast furnace gas

Calculate the adiabatic flame temperature of combustion of a blast furnace gas analyzing $25\%$ $\ce{CO}$, $10\%$ $\ce{CO2}$, and rest nitrogen. Use theoretical amount of preheated air at $\pu{1000 °C}...
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Which solution has higher boiling point?

Between a 2% (w/v) aqueous solutions of $\ce{NaCl}$ and $\ce{RbCl}$, which will have a higher boiling point. Here there are two competing factors. First there's the fact that $\ce{NaCl}$ has a higher ...
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1answer
93 views

Determine surface area of heat exchange tube

A heat exchanger is used to cool down a stream of $\pu{20 kg s-1}$ of water from $\pu{80 °C}$ to $\pu{60 °C}$. The cooling water enters at a rate of $\pu{12 kg s-1}$ and $\ce{20 °C}$. The overall heat ...
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1answer
61 views

Why can't an electrochemical cell be a single cell? [duplicate]

If I put two electrodes of two different metals in 1 solution containing ions for both of the metals and connect these electrodes with a wire, do I still have an electrochemical cell ? Or does it have ...