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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Why is the value of $A$, in the expression for Boltzmann's distribution of speeds, not directly calculated?

I've read the proof for the expression for Boltzmann's distribution of speeds on this site. There, $f(v)$ is first factorized into $f(v_x)$, $f(v_y)$ and $f(v_z)$ and $A$ into $A_x$, $A_y$ and $A_z$. ...
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Products formed on the electrolysis of wet HF

We know that, electroysis of water produces $\ce{O2}$ at anode and $\ce{H2}$ at cathode. In a similar way I thought that on electroysis of $\ce{HF}$ it would produce $\ce{F2}$ and $\ce{H2}$ at their ...
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How to calculate the temperature of a mix?

I'm trying to solve a problem but there is something im not quite getting. It says, if we mix 84.2 mL liquid water at a 15°C and 50 mL of 100% sulfuric acid at 25°C, What is the maximum temperature ...
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How can the reaction heat be ignored in an energy balance?

I have received from my professor the following (here summarized) problem: A first-order exothermic reaction A->B takes place in a tubular reactor (typical PFR). The tube is cooled to a constant ...
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Calculating the Hopping distance in K+ F- bonds

[![enter image description here][1]][1] This is a graph showing the formation of K+ F- ionic bonds. To my understanding, when the atoms are far apart, their neutral state is more stable. But when they ...
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Definition of Molecularity of a reaction? [closed]

If nucleophilic attack occurs simultaneously at two seperate electrophilic sites of the molecule following SN2 at each site, will the moleculularity still be 2? Does molecularity depend on the total ...
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Why can't there be a gas-dispersed-in-gas colloid? [closed]

Colloids, a special type of heterogeneous mixtures, typically have two components. One is the dispersed phase (DP), which is the "solute-like" part and another one is the dispersion medium (...
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If there are two possible reactions, will the one with a more negative Gibbs Free Energy be favored?

I was thinking of the reaction between methanol (CH3OH) and sodium amide (NaNH2) and wondering if I could get methylamine (CH3NH2) from it. One reaction forms methylamine and sodium hydroxide, while ...
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Analytical Prediction of Molecular Interactions [duplicate]

Is it possible to predict the molecular interaction between any two molecules analytically or through some simulation mechanism based upon analytical theory? I see a rather big gap between, say ...
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Relation between Solubility Product and Equilibrium Constant

I had read about Solubility, and I found that Solubility is not Molarity (because previously I believe that both are same thing). But, they have a big difference (source : https://en.wikipedia.org/...
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Fractional Composition of Acid Question

I present to you a fractional composition question that my professor refuses to answer because he encourages me to use equations without understanding them. Any help you can provide would be very, ...
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For the same substance, which are stronger, the bonds in the solid or the bonds in the liquid?

As a teacher, I show students the particle model as an explanation of solids, liquids and gases, and changes of state. I did this today, explaining that the bonds in the solid break because the ...
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Standard Gibbs free energy when all the reactants and products are at standard condition

I have read in my textbook that for a reaction $\Delta G=\Delta G^o-RT\ln Q $, where $\Delta G^o$ is the Gibbs free energy change when the initial concentration of products and reactants are unity. ...
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Is the formation of nitrogen dioxide spontaneous?

I was studying Thermodynamics from my Chemistry textbook (page 181-182, section 6.6 (a)). I have a question regarding the following text from my book. Now let us examine the following reactions: $$\...
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How to prepare standard sample of benzene for gas sampling bag?

I need to make a 1 ppm gaseous standard of benzene in nitrogen gas within a Tedlar® gas sampling bag. Is this as simple as injecting 1 μL of neat benzene liquid into 1 L of nitrogen gas within the bag?...
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Reaction rate of 2 H2 + O2 → 2 H2O

I am interested in the kinetics of the reactions: $$ \begin{align} \ce{2 H2 + O2 &-> H2O}\tag{R1}\\ \ce{2 CO + O2 &-> 2 CO2}\tag{R2}\\ \end{align} $$ I looked at the NIST website hoping ...
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What will happen in the volume occupied capacity of each gas when separator is removed? [closed]

Consider a situation where two gases occupying volumes $V_1$ and $V_2$ and having partial pressures $p_1$ and $p_2$, respectively, are kept separated in a rigid container. If the separator is removed, ...
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Book reccomendations for Pertubation Theory? [duplicate]

I'm sorry if this is an inappropriate place to ask this, but I'm still trying to get the hang of this site. So my book is Thomas Engel and Philip Reid Physical Chemistry $3^{rd}$ ed. I'm on the ...
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How to identify isochoric process from the problem's wording?

Problem 19 from NEET's Solved Paper 2013: The amount of heat energy required to raise the temperature of $\pu{1 g}$ of helium at NTP from $T_1$ to $T_2$ (in kelvin) is \begin{align} &\text{(a)}~\...
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Why does the factor of ⅔ come in when we calculate net flux due to diffusion for an ideal gas

As per Atkins' Physical Chemistry (11E) Pg:694. We arrive at a crude estimate for the net flux through an imaginary flux plane. We find it to be $$J_{z}=-\frac{1}{2}v_{mean}\lambda(\frac{d\mathcal{N}}{...
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How do thermodynamic variables behave in reversible and irreversible processes?

I read this definition: reversible process is one which can be stopped at any stage and reversed so that the system and surroundings are exactly restored to their initial states. An irreversible ...
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How to find the wave equation in a 1D box with a 2 different V(x) values

So this is for a simple infinite well $1$D box. The bounds are defined as $V(x)=0$, for $0<x<\frac{L}{2}$, and $V(x)=V_0$ for $\frac{L}{2}<x<L$ with everywhere in the box having a ...
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How does 25% CO2/75% Ar welding gas exist?

What state does a 25% $\ce{CO2}$ / 75% $\ce{Ar}$ mixture exist in under high pressure? This mixture is a common welding shielding gas. I'm not sure if manufacturers are referring to this mixture by ...
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Relation between concentration and activation energy

Will increasing the concentration of the reactants in a chemical reaction increase the proportion of molecules with an energy greater than the activation energy $E_\mathrm{a}$? It seems to me that the ...
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How do we find hybridization when molecule has resonance?

Consider the following image which shows the resonance structures of $\ce{CO_3^{2-}}$ ion. What is the hybridization of $\ce{O}$? How do we proceed in such cases? In one resonance structure, the top ...
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Rate equation for the decomposition of hydrogen peroxide with iron(III) chloride as catalyst [duplicate]

I am trying to determine the activation energy of the decomposition of hydrogen peroxide with iron(III) chloride added as a catalyst. To do that, I need to find the rate constant, but I am not sure ...
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-1 votes
1 answer
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Viscosity and repulsive forces

Suppose we let a ball move in a fluid with initial velocity $u_i$. Then as time goes on its velocity goes down and tends to $0$ after infinite time. I understand viscosity in the following way: In ...
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Why is the momentum of the wave function in a 1-D particle-in-a-box = 0?

Is this implying that a particle in the box for 1-dimension has no momentum? Or is the momentum average out to $0$ on throughout the region $0\leq x\leq a$? For reference, I was told the state was $n =...
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How to calculate vapor pressure of ethanol at given temperature?

The following is a part of the problem I am struggling with. I think what I need is a vapor pressure of ethanol at $\pu{25 °C},$ but I may be totally wrong. A reactor is charged with $\pu{60 bar}$ of ...
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Energy change of isentropic expansion of ideal gas

I'm trying to get a better grasp on dealing with different processes thermodynamic, and this one is giving me trouble. The differential of energy is given by $$dU= \delta Q + \delta W~.$$ I'm ...
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Does Boltzmann distribution refers to microstates or particle's probability?

I am reading about the Boltzmann distribution and I can't grasp the following: $$p_i = e^{-\frac{E_i}{k_B T}}$$ Is this the probability finding the system at a microstate with Energy $E_i$ or the ...
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For Radiochemistry why is a recovery range of 30-110% acceptable for isotopic tracers used for alpha spectrometry analysis of radionuclides?

Just like the title says. I am right now isolating and concentrating several radionuclides from environmental samples using micro-coprecipitation to be able to analyze it on an a alpha spectrometer. ...
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1 answer
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Why do we use the ratio of Critical Pressure and Critical Temperature to calculate size of a gas molecule?

Our teacher explained that using the ratio of Critical Pressure and Critical Temperature is preferred over Critical Volume to calculate the size of a gas molecule when all these quantities are taken ...
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Enthalpy Departure

I'm trying to fill in the steps from my textbook on the derivation of enthalpy departure from ideal gas behavior. My textbook gives the variation of mass-specific enthalpy with temperature pressure as ...
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Heat capacity of solution = Solute + Solvent?

Is the heat capacity of a solution the sum of the heat capacities of the solvent and the solute? Based on what I have learned, specific heat is determined by the interaction between molecules. This ...
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Derivation of the Equation $p=\rho^2 (\partial F_s/\partial \rho)_T$

I'm trying to derive a relationship between the mass-specific Helmholtz free energy,the pressure, the temperature, and the mass density. It is given by $$p=\rho ^2\left ( \frac{\partial F_s}{\partial \...
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Why is there a large increase in volume when an alkali metal is dissolved in liquid ammonia?

My teacher said unexplainedly that when alkali metals dissolves in liquid ammonia, there is a large increase in the volume. I found a paper that confirms this fact [1]: In the course of recent ...
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Free induction decay acquisition in NMR

Recently, there was an interesting Q&A exchange on free induction decay acquisition in NMR Is intensity in NMR spectra acquired at regular time intervals? with useful answers. I have not acquired ...
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Faradic and non-Faradic current in Voltammetry

Below is a schematic drawing for a three-electrode cell used for cyclic voltammetry: Image modified from Wikipedia Voltammetry This is what I understand with the voltammetry working principle from ...
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Are there any papers illustrating carboxylic acids displaying J-coupling of CH to the OH protons?

I understand that ethanol will display a J-coupling to the OH proton if observed in the absence of water, but are there any papers showing how to find this J-coupling (a 3-bond H-H J-coupling between $...
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Enthalpy contribution and heat capacity

Imagine having at the input of a burner 105 mol/h of $\ce{O_2}$ at 50 °C. The enthalpy contribution of this input mass is calculated using the Kirchhoff equation $$\Delta H = \Delta H^° + \int_{25 °C}^...
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Density gradient vs. entropy of mixing

I was wondering how real gases would behave when they are released into a closed container with fixed volume. For example, suppose we use chlorine and nitrogen gas. Obviously, chlorine has a higher ...
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Will Lithium displace a sodium salt?

This question is based on a discrepancy I have observed in my limited knowledge about the reactivity and electrochemical series. In the reactivity series it is mentioned that Na>Li in reactivity ...
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Why 3 and not 6 in U = 3/2RT from the equation for the internal energy of an ideal gas?

Internal energy of an ideal monatomic gas is $$U=\frac{3}{2}RT.\tag{1}$$ While I understand the derivation, I do not understand why we multiply by $3$ rather than by $6.$ According to Khan Academy ...
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Tight-binding model in the presence of a metal atom

Consider a molecule such as a porphyrin ring. For many purposes, a simple tight-binding model in which only pi-electrons are included provide a very good description of the electronic levels, shape of ...
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Doesn't the eutectic diagram violate Gibbs's phase rule?

EDIT: As the question hasn't attracted any answers, I tried to put in more detail. Gibbs's phase rule for a 2 component system at constant pressure says that $F=3-P$, i.e., that the number of degrees ...
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Aren't electrophilic addition reactions of alkenes also nucleophilic addition reactions?

And if they are nucleophilic substitution reactions as well, then why do we not call them "electrophilic and nucleophilic addition reactions of alkenes"? Consider the reaction between ethene ...
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1 answer
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Finding the reaction order from a given plot of chemical kinetics

What will be the order of the reaction for a chemical change having $\log t_{1/2}$ VS $\log a$ Where $a=$ Initial concentration of reactant and $t_{1/2} =$ Half Life? 0 order 1st order 2nd order None ...
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3 votes
3 answers
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How can a 90 degree pulse cause precession perpendicular to the applied field in proton NMR

From my understanding, a proton's magnetic moment in an NMR experiment can undergo precession in only two discrete states: either parallel to the applied magnetic field, or antiparallel to it. ...
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3 votes
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If a = 0 for a Van der Waals gas, what does that signify?

I know that if $a = 0$ for a gas at certain temperature and pressure, it means that the molecules of gas have almost no attractive forces acting between them. But does that also mean that the ...
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