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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Equilibrium Problem Involving Solids: Faulty?

I am convinced that this is a faulty problem: $\ce{2 Cu + S -> Cu2S}$ For the reaction above, $\Delta H$, $\Delta S$, and $\Delta G$ are all negative. Which of the substances would ...
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2k views

Which of the following pairs show common ion effect?

Which of the following pairs show common ion effect? $\ce{BaCl2}$,$\ce{Ba(NO3)2}$ $\ce{NaCl}$, $\ce{HCl}$ $\ce{NH4OH}$,$\ce{NH4Cl}$ $\ce{NaOH}$, $\ce{NaCl}$ Its not (1) because they ...
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764 views

Balancing molecular and net ionic equations for reactions

Source:'Chemistry: The Central Science 11th edition' by Brown. Ch.4, 4.53: Question: Write balanced molecular and net ionic equations for the reactions of: chromium with hydrobromic acid; ...
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85 views

Concentration of NaIO3 using hypo

$$\ce{2NaIO3 + 5NaHSO3 -> 3NaHSO4 + H2O + I2 + Na2SO4}$$ $\mathrm{20ml}$ of $\ce{NaIO3}$ solution reacted with excess $\ce{NaHSO3}$ releasing $\ce{I2}$ that can oxidize $\mathrm{20ml}$ of $\...
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479 views

Preparation of ferric hydroxide sol

I have read that before the preparation of ferric hydroxide sol, the beaker must be cleaned by the steaming out process, while it is not necessary for starch sol. Why is that?
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27 views

Solvation rates of crystalline and noncrystalline materials

Assuming equal surface area (and other variables), would a highly ordered crystal of some substance dissolve more slowly or quickly than (or at the same rate as) a disordered sample of the same ...
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89 views

Why isn't Graham's Law working here?

In graham's law of diffusion most numericals I have seen assumes the formula $$\frac{r_1}{r_2}=\frac{P_1}{P_2}\sqrt{ \frac {M_2}{M_1}}$$ Where they say $P_1,P_2$ are the partial pressures of the ...
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217 views

Active mass,Pressure and concentration

The concentration is connected to the activity via $$a(\ce{A})= \gamma_{c,\ce{A}}\cdot{}\frac{c(\ce{A})}{c^\circ},$$ where the standard concentration is $c^\circ = 1\:\mathrm{mol/L}$. At reasonable ...
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606 views

What are some factors that influence the voltage of voltaic/galvanic cells and why?

Question: (2014 USNCO local exam Q#41): What types of changes would increase the voltage of a voltaic cell. I have learned a bit about voltaic cells, but I haven't been able to find information ...
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414 views

Calculating the wavelength of an emitted photon of a Ne^9+ ion

I'm supposed to calculate the wavelength of an emitted photon going from the 6p orbital to the 2s orbital. The first part of this problem will be to use the equation $$E=-{Rh\over n^2}$$ in order ...
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106 views

Quantum Numbers

Why are the Lanthaide (atomic #'s 57-71) elements in period 6, but in terms of electron configuration, are assigned the principal quantum number of 4? Why are certain subshells assigned quantum ...
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252 views

Difference between starch surfactant and CTAB, SDS, Tx-100

I am doing a research on the effect of surfactant on ZnO nanoparticles properties. There is a confusion here between starch surfactant and CTAB, Tx-100 and SDS. I need point on what is the difference ...
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59 views

How to minimize surface adsorption by choice of material?

I need to do buoyancy experiments in vapours consisting of organic molecules in air using a microbalance. This involves measuring the change in weight of a sealed glass sphere when exposed to the gas. ...
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111 views

Have Mossbauer spectroscopy on 67Zn ever been used to study Zinc containing enzymes?

Have Mossbauer spectroscopy with 67Zn as absorber and 67Ga as emitter ever been used to study zinc containing enzymes? The perfect answer will contain link to article/book where example of 67Zn usage ...
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121 views

Titration of alpha-amino acid with strong base

Question: $\mathrm{50~ml}$ of the conjugate acid $\ce{H3N+CH(R)COOH}$ of an $\alpha$-amino acid required $\mathrm{30~ml}$ of $\mathrm{0.1~M}~\ce{NaOH}$ to completely convert into the dipolar ion $\ce{...
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1k views

O-N-O bond angles in oxides of nitrogen

If we look at the bond angles of O-N-O in figure (c), (D) and (F), there not too much change in bond angle. Even though they are notable. So my question is, Why do we observe very small change in ...
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32 views

Is there a specific chemical property or concept that explains/predicts the triboelectric series?

Is there a chemical property (perhaps electron affinity?) that can be used to predict where a substance would fall in a triboelectric series such as this one? Or would the cause of the charge ...
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73 views

Oil refinery - How many plates are needed for a 10 degrees difference in temperature?

I am having some trouble going about this question. My first thought is to set up an ASTM separation equation to figure out the difference, but I do not know how to incorporate the reflux ratio which ...
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33 views

Computing initial reaction speed given reaction constant

Problem: $\ce{N2O}$ falls apart in oxygen gas and nitrogen gas according to a first order reaction rate. If you know that the rate constant is $0.38\ \mathrm{s^{-1}}$ at $760\ \mathrm{^\circ C}$, ...
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235 views

Interaction between soy milk and coffee producing bubbles

I noticed when I poured my soy milk (which I shook as per the directions on the carton) into my coffee, a large number of very fine bubbles rose to the surface. What causes this? Is there a chemical ...
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2k views

Relationship between Equivalence Ratio and Adiabatic Flame Temperature for Fuel Rich Combustion

I'm reading a combustion text and would like help interpreting the following passage (diagram attached). It is regarding the relationship between equivalence ratio and adiabatic flame temperature: ...
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275 views

Are forming coins starting with sodium chloride possible without the clay melting from the molten metal?

Is forming metal coins (specifically ones with copper, nickel, and zinc) possible with these steps: Carve a sheet of sodium chloride so that it is big but not too big and so that the design sticks ...
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797 views

Structure of fluoroalkylsilane

I want to use FAS (fluoroalkylsilane) in my molecular dynamics study. How can I find it's real structure? So that I can find proper forcefield for simulating the molecule. It would be very nice if you ...
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398 views

How do I measure the density of a cellulose acetate membrane?

I've been playing around with filtration methods, and got my hands on a casting machine for this purpose. My first mission was to find out how porosity can affect filtration. To see this for myself, ...
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238 views

Graph theory, isomer enumeration and chemical graph theory

Where could we find a good description of graph theory applied to the general problem of isomer enumeration and chemical graph theory?
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101 views

Making a reasonable slab of alpha quartz

I want to perform a molecular dynamics simulation with alpha-quartz as my mineral surface. I want to study adsorption of water on alpha-quartz. The most dominant error that I came up with is the ...
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113 views

Why does confinement of quantum dots result in discrete energy levels?

I'm doing a project with lead (II) sulfide quantum dots because they have optical transitions in the near infrared. I understand the simple "particle in a box" approach where confinement strengthens ...
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1k views

Magnetic moment of coordination complexes?

To understand the commonly quoted magnetic values of coordination complexes (central ion) we use $$m_l=\sqrt{n(n+2)} \text{BM where BM}=\frac{e\hbar}{2m_e}\text{JT}^{-1}$$ $n$=number of unpaired ...
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84 views

Reference to find dielectric constants and dielectric relaxation time

I am working on a Master degree and need to know the following data : The static (low frequency) dielectric constant of isopropanol at 25 °C The Optical (high frequency) dielectric constant of ...
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1answer
121 views

Is every substance in equilibrium with its vapours?

In one of my previous questions, I got an answer from user Jan: The smell of a compound as we perceive it usually depends on which receptors in the nose will bind the molecule (or not). These ...
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1answer
508 views

pKa of Tris corrected for ionic strength

I have a question regarding the molar fraction calculation of Tris buffer at different temperatures. Tris dissociates according to the following equation: $$\ce{Tris + H2O -> Tris+ + OH-}$$ So, ...
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31 views

What does “orthorhombic” actually mean?

I'm trying to understand what it means for a molecule to have orthorhombic symmetry. According to Di Lauro's "Rotational Structure in Molecular Infrared Spectra," a molecule is orthorhombic if the ...
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37 views

Number of states of phase space of a particle under Heisenberg certainty

In classical mechanics, the state of a motion can be determined by its position r and momentum p. One-dimensional motion of a particle that can be described by a trajectory in the plane that has $x$ ...
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1answer
58 views

Units of the rate constant for reactions whose order is greater than 1

In many textbooks, it is written that: The value of rate constant depends on the nature of the reactants, temperature and catalyst. It is independent of the concentration of the reactants. However,...
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31 views

Why is the iron inter-system crossing non-negligible at high temperatures?

Inter-system crossing (ISC) is a radiationless process involving forbidden transitions between singlet and triplet state. These are more common with heavy atom molecules, so I understand that ISC is ...
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37 views

What is the degree of freedom of the calcium carbonate dissociation reaction?

Question $\ce{CaCO3}$ dissociated in a closed system according to the reaction: $$\ce{CaCO3(s) -> CaO(s) + CO2(g)}$$ Assuming the reaction is in thermodynamic equilibrium, what is/are ...
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42 views

Calculating thermodynamic quantities for hydrogenation of iron nitride

HW#6.3 If the reaction $$\ce{Fe2N(s) + 3/2 H2(g) <=> 2 Fe(s) + NH3(g)}$$ comes to an equilibrium at a total pressure of $\pu{1 bar},$ analysis of the gas shows that at $\pu{700 K}$ ...
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26 views

Measuring change in concentration of hydrogen peroxide

I am conducting an experiment to find the rate constant of the decomposition of hydrogen peroxide, $\ce{H2O2}.$ For this, I was planning on using the integrated rate law: $$\ln(\text{final ...
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9 views

Lattice Energy of MX2 type

While finding the solution to the question that which among BaO and BaCl2 has hi that is energy I found that it was BaO whose lattice energy is high and there were explaining it just with charges. So ...
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20 views

Gibbs free energy calculation for redox reaction

I was wondering if it is correct to calculate the Gibbs free energy of reaction at $P = \pu{1 atm}$ and $T = \pu{1100 K}$ using the NIST-JANAF thermochemical tables. For example, for the reaction of ...
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45 views

Why is the y intercept of a G vs X curve treated as chemical potential?

Whenever I am to prove the fact that the $y$ intercept to the $G$ vs $X$ curve is basically my chemical potential, there are two equations that need to be assumed. One is $$G=\mu _{A}X_{A}+\mu _{B}X_{...
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23 views

What is the equation that describes the variation in concentration of an inhibitor in an heterogeneous catalysis?

I find myself in quite a pinch: I have to sustain a Chemical Physics exam, and I know for a fact that the professor often asks this particular question: Suppose that we have both a reacting species ...
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32 views

Arrhenius equation using concentration

I've been conducting some experiments to determine the temperature dependence of a reaction. To do this, I've been conducting the experiments at different temperatures and generated a graph of $\ln{[\...
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70 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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56 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 ...
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39 views

What will be the form of coulomb and exchange operators for electron m in an n-electron molecule?

I know that the Fock operator for electron $m$ in $n$-electron molecule would be: $$\hat{f}\!(m)u_i(m) = \varepsilon_iu_i(m)$$ $$\hat{f}\!(m) \equiv -\frac 1 2 ∇_m^2 - \sum_α\frac{Z_α}{r_{ma}} + \...
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35 views

Reaction Mechanism with a Rate Determining Step

Just a quick question on how to deal with multiple intermediaries in a proposed reaction mechanism. Here is the overall reaction: $$\ce{I-(aq) + OCl-(aq) -> IO-(aq) + Cl-(aq)}$$ Here is the ...
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23 views

Saturation dissolved oxygen level at pressure

The saturation level of dissolved oxygen in contact with a moist atmosphere is $$c = 0.21(p_\mathrm{atm} - p_\mathrm{vap}) K_\mathrm{H} M$$ where the $p_\mathrm{atm}$ and $p_\mathrm{vap}$ are the ...
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138 views

Degree of Hardness Numerical

To remove the temporary hardness from $5\ \mathrm L$ of $\ce{H2O}$ $5.6\ \mathrm{mg}$ of lime is required. Calculate the degree of hardness due to $\ce{Ca(HCO3)2}$ present in water. My attempt: $$ \...
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48 views

Free induction decay in NMR (as stated in Pavia)

There is a statement in a very popular textbook of spectroscopy by Pavia (Chapter 3, Intro. to Spectroscopy), it says "The observed FID is actually an interference signal between the radiofrequency ...