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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30 views

Raman scattering and “electron and proton center” of molecule

I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled The Raman Scattering Process, the author says the following: Light ...
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27 views

Contradiction in variation of conductance and conductivity on dilution

I do conceptually understand that on dilution conductivity decreases and conductance increases but if we look at the formula of conductivity, a contradiction seems to arise. $$\kappa=GG^*$$ where $\...
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38 views

Entropy change of surroundings and system

The entropy change of the surroundings can be calculated by the equation $dS_{sur}=\frac{dq}{T_{sur}}$ regardless of the path (irreversible or reversible). The argument is that because the ...
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1answer
105 views

Fundamentals of mathematics and physics for physical chemistry [closed]

Before I start studying chemistry, I want to gain some knowledge about the fundamentals of mathematics and physics that are important to better understand the principles of physical chemistry, ...
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Rate and heat of combustion of wood shavings and sawdust

The heat of combustion of wood shavings is more than that of sawdust. It is due to the fact the air doesn't mix uniformly in case of saw dust when it is in loose heap due to which at some part of the ...
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2answers
242 views

What is the correct pH value of weak and strong alkalis? [closed]

In the book titled fundamental chemistry for Cambridge O level, it states at page 149, Ammonia solution with a pH of 11.1 is a weak alkali and that's why it shows much lower conductivity of 0.50 ...
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640 views

Boiling point of oxygen

I am studying chemistry from the book titled "Fundamental Chemistry for Cambridge O Level" written by Rosemarie Gallagher and Paul Ingram. On page 17, it states that oxygen boils at −219 °C and ...
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45 views

Calculating Gibbs free energy for the reaction of burning methanol

Calculate $Δ_\mathrm{r}G^\circ$ for the following reaction: $$\ce{2 CH3OH(l) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)}$$ using $Δ_\mathrm{r}H^\circ$ and $Δ_\mathrm{r}S^\circ$ at $\pu{298.13 K}$ $(...
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48 views

Can a catalyst appear in the rate equation? [duplicate]

According to Wikipedia: Chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-...
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29 views

How is the value of n calculated in the Nernst equation?

I'm just not quite sure how the value is found. I know it is the number of electrons in moles that are transferred in the equation but I'm struggling to understand more complex examples. For example, ...
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51 views

Calculating ratio of conjugate base and acid when pH and pKa are given

Buffer solutions are used by biological mammalian systems to maintain the $\mathrm{pH}$ of blood plasma within a narrow range. In these systems, the compound from which this solution is obtained is $\...
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49 views

Why are pressure or volume not able to change the equilibrium constant? [duplicate]

It is stated in my textbook that temperature is the only factor that can change the equilibrium constant. According to the Ideal Gas Law, temperature is dependent on the pressure and volume. Thus, ...
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43 views

How to find the number of valence electrons with the help pf quantum numbers? [closed]

I'm bit confused on how to find the number of valence electrons. For example, Boron ($\ce{B) has the electronic configuration as: $\mathrm{1s^2 2s^2 2p^1}$. So what would be its number of valence ...
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How to boost conversion of one reactant alone in an equilibrium limited reaction?

Let us say I have two equilibrium limited reactions in a reactor, A+B =C and A+D=E. It is reported that equilibrium conversion of 1st and 2nd reaction is 80%. However, I do not want A to exit the ...
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How to boost conversion of one reactant alone in an equilibrium limited reaction? [duplicate]

Let us say I have two equilibrium limited reactions in a reactor, A+B =C and A+D=E. It is reported that equilibrium conversion of 1st and 2nd reaction is 80%. However, I do not want A to exit the ...
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1answer
60 views

Why do azeotropes boil at constant temperature? [closed]

As given in the Wikipedia page, An azeotrope (/əˈziːəˌtroʊp/) or a constant boiling point mixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple ...
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19 views

How does adding non volatile solute to a solvent lowers vapour pressure if its is independent of surface area? [duplicate]

Doubt " Relative lowering of Vapour pressure: This is due to the fact that the solute particles occupy a certain surface area and reduces area available of evaporation " If vapour pressure is ...
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49 views

Symmetry Adapted molecular orbitals of Formaldehyde

I am currently trying to find the Symmetry Adapted linear Combinations (SALCs) of Formaldehyde $\ce{H2C=O}$, and use the 1s orbitals on the hydrogen atoms, and 2s, 2px, 2py and 2pz orbitals on the ...
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2answers
37 views

In a double displacement reaction, why don’t the two products reform after being dissolved in water? [duplicate]

Let’s say I have $\ce{AB (aq) + CD (aq) —> AD + CB}$. When AB and CD are dissolved in water, they get dissociated into their component ions. But why don’t they reform as AB and CD, if it is already ...
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33 views

Is osmotic pressure different from normal pressure?

We know that when a liquid solution separated from the solvent by some semipermeable membrane, then the liquid flows from solvent to solution, and also a concentrated solution exerts more pressure ...
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1answer
57 views

Clausius–Clapeyron equation: shape of phase diagrams makes no sense

I am trying to model the melting point of a substance at varying pressures (ranging from very small to very very large). All I am trying to do is make an equation that relates melting temperature to ...
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Calculating pH dibasic mixtures of buffer solutions

Q) Calculate the pH of a solution made by mixing 0.1 M NH₃, and 0.1 M (NH₄)₂SO₄,- (pKb, of NH₃= 4.76) Here's the solution: It is a basic buffer. [Base] $$ \begin{aligned} [\text { Base }] =&\...
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29 views

Open source for atomic spectra raw data

Is anyone aware of a open source atomic spectra database? In particular I am looking for high resolution Na atomic emission which can be downloaded in csv or Excel. I am aware of NIST but I could not ...
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2answers
62 views

Why do things want to lower their energy? [closed]

Like if we consider a container of gas molecules as a system, Why does it want to lower its energy? I have read that always more spontaneous events are favored. So Gibb's Free energy should have a ...
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3answers
50 views

Ideal Gas equation and its Assumptions [duplicate]

The two assumptions are that the gases are points of mass that move, they have no volume and that there is no interaction between other molecules. But even the points of mass can collide with each ...
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2answers
25 views

Does an increase in pressure always causes increase in molar concentration of each gaseous substance involved?

Question Statement : "An increase in pressure (caused by decrease im volume) at equilibrium results in increase in molar concentration of each gaseous susbstance involved" This statement is given ...
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83 views

Quantization of particle on a sphere

While studying particle on a sphere, I read that boundary condition on $\theta$ and $\phi$ results in quantization. I understand boundary condition for $\phi$ part which varies from 0 to 2$\pi$. As $\...
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1answer
65 views

How is Raoult's law a special case of Henry's law and not vice versa?

I know that Raoult's law can be a special case of Henry's law when the value of the Henry's constant becomes equal to the vapour pressure of the pure state of the liquid. Why can't we say the opposite,...
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2answers
46 views

What is the relationship between entropy and heat capacity?

The molar heat capacity of hydrogen gas and deuterium gas are nearly the same, 28.8 J/K mol and 29.2 J/K mol respectively, but the absolute entropy of deuterium (145.0 J/K mol) is significantly larger ...
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1answer
24 views

Limiting the minimum percentage of oxygen in atmosphere maintained by an oxygen absorber / scavenger?

I'm aware that oxygen in the atmosphere of a sealed package can be readily removed by using oxygen absorber/scavenger such as granulated iron and sodium chloride but my understanding is that these ...
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4answers
129 views

Calculation of Degree of Dissociation from Ostwald's Dilution Law

A "weak" electrolyte, $\ce{A+B-}$, ionizes in solution as: $$\ce{AB <=> A+ + B-}\tag{1}$$ $$ K_d =\dfrac{\ce{[A+][B-]}}{\ce{[AB]}}=\dfrac{(\alpha c_{0})(\alpha c_{0})}{(1-\alpha )c_{0}}=\...
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79 views

The source for the N-N bond dissociation energy of 240 kJ/mol in the table

Authoring an exam question, I made the mistake of taking a bond dissociation energy from a table I found on the internet. It comes in different styles, but is always labeled Table 7.1. It gives a bond ...
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69 views

Magnetic moment of trivalent lanthanide cations

The effective magnetic moment $\mu_{\mathrm{eff}}$ of tripositive rare earth elements, is calculated by $$\mu_{\mathrm{eff}}=g_J\sqrt{J(J+1)}\mu_\mathrm{B}$$ Why can't we use normal formula as $\sqrt{...
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71 views

What is the entalphy change with respect to pressure at Isothermal Process for *Real Gases*?

How much enthalpy of argon changes when the pressure is isothermally increased by $\pu{1 atm}$? (Gas should be considered as real gas under specified conditions) ($\pu{1 mol}$ of Argon gas is ...
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21 views

Why molar volume takes range of values along triple line whereas the temperature and pressure are constant along this line?

In the P-V-T surface the triple line is the line parallel to P-V plane on which three states of matter are in equilibrium. Temperature and pressure are same at all points along the triple line. But we ...
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1answer
158 views

Why are van der Waals' forces between gas molecules strong near its critical temperature?

My textbook says …easily liquefiable gases i.e. with higher critical temperatures are readily adsorbed as van der Waals' forces are stronger near the critical temperatures. What I do understand is ...
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24 views

API or database for verifying chemical reactions [closed]

Is there a database or API(rest calls) for verifying chemical equations? Example, Na + Cl -> NaCl + Loss of energy. So if I want to verify if there is a loss of energy or gain of energy? Is there ...
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31 views

Wave function of a perturbed system

In perturbation theory, wave function of a perturbed system can be expressed in a power series of some $\lambda$ as $\psi^{(0)} + \lambda\psi^{(1)}+\lambda^2\psi^{(2)}......$. Then we express ...
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249 views

Does solute concentration vary significantly with depth?

If I dissolve glucose in an ordinary beaker filled with water, are the concentrations of glucose at the top and bottom significantly different? What if we use NaCl as the solute? Is there a molecule ...
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1answer
25 views

Defintion of Solubility in Different cases

How do we define solubility (in moles per liter) in cases when concentration of cation is not equal to the concentration of anion? e.g. When we put AgCN in an acidic solution (Leading to formation of ...
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1answer
21 views

Dry paint becoming lubricant with heat

I am undertaking a physics experiment and have come up with a chemistry problem. Could paint perhaps become a lubricant under mild temperature. (It would take a while to explain my experiment, but an ...
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1answer
38 views

How can temperature be constant during a reaction? [closed]

So I was reading my textbook about the topic thermodynamics. Here the second paragraph States that the above equation describes the combustion of liquid ethanol at constant temperature and pressure. ...
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1answer
24 views

Deviation of azeotropic mixtures using raoults law [closed]

The book states the solution which shows large positive deviation from Raoult's Law form minimum boiling azeotrope What is meant by " minimum boiling azeotrope"
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35 views

Vapour pressure of a liquid subjected to pressure

I am following the derivation by Atkins in section 4B(c) (Physical transformations of pure substances; thermodynamic aspects of phase transitions), in which the authors derive the equation ${p = p_* * ...
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1answer
61 views

How can I model cellular membranes in terms of topology?

I'm reading from Principles of Physical Biochemistry by Kensal E van Holde (1998-01-06) in order to review some biochemistry and work my way toward a more mathematical approach to understanding ...
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21 views

Constructing a partition function for a gas-solid equilibrium in canonical ensemeble

For a closed system at fixed N,V,T there is a solid in equilibrium with its vapor. I'm told that I can minimize the helmholtz free energy to find that the equilibrium condition is given by $N_g = \...
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63 views

How to calculate the variation of enthalpy in a reaction that does not occur in standard conditions?

Standard enthalpy of formation is a value that represents the enthalpy variation in the formation of compounds with the purpose of using this values to know the enthalpy of a reaction where these ...
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44 views

Wave function of a harmonic oscillator

In a question it is given that consider $H-X$ chemical bond and find $H-X$ bond distance for which there is zero probability density of finding the proton. It is easy to solve we have just to ...
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1answer
61 views

Ground state term symbol for Cerium (Ce)

I need to calculate the term symbol of the ground state configuration of Cerium. The electron configuration is: $[Xe] 4f^1 5d^1 6s^2$ Since the d and f electrons are in different subshelles, they are ...
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1answer
110 views

Proposed mechanism for the catalyzed oxidation of CO by O3: Are NO and NO2 catalysts or intermediates?

The steps below represent a proposed mechanism for the catalyzed oxidation of $\ce{CO}$ by $\ce{O3}$: $$\begin{align} &\text{Step 1: } & \ce{NO2(g) + CO(g) &-> NO(g) + CO2(g)} \\ &...

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