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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Molar volume of salt

A 4% (weight percent) solution of a salt with Mr = 189.6 g mol-1 was prepared at 25 0C. The density of the prepared solution was 1.00926 g cm-3. The density of water at 25 0C is 0.99707 g cm-3, and ...
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How to find out equivalent to about 2 mg of sodium in sodium metabisulphite? [closed]

How to find out equivalent to 2mg of sodium in sodium metabisulphite? Please help to find out this problem.
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Entropy of a van der Waals' gas

I would like to ask how I could derive the entropy change $dS$ for a van der Waals' gas. I think I would need to use the total differential of entropy and then use the Maxwell relation shown below. ...
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How can I solve for the volume that is required to solve for the work due to vaporization?

Problem A sample of ice weighing $\pu{18.02 g},$ initially at $\pu{-30.0 °C},$ is heated to $\pu{140.0 °C}$ at a constant pressure of $\pu{1.00 atm}.$ Calculate $q,$ $w,$ $ΔE,$ $ΔH,$ and $ΔS$ for ...
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Meaning of 'constant T and p'

In chemical thermodynamics, the condition "constant temperature and pressure" appears almost everywhere. However, I felt a small ambiguity in the phrase so I wanted to clear my doubts. When ...
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1answer
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About covalant bound for molecule : repulsion of electrons?

I try to understand, from the electromagnetic side only, how the molecule could be more stable than each atom, and concluded that it could not. Where is my mistake ? Here is an illustration : By using ...
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Calculating commutator of parity operator and e^(d/dx) [closed]

How do we evaluate the commutator of the above? If they commute, we could prove that the linear translation operator and the parity operator also commute. Intuitively it makes sense because, P(x-a)=-x-...
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How does solutions of two liquids work?

I'll start by establishing my potentially flawed understanding of solutions: A solution is a completely homogenous mixture. That means that the two (or more) substances are evenly distributed ...
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Still confused about thermodynamic processes

I'm trying to visualize a simultaneously adiabatic and isothermal process like large amounts of an ideal gas in a vacuum. As I understand, $ \delta Q = 0$ in adiabatic processes, and $T$ is constant ...
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Choosing the correct formula for Helmholtz energy

Calculate Helmholtz energy $(ΔA)$ from the following processes. Consider that both processes are reversible and isothermal. a) The melting of $\pu{36.0 g}$ of ice, $\ce{H2O(s)},$ in liquid water $\ce{...
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N factor in redox reactions [closed]

What does n factor actually represent in redox reactions (Excluding acids and bases) Is it the gain in electrons or just the change in oxidation state
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Why is melting point of Vanadium higher than Iron?

The iron is found to have four unpaired electrons while vanadium has 3 of them. we say the binding energy is directly proportional to number of unpaired electrons and hence number of metallic bonds ...
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enthalpy for physical chemistry [closed]

The standard enthalpy change of vaporization of water is +40.7 kJ mol-1. An electric kettle is rated at 3kW (1kW = 1 kJ s-1). How long will it take to evaporate 1.0 kg of water at 100°C? Give the ...
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Regarding salt hydrolysis of weak acid - weak base salt

For a salt made from a weak acid and weak base, say $\ce{NH4CN}$, my textbook represented hydrolysis at equilibrium by this reaction: $$\ce{NH4+ + CN- +H2O<=>NH3 + HCN}\\\text{ }\text{ }\text{...
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What does A and B represent in the given figure of p orbital [duplicate]

1 spherical node, radial node 2 angular node ,radial node 3 radial node, angular node 4 angular node, planar node Choose any 1
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Beer-Lambert law absorption by each species

Light travels length $l$ through a medium with $n$ independently absorbing species with extinction coefficients $\alpha_1,\dots,\alpha_n$. According to Beer-Lambert law, the amount of light absorbed ...
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liquid crystal and light

The liquid crystal can be control using polarizes light. This means we can control the arrangement of the liquid crystal molecules, then when the light passes through it can be manipulated. But why ...
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What makes concentrated aqueous solutions of aluminium nitrate and aluminium chloride suitable to dissolve noble metals, specifically gold? [closed]

Aluminium nitrate is a strong oxidising agent and aluminium chloride acts as a Lewis acid. Also these solutions are claimed to have the abilities of aqua regia and therefore can dissolve noble metals. ...
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Why is chemistry unpredictable?

Disclaimer: I am not a chemist by any means, and I only have knowledge limited to what I learned in my university's Chemistry III course. Basic understanding of everything up to valence electron ...
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Does the acid dissociation constant takes hydrogen ions from water into account?

For the dissociation of a weak acid: $$\ce{HA(aq)<=>H+ + A-}$$ To calculate $\mathrm{pH}$ of a weak acid, we use the expression: $$K_\mathrm{a}=\ce{\frac{[H+] [A-]}{HA}}$$ The $\ce{[H+]}$ has ...
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Sign of work done by gas during isothermal expansion

$\pu{10 mol}$ of an ideal gas confined to a volume of $\pu{10 L}$ is released into atmosphere at $\pu{300 K}$ where the pressure is $\pu{1 bar}.$ The work done by the gas is: Work done can be found ...
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Question about reading NIST datasheets & Gibbs energy of reaction

I'm peeping the NIST thermo tables for $\text{H}$ and $\text{H}_2$, and I'm perplexed. Seems to me that using $$G=[\Delta H^\circ_f+H-H^\circ(T_r)]-T\cdot S^\circ$$ (well, actually correcting the ...
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Is there an 'easy' way to determine if a ligand is a pi acceptor, donor or neutral?

First of all I am confused how something can be pi neutral? something either does or doesn't have filled p orbitals for example. given something I have never seen acting as a ligand before like ...
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2answers
70 views

Will equilibrium ever establish if one of the products starts to disassociate?

When $\ce{N_2O_5}$ is heated at a certain temperature, it disassociates as $$\ce{N_2O_5 (g)<=>N_2O_3 (g) + O_2 (g); K_c = 2.5}$$ At the same time $\ce{N_2O_3}$ also decomposes as $$\ce{N_2O_3 (g)...
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Units to use in Morse potential Equation

I am to graph the Energy potential curve (in $\text{cm}^{-1}$) for a molecule (HI),in the fundamental electronic state, according to the Morse oscillator. I believe I am to use this equation $$E(R)=...
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Symmetry Operation on Product of Functions

In regards to direct product representations, I'm trying to find a proof for: $R(X_iY_j)=R(X_i)R(Y_j)$ Where $R$ is a symmetry operation of a group and $X_i$ and $Y_j$ are members of different basis ...
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Beer Lambert law when complex is tetragonal (Jahn-Teller elongated)

I wondered what modifications there would be to the Beer Lambert law to find the molar extinction coefficients for the solution if the solvent contained the ligands which bind to the metal centre of a ...
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1answer
79 views

Why isn't standard Gibbs energy zero at equilibrium?

At equilibrium, everything that $G$ depends on is constant. The Gibbs' free energy may have been given to you without really emphasizing that it is actually a function of temperature, pressure, and ...
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Internal pressure, but from other variables

The internal pressure is derived by differentiating internal energy with respect to the natural variable in one term while holding the unnatural variable in the other term constant. $$\mathrm dE = T\,\...
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Equilibrium constant and stoichiometry [duplicate]

In the expression of equilibrium constant, each concentration term is raised to the power of their stoichiometric coefficient. But this could affect the equilibrium constant. For example, we can write ...
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1answer
47 views

Finding the equivalent weights of the oxide and the metal when reduced by hydrogen [closed]

A metal oxide ($\pu{1.80 g}$) required $\pu{833 ml}$ of hydrogen at NTP to be reduced to its metal. What are the equivalent weights of the oxide and the metal? My attempt: $$\text{equivalent of metal ...
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Combustion of cyanamide in a bomb calorimeter at constant volume and at 25°C

In a bomb calorimeter, cyanamide was subjected to combustion at constant volume, and the heat evolved was found to be $\pu{742.7 KJ}$ at $\pu{25 ^\circ C}$. Find $q_p$. This is a question in my ...
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2answers
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Can reversible reactions proceed by different mechanisms in the forward and reverse directions? [closed]

It seems odd to me that this would be the case, but it also seems odd that it wouldn't. Imagine a mechanism for a (forward) reaction that includes a slow reversible step and a fast irreversible step: ...
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What is the change in enthalpy for an adiabatic expansion?

I am just wondering if ∆H can be equal to 2∆U for an adiabatic expansion as q=0 in adiabatic process so ∆U would be equal to work done for changing volume and ∆H=∆U+work done in expansion.
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Why does conductance become constant during precipitation?

I recently came across this question where $\ce{AgNO3}$ was slowly added to a solution of $\ce{KCl}$ and we have to figure out the graph of conductance vs volume of $\ce{AgNO3}$ added. In the answer, ...
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1answer
67 views

Difference between Helmholtz free energy and normal free energy

I know that free energy is defined as the amount of work that a system can do at constant temperature and and its formula is F=U-TS and that by definition Helmholtz free energy is the amount of work a ...
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1answer
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What is the significance of enthalpy?

I an getting confused between enthalpy and internal energy. My textbook says that change in enthalpy is the sum of change in internal energy and the amount of work done in expansion or compression but ...
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Does #4 LDPE Plastic Bottle Leach into Water?

I understand that Water Bottles expire due only to the fact that the plastic can degrade over time and leach into the water making the water's taste not as desirable as the manufacturer might intend. ...
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2answers
59 views

Applicability of Enthalpy-Heat relation for a non-isobaric process

Consider a process in which state variables changes from $(p_1, V_1, T_1)$ to $(p_2, V_2, T_3)$ . I've learned that to calculate the change in enthalpy for any process, we consider a hypothetical ...
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In Energy-Dispersive X-ray Spectroscopy, do higher atomic elements ever generate just K lines without L or M lines?

The heavier elements only show L or M lines. Is that because the critical ionisation energy is too high to get K lines in higher atomic numbers? Can you ever get just the K lines, or just the M lines ...
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1answer
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interconverting Van Der Waal's equation for real gases from number of molecules to density

I want to ask a question about Van Der Waal's equation for real gases. I was shown the following formula for real gases (VDW) which accounts for the liquification of water vapour which is not possible ...
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Ratio of rates of diffusion of gases

I stumbled upon a question, A mixture of 50 mL of Hydrogen gas and 50mL of Oxygen gas is allowed to effuse through an effusimeter. After some time it is observed that the residual gas occupies 90mL. ...
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1answer
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Doubt about Van Der Waals equation

I got how the real pressure would be less than ideal pressure due to net force of attraction between gas molecules acting towards the center. But, why is the real volume greater than ideal volume? I ...
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1answer
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About spontaneous combustion of methane

I heard that spontaneous reaction happens if $\Delta G=\Delta H-T\Delta S$ is negative. For combustion of methane, according to Chemguide: $\Delta H=\pu{-891.1 kJ K^{-1} mol^{-1}}$ $\Delta S=\pu{-0....
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Vapour density dependence on temperature

Does vapour density change with temperature or is it solely dependent on molecular mass as per the formula VD=molar mass/2
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How would I correct this Hess cycle?

Given $$\ce{2 SO2(g) + O2(g) <=> 2 SO3(g)} \quad \Delta_\mathrm{r}H = \pu{-196.0 kJ mol^-1}$$ and $\Delta_\mathrm{f}H(\ce{SO2}) = \pu{-296.0 kJ mol^-1},$ find $\Delta_\mathrm{f}H(\ce{SO3}).$ I ...
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13C-NMR of aniline: Why are carbons that are further from the amine group more downfield than carbons that are closer? [closed]

A $\ce{^{13}C}$-NMR of aniline shows that the carbons further from the $\ce{-NH2}$ group are more downfield than the ones near the top of the benzene ring. If electronegative atoms like nitrogen have ...

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