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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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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148 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
56 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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32 views

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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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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100 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
96 views

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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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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1answer
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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
39 views

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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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
101 views

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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243 views

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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45 views

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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1answer
47 views

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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Calcium chloride hydrolysis

I was wondering about $ \ce{CaCl2} $ hydrolysis. The most primitive answer would have been: $ \ce{Ca(OH)2} $ does not dilute that great, therefore it is not strong enough to have the $ \ce{Ca^2+} $s ...
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1answer
61 views

Will group 2 chlorides dissolve in water in water or react to produce distinct products? How does this differ by the type of salt? [closed]

I thought it'd dissolve... but am i wrong? I added calcium chloride to water, and it was smoking, i was so confused. Can someone explain happened? I am doing an experiment where i dissolve salts in ...
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What is the effect of impurities on ice? [duplicate]

So, I know that the salt dissolves in the thin film of water on the surface of the ice, thus resulting in freezing point depression... but how exactly do i quantify this? Is there any effect on ...
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1answer
89 views

Why does activation energy depend on temperature? [duplicate]

To me it makes sense that the activation energy $E_\mathrm a$, as given by the Arrhenius equation, doesn't depend on the temperature as the needed energy (potential energy) to start a reaction has ...
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In what solvents does ionic association occur?

When a ionic compound like $\ce{NaCl}$ dissolves, it doesn't always full dissociate due to ionic pairing. This is measured by the van 't Hoff factor. Now, this is what I'm looking at for my chem ...
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How to reduce the surface tension of molten metals?

I'd like to reduce the surface tension of molten metals to reduce air bubbles by casting them like in this video with plaster. Actually the goal is to be able to cast gold without bubbles, but I guess ...
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67 views

Proof for second-order perturbation term of energy

In perturbation theory, if \begin{align}{\hat {H}} &= {\hat {H}^{(0)}} + λ{\hat {H}^{(1)}} \tag{1}\\ {ψ} &= {ψ^{(0)}} + λ{ψ^{(1)}} +λ^2{ψ^{(2)}} + ... \tag{2}\\ {E} &= {E^{(0)}} + λ{E^{...
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376 views

If you accumulate 100 identical spheres how many will end up on the surface?

So far I have asked this question in physics, engineering and math sections but have not gotten an answer in three years. If you have 100 identical spheres and group them into A sphere shape, how many ...
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3answers
97 views

Why does Vapor Pressure decrease on addition of solute? [duplicate]

Consider a vessel with a volatile liquid in it. Let's say it has a vapor pressure $P^0$ when it is pure. Now a non-volatile solute is added to it. Its vapor pressure decreases as $P^0\chi_{solvent}$. ...
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Polar protic solvents with melting point between between 0 °C and 25 °C [closed]

Need a solvent for a freezing point depression experiment. Acetic acid is the only one I know of, but it is not ideal due to the low freezing point depression constant. Any suggestions?
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When is Raoult's Law valid for solid-liquid solution?

Raoult's Law for solid-liquid solution is stated as such in my books that it is applicable for all non-volatile solutes. However different solutes must have different attractive or repulsive forces ...
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1answer
194 views

My Misconception of Entropy

It was recently brought to my attention that my understanding of entropy is wonky at best. In my experience, entropy was introduced (superficially at best) during general chemistry/foundations of ...
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Artificial Muscle | HASEL's Reaction

I was watching a TED-talk on artificial muscle, HASEL, where the inventor demos that an insulated oil in the presence of electric potential field gets displaced due to Maxwell stress inside oil. ...
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2answers
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Calculating the cell potential of a half cell from two half cell equations [duplicate]

I understand the premise of the question and how to solve it but I don't quite understand why I'm a factor of 2 out: Construct a potential diagram (at $\mathrm{pH} = 0$) for the reduction of aqueous $...
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1answer
48 views

How do i experimentally determine the vapour pressure of a solution? [closed]

So i wanna dissolve different salts in water and measure the vapour pressure of the resulting solution. I am doing this to compare the freezing point depression of different cations, used with the ...
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1answer
73 views

Why is change in internal energy not equal to zero during a phase transition? [closed]

Many books state that when there is no change in temperature $\Delta U$ is equal to zero. Why is this not applicable for phase transitions? I have had this question for a while now and have been ...
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181 views

Balancing a reaction where dichromate ion reacts with ethanol to give Cr(III) and carbon dioxide

I have only started to learn balancing redox reactions, and a recent question has me confused. The question is : Balance in both acidic medium and basic medium: $$\ce{Cr2O7^2- + C2H5OH -> Cr^3+ + ...
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Why is vapor pressure constant at boiling point?

At non-boiling point, I understand that when you add heat, temperature increases and also the amount of gas increases, so by using $PV=nRT$ at constant volume, the increase in $n$ and $T$ would ...
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How to use Clausius-Mossotti equation to determine the molecular structure of a compound? [closed]

A question in my exam came as follows: Explain the Clausius-Mossotti equation. How is it used in establishing the molecular structure of a compound? I have studied the Clausius-Mossotti equation and ...
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1answer
61 views

Finding concentration of hydronium ions in water after adding hydrogen chloride gas [closed]

A sample of hydrogen chloride gas, $\ce{HCl}$, occupies $\pu{0.932 l}$ at a pressure $\pu{1.44 bar}$ and at a temperature of $\pu{50^\circ C}$. The sample is dissolved in $\pu{1 l}$ of water. What is ...
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1answer
143 views

Kinetics question regarding Rate Law

The acid catalysed hydrolysis of an compound $\ce{A}$ at $\pu{303K}$: $$\ce {A ->[$k$] B}$$ has a half-life of $\pu{100 min}$ when carried out in a buffer solution of $\mathrm{pH=5}$ and $\pu{10 ...
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1answer
80 views

What explains the case hardening color effect?

Year 11 chemistry student here. I'm curious about how the case hardening effect works on metals. I know that when the electrons gain an energy 'level' or lose an energy 'level' they emit light at ...
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297 views

Calculating numbers of moles at equilibrium given the volume of mixture and initial concentration of reactants [closed]

The equilibrium between three substances, A, B and C Is shown below. $$\ce{A(g) + B(g) <=> C(g)}$$ Initially there were $\pu{0.1 mol}$ of A and $\pu{0.2 mol}$ of B in the reaction mixture. A and ...
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646 views

Why is the first ionization enthalpy of molecular O2 less than atomic O?

A cousin of mine asked for my help to answer one of his homework questions. It stated- Explain why- The first ionization energy of molecular oxygen $\ce{O2}$ ($\pu{1175 kJ mol-1}$), is lesser than ...
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1answer
58 views

How to experimentally determine the chemical potential of salt water? [closed]

I have NaCl dissolved in water. How do I find the chem potential?
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Is is valid to compare reaction quotient to $K_p$ as well as $K_c$?

Can I use the reaction quotient compared to $K_p$ to answer the following question? The solid $\ce{XY}$ decomposes into gaseous $\ce{X}$ and $\ce{Y}$: $\ce{XY(s) <=> X(g) + Y(g)}$ with a $K_p = ...
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Calculate inert molar flow rates in absorption column

In an absorption column the absorption of $\ce{CO2}$ from air to water is being studied. The in-flow of water is $\pu{5 dm3/min}$, the in-flow of air is $\pu{4.5 dm3/min}$ and the $\ce{CO2}$ flow is $\...
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116 views

Deriving an expression for reaction time in terms of the total concentration

Consider the dimerization of protein $\ce{A}:$ $$\ce{2A <=> A2}$$ with forward rate constant $k_1$ and backwards rate constant $k_{-1}.$ Derive the following expression for the reaction time in ...
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Can single molecules of C and O2 react in isolation, and if so how will momentum be conserved?

I am trying to figure out how is it possible to reconcile the reality of exothermic reactions, which means that kinetic energy is transferred to (heats) the surrounding matter, with the principle of ...

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