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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46 views

Order of reaction for hydrogen ions being ignored

I have been reading through a case study about calculating the order of reaction for the following reaction: $$\ce{H2O2 + 3 I- + 2 H+ -> I3- + 2 H2O}$$ The paper uses an iodine clock reaction ...
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1answer
300 views

Reaction with tin(IV) iodide and hydrogen peroxide [closed]

Today I reacted tin(IV) iodide $\ce{SnI4}$ (dissolved in water) with hydrogen peroxide. This produced a yellow/brown colour (I'm guessing due to formation of $\ce{I2}?).$ I then added some petroleum ...
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1answer
26 views

What exactly causes equilibrium to shift when pressure is decreased? [duplicate]

Take the reaction: $$\ce{N2(g) + 3 H2(g) <=> 2 NH3(g)}$$ If pressure is decreased, equilibrium shifts to the left because it has more moles. I understand the basics of why this is, i.e. due to ...
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2answers
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Why when deriving the Clapeyron equation can you assume that dH = dq, as surely the pressure is not constant?

Part of the Clapeyron equation involves replacing $\Delta S$ with $\Delta H/T$. I can see the step from $\Delta S$ to $\Delta q/T$ but I'm not sure why you can replace $\Delta q$ with $\Delta H$. From ...
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1answer
75 views

What is the electrochemical reaction of this battery?

I've watched a YouTube video "Soda Can Battery - Power From Trash - DIY Project" by Source Port Services. I understand that the anode can be oxidised, but what is the reduction reaction at the cathode?...
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44 views

Feasibility of using ionic liquid fuels in an MHD type reactor

First off I would like to say that my knowledge on chemistry, even general chemistry, is basic if not poor. That said, I have some intuituions on this matter. I haven´t found any paper regarding ...
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1answer
42 views

Under what circumstances that Liquid-Liquid extraction would be good to use? [closed]

Under what circumstances that LLE would be useful ? Are the 2 top reasons - 1. Difference between the boiling points of the components are very low or similar. 2. For Temperature sensitive compounds ...
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1answer
57 views

Finding change in activation energy from change in rate constant in catalysis

I need to find by how much the activation energy decreases when the rate constant increases by a '$x$' factor when a catalyst is used in the reaction. I'm just super confused about how to solve this....
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179 views

Ground state term symbol, why is $L = |M_L|$, if L must be a maximum?

I'm trying to understand how to predict ground state term symbol of atoms. After finding the biggest S, why the biggest L will be $L = |M_L|$, where $M_L = \sum m_l$? I know this rule works to ...
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46 views

Energy of mercury(II) oxide decomposition

Study check 9.11 from [1, p. 298]: Mercury(II) oxide decomposes to mercury and oxygen. $$\ce{2 HgO -> 2Hg + O2}\quad ΔH = \pu{+182 kJ}$$ […] b. How many kilojoules are needed when ...
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1answer
48 views

Energy required for obtaining required mass of aluminium from alumina via electrolysis

How do I know how much energy I need to obtain 20 g alumunium from alumina with 5 V? I calculated the quantity of electricity is 2.22 F. Any help appreciated!
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40 views

Internal energy change for reactions at constant volume vs constant pressure

The reaction of cyanamide, $\ce{NH2CN(s)},$ with dioxygen was carried out in a bomb calorimeter, and $∆U$ was found to be $\pu{–742.7 kJ mol-1}$ at $\pu{298 K}.$ Calculate enthalpy change for the ...
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Could I make a lava lamp using diluted oil paint for the blobby part?

So, on a whim I decided to try making a lava lamp for my roommate. I know that lava lamps are made with dyed water/salt water and a trade secret mix of paraffin/wax/dye/heavy solvent that is just ...
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3answers
183 views

melting and boiling …really equilibrium? [closed]

Why are melting and boiling considered equilibrium processes even though the amount (concentration) of both phases keep changing i.e from solid to liquid and so on?
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47 views

Is it possible to create an arbitrary, stable, unique chemical fingerprint? [closed]

Context: I want to be able to hash real-world objects Is it possible to create a substance containing a combination of elements (or isotopes?) in a random and difficult to reproduce (but simple to ...
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1answer
96 views

Decomposition of total Interaction energy with SAPT or EDA-NOCV

I want to perform energy decomposition analysis for some Hydrogen bonded complexes. I came to know that ORCA and Psi4 allows EDA-NOCV an SAPT(0,2,3) respectively. But I do not know which one would be ...
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43 views

During solid-solid phase transition, if both solid phases are incompressible, is ΔG independent of p?

Source: Atkins Physical Chemistry, Ninth Edition, page 154, Problem 4.13: Show that, for a transition between two incompressible solid phases, ΔG is independent of the pressure. My attempt: ...
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27 views

Carbon Capture Absorption with Henry's Law

Assume the Henry’s coefficient for water at $\pu{20 °C}$ is $\pu{1.6E8 Pa}.$ What is the mole fraction of $\ce{CO2}$ that will be dissolved in water assuming that it is at equilibrium with a flue gas ...
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1answer
49 views

Intuition for the overlap integral

I want to ask a question about the overlap integral. I was studying about the MO diagram of $\ce{H_2^+}$ and we managed to derive an expression which had the following term: $$\langle \mathrm{1s}_\...
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3answers
118 views

Effect of dilution on the degree of dissociation of an electrolyte

My book says that on dilution, the degree of dissociation of an electrolyte increases. Consider the reaction: $$\ce{A(aq) <=> C(aq) + D(aq)}$$ Let $\ce{A}$ be the electrolyte that splits into ...
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2answers
30 views

Moving water vapour between flasks [closed]

I have a flask of silica gel connected to a flask that contains a bit of water, so when I heat the silica gel the water absorbed gets evaporated and I want it to move to the other flask, but it always ...
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75 views

Gibbs free energy of phosphorus pentachloride decomposition reaction

The equilibrium constant at $\pu{227 °C}$ for the equation $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$ is $K_p = \pu{4.50E3 bar}.$ Calculate the value of $Δ_\mathrm{rxn}G^\circ$ at $\pu{227 ...
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2answers
78 views

Real Gas Behaviour

For a fixed amount of a real gas when a graph of $Z$ vs $P$ was plotted, then at a very high pressure slope was observed to be $\pu{0.01 atm^-1}.$ At the same temperature and pressure if a graph is ...
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176 views

Heat involved in isenthalpic process

Question 28 from [1, p. 4.4]: An ideal gas is expanded irreversibly from $\pu{5 L}$ to $\pu{10 L}$ against a constant external pressure of $\pu{1 bar}.$ The value of heat involved $(q)$ in this ...
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115 views

Clarification on the Clausius inequality

In Atkins' Physical Chemistry the criteria for spontaneity using Gibbs energy was calculated using the Clausius inequality: $$\mathrm dS ≥ \frac{\mathrm dq}{T},$$ and at constant pressure, $\mathrm ...
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1answer
56 views

Thermodynamic statements [closed]

Question 13 from [1, p. 4.2]: Which of the following statements is true? (a) An ideal gas always obeys the equation: $PV^γ = \mathrm{constant}$ in adiabatic process. (b) An ideal gas ...
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2answers
237 views

Calculating partial pressure of carbon monoxide

$\ce{ZnO}$ is exposed to pure $\ce{CO}$ at $\pu{1300 K}$ and the equilibrium $$\ce{ZnO(s) + CO(g) <=> Zn(g) + CO2(g)}$$ is then established at $\pu{1 atm}$ pressure. The density of the ...
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1answer
62 views

What is the interaction between dissolved ions of opposite valence in a solution at rest?

NaCl is dissolved in water. Ions sodium and chloride are sufficiently free from each other so that they may occupy different regions of the solution after an active transport process through a ...
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35 views

What is the effect of applied magnetic field on absorption spectrum?

Upon application of a weak magnetic field, a line in the microwave absorption spectrum of rigid rotor splits into $3$ lines. The quantum number $(J)$ of the rotational energy level from which the ...
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3answers
86 views

Is enthalpy of combustion the 'heat released' or 'enthalpy change'?

In a constant volume calorimeter, $\pu{3.5 g}$ of a gas with molar weight $\pu{28 g}$ was burnt in excess $\ce{O2}$ at $\pu{298 K}.$ Temperature of calorimeter increased from $298$ to $\pu{298.45 K}$ ...
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33 views

Can I use the quasi-equilibrium approximation when drug and ligand distribution volumes are different?

A drug $D$ binds a ligand $L$ to form a complex $C$ according to the law of mass action. Furthermore, mass balance should be achieved. Can I still assume quasi-equilibrium when the distribution ...
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2answers
92 views

How is energy not stored in bonds? [duplicate]

Consider the paraphrase from Ebbing: It takes energy to break bonds & energy is released when bonds are formed Let's look at the first statement It takes energy to break bonds. Is this true ...
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1answer
88 views

Is it really possible for a liquid to stay afloat a gas (vapor)?

I have a book at home called Chemical Thermodynamics for Process Simulation (I have the first edition) and at the very beginning of chapter 2 of the book one may read the following: No reference is ...
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2answers
421 views

Phenolphthalein Indicator mixed with base that first turns pink and then clear

What occurs in the following situation: After adding 2 drops of Phenolphthalein Indicator (an indicator that turns bases pink and stays clear for acids,) into a unknown solution, the solution turns ...
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1answer
56 views

Why does an electron lose energy so that it falls back to a lower energy state than just stay at the higher energy state?

Suppose an electron in the 2nd shell gets excited and jumps to the 4th shell. Shouldn't the electron then exist in an unstable equilibrium in the 4th shell, than lose energy and drop down to the 2nd ...
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1answer
64 views

Heat exchange in adiabatic process

I know my teacher told me that In adiabatic process there is no exchange for heat between system and surrounding. Then he came to point. From first law of thermodynamics $$∆U = q + W \tag{1}$$ ...
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49 views

Electric fields in a galvanic cell

I have read hat there is two types of electric fields exist in galvanic cell.I understand E because of charges accumulated on electrodes but what about other E -field? What does cause this field and ...
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44 views

How to achieve Löwdin transformation?

I use Gaussian 09 to obtain the Hamiltonian and overlap matrices, $H_0$ and $S_0,$ where the B3LYP functional and the 6-31G basis set are adopted. Then how to transform the system to an orthogonal ...
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49 views

Why is $E°_{cell}$ not $\Delta E°_{cell}$?

$E°_{cell}$ is the EMF of the cell for a reaction with respect to standard hydrogen electrode(SHE). So why don't we represent $E°_{cell}$ or $E_{cell}$ by $\Delta$ symbol, in the same manner in which ...
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1answer
80 views

How strong are molecular bonds in layman's terms?

Suppose you had a single sheet of graphite the size of an A4 page. What would it feel like to handle it? Would your fingers instantly tear through it as you tried to grasp it? Could you punch your ...
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187 views

What is the purpose of phase matching when drawing a MO diagram?

During the lecture, we were learning how to draw the MO diagram for $\mathrm{BF_3}$. I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My ...
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1answer
38 views

Explain me concept of vapour pressure like I am five [closed]

I have browsed internet to understand the concept of vapour pressure but something isn't linking for me. How do we relate vapour pressure to temperature for liquid only and any simplified definition ...
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2answers
629 views

d-Menthol vs dl-menthol: Does an enantiomer and its racemic mixture have different melting points?

I am checking out Wikipedia and it shows a different melting point (m.p.) for l-menthol $(\pu{42 ^\circ C}$ to $\pu{45 ^\circ C})$ vs dl-menthol $(\pu{36 ^\circ C}$ to $\pu{38 ^\circ C}).$ How is ...
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57 views

Chemical Kinetics regarding Iodination of Cyclohexanone

We did an experiment to determine the overall order of iodination of cyclohexanone. Rate of a certain chemical reaction = $\ce{k[A]^p[B]^q[C]^r}$ so the overall order = p+q+r We're referring to a ...
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2answers
173 views

Why does the dipole moment of molecules go from positive to negative? [duplicate]

In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition). This makes sense ...
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1answer
112 views

Ratio of uncharged to charged side chains [closed]

The $\mathrm{p}K_\mathrm{a}$ of the side chain imidazole group of histidine is $6.0.$ What is the ratio of uncharged to charged side chains at $\mathrm{pH}~7?$ Here's my attempt to the solution: $$7 ...
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1answer
405 views

Chemical kinetics

Consider a reversible reaction $\ce{A}$ converts to $\ce{B}$ and $\ce{B}$ converts to $\ce{A}$ with forward and backward rate constants $k_\mathrm{fwd} = k_\mathrm{rev }= \pu{1 s-1}.$ Suppose we start ...
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2answers
124 views

Is “density per unit volume” something?

I was reading articles on the preparation of shellac-based composites when I encountered the following statement (in ref. 1): Wood flour and fibres are interesting because of their low cost, good ...
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53 views

Is there any publicly available software that can do deterministic CCSDTQP other than MRCC?

MRCC can do arbitrary order coupled cluster but much of the code is computer-generated (not hand-coded by a human) so it can be slow. There are some stochastic codes for high-order coupled cluster, ...
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1answer
51 views

Can someone walk me through this gas mixture question?

Argon $(\ce{Ar})$ and helium $(\ce{He})$ are initially in separate compartments of a container at $\pu{25 °C}.$ The $\ce{Ar}$ in compartment A which has a volume $V_\ce{A}$ of $\pu{9.00 L}$ and a ...