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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7
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1answer
2k views

How exactly is activation energy defined?

In a common interpretation of the Arrhenius rate equation $$k = A\exp\left(-\frac{E_\mathrm a}{RT}\right),$$ the activation energy $E_\mathrm a$ is understood to represent the difference in the ...
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Stoichiometric defects in silver bromide

Stoichiometric defects (Schottky and Frenkel defects) in ionic crystals are formed due to irregularities in the ionic arrangement which maintain the stoichiometry and electroneutrality of the solid. ...
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How to detect H₂SO₄ (aq) and NH₃

We have two bottle named $\ce{H2SO4~(aq)}$ and solution of $\ce{NH3}$ but we don't know their name actually. What I have to do to detect these solution by only using : $\ce{CuCl2}$ or $\...
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Is it possible to save an insoluble snowflake?

In The Big Bang Theory Season 3 Episode 1 "The Electric Can Opener Fluctuation" Leonard gives Penny a snowflake that will never melt. He said some type of chemical gas name when he try to explain, ...
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530 views

Why was anhydrous magnesium carbonate “upsalite” discovered so late?

What complicated the synthesis of upsalite (anhydrous $\ce{MgCO3}$), for it to be synthesized and published in 2013 as opposed to the 20th century, as one would expect for such a simple salt?
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How to calculate the probability of finding an electron in a box between 0.25L and 0.75L?

If the wavefunction of the electron in a box of length $L$ is $$\psi{(x)}=\sqrt{\frac{2}{L}}\cdot\sin{\frac{n\pi x}{L}}$$ What would be the probability of finding the electron between $0.25L$ and $0....
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1answer
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Clarifications on thermodynamic cell efficiency

The thermodynamic efficiency of any cell (especially Fuel cells) is given as $$\frac{\Delta G}{\Delta H} \times 100$$ I understood this partly, that since $\Delta G$ is the useful work obtained in ...
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2answers
880 views

Is sublimation caused by an environmental difference or an element's composition?

I was having a conversation when the topic of sublimation came up. Prior to the discussion, I had always thought that sublimation was caused by a great pressure/temperature difference, but another ...
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Nuclear fusion reactions violate law of conservation of mass, but it has not yet been taken into account. Why?

According to the law of conservation of mass, during any physical or chemical changes, the total mass of the products is equal to the total mass of the reactants. But in nuclear fusion reaction if ...
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2answers
667 views

The ionization energy of H₂⁺ molecule ion

I am trying to compute the ionization energy of $\ce{H2+}$ molecule ion from the electronic energy spectrum. The question is whether one should use the purely electronic Hamiltonian or the Hamiltonian ...
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Why are sigma bonds stronger than pi bonds?

Why are sigma bonds stronger than pi bonds?
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993 views

What is advantage of creating elements that disappear in a flash?

More than dozen of heavy elements of periodic table do not occur naturally but are prepared artificially at nuclear reactors.. These elements are said to disappear in a flash.. So, why invest lot of ...
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1answer
5k views

Find the number of copper spheres in a box

A box contains a mixture of small copper spheres and small lead spheres. The total volume of both metals is measured by the displacement of water to be $\pu{420 cm^3}$ and the total mass is $\pu{5.4 ...
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1answer
11k views

Calculating standard enthalpy of reaction, which reactant to choose for the amount of substance

For example, this reaction: $$\ce{2NaOH + H2SO4 -> Na2SO4 + H2O}$$ Suppose both concentrations are $1\ \mathrm{mol\ l^{-1}}$ (standard condition). There is $0.02\ \mathrm{mol}$ ($20\ \mathrm{cm^3}$...
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Transition state and free energy

We have products $\ce{A + B}$ combining to form $\ce{C + D}$ through the transition state $\ce{X}$. Are all reactions at least virtually reversible? Is the difference between a reversible reaction ...
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303 views

Prediction of ionic reduction?

Here are some standard electrode potentials:- $$\ce{SO_4^{2-} + 4H^+ + 2e^- -> SO_2 + 2H_2O}\\E^o=0.17\mathrm{V}\\ \ce{NO_3^- + 4H^+ + 3e^- -> NO + 2H_2O}\\E^o=0.97\mathrm{V}\\ \ce{NO_3^- + ...
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1answer
336 views

Superheating metal alloy above solidus

Is it possible to heat a material above its solidus without melting occurring? More specifically, at a heating rate of approximately 200K/s, will a metal alloy exhibit superheating and if so by what ...
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1answer
140 views

Is the current situation possible for recreaction in a lab?

I want to convert cellulose to another form (crystalline => amorphous). Cellulose requires a temperature of 320 °C and pressure of 25 MPa to become amorphous in water.(Is the pressure achievable in ...
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2answers
975 views

Why is water evaporation not more commonly used to cool buildings [closed]

Water has a very high heat of vaporization (2260 kJ per kg). Why not just gradually sprinkle water on your roof to keep the building cool in opposed to using air conditioners? It wouldn't take much ...
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3answers
10k views

Express the maximum work from a voltaic cell

The net cell reaction of an electrochemical cell and its standard potential is given below: $$\ce{ Mg + 2Ag+ ->Mg^{2+} + 2Ag} \ \ \ \ \ \ \ \ E^\circ=3.17\:\mathrm{V}$$ The question is to find the ...
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1answer
2k views

Which elements have no liquid form at atmospheric pressure?

Carbon has no liquid form at atmospheric pressure. Is this unique amongst naturally occurring elements? The more interesting and vague question is, is this property somehow important or related to ...
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What is known about liquid carbon?

The wiki tells me that if you heat carbon at atmospheric pressure it eventually turns directly into a gas without being liquid first. At what pressure can you make liquid carbon? Has anyone actually ...
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If the pH is zero, what would be the normality of a sulphuric acid solution?

If pH of the solution is zero, what would be the normality of $250 \, \mathrm{ml}$ $\ce{H2SO4}$ solution? My work: $\mathrm{pH} = 0$, hence the concentration of $\ce{H+}$ ions is $\pu{1 mol L^-1}$, ...
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Why search new elements?

I've read this today. From the little I know, they discover new elements by bombarding some atoms in particle accelerators (I guess) and these new elements last a few miliseconds. So what's the ...
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Is there any relationship between ultrasonication and temperature

In chemistry we use ultrasonication for cleaning vessels ,synthesis of chemical compounds (sonochemistry) etc.I know that during ultrasonication high temperature and pressure is formed "locally".But I ...
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1answer
397 views

Thermodynamics behind Deliquescence?

The phenomenon of deliquescence wherein a water soluble substance absorbs water from atmosphere and dissolve in it forming a saturated solution, has thermodynamic roots. I have read the fact that the ...
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Entropy and enthalpy change on mixing liquids

Question: A concentrated solution of copper sulphate, which is dark blue in colour, is mixed at room temperature with a dilute solution of copper sulphate, which is light blue. For this process: ...
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1answer
406 views

Identifying the gas given ratio of its specific heats

The ratio of the heat capacities $\frac{C_\mathrm p}{C_\mathrm v}$ for one mole of a gas is $1.67$. The gas is: a) $\ce{He}$ b) $\ce{H2}$ c) $\ce{CO2}$ d) $\ce{CH4}$ I know how to answer ...
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1answer
270 views

Storing kinetic energy in bonds

Let's assume a setup with a static linear molecule with three identical atoms connected by bonds and a single atom, identical to the other three, being shot at the molecule. Let's also assume that ...
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1answer
6k views

Finding electron configuration of lanthanide ions

When I have a gadolinium ion ($\ce{Gd^3+}$), how can I calculate its electron configuration? $$\ce{Gd} : \mathrm{[Xe] (4f)^7 (5d)^1 (6s)^2}$$ Do I need to first subtract the 2 electrons in the $\...
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2answers
26k views

Difference between Reaction Rate and Rate Law?

Lets say you have the reaction $$\ce{$a$A + $b$B -> $c$C + $d$D}$$ The rate of the reaction is given by the change in initial concentration over the change in time. $$-\frac{\Delta \left[\ce A \...
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100 views

Balancing Oxidation-Reduction equations

Anode: $\ce{2 H2O_{(l)} -> O2 + 4 H+_{(aq)} + 4e^-}$ Cathode: $\ce{ 2 H2O_{(l)} + 2 e- -> H2_{(g)} + 2 OH-_{(aq)}}$ Can someone show me the steps for adding the two. For the overall reaction,...
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0answers
390 views

How will the transference number of H+ ion in a dilute solution vary as temperature increases?

I know that transference number depends on Ionic mobility, which depends on temperature. But is there any equation which describes the relation of Transference number and temperature, any ions like H+....
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1answer
4k views

What is the colloidal osmotic pressure?

The oncotic pressure or colloidal osmotic pressure is the osmotic pressure developed due to the presence of colloids in a solution. But since the colloids are not true solution, why should the ...
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3answers
8k views

Activity of hydrogen ion

I am not from chemistry background. Could you tell me in simple words what the activity of hydrogen $a_{\ce{H+}}$ is? It arises in the context that the negative logarithm of the activity of hydrogen ...
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4answers
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Unit of the equilibrium constant: contradiction of Bridgman's theorem?

The following equation is standard in thermodynamics: $$ \Delta G^\circ=-RT\log(K) $$ where $K$ is the equilibrium constant. In dimensional analysis, Bridgman's theorem tells us that the argument ...
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1answer
11k views

Finding molar mass of an unknown acid

"In the titration of a solid acid, an endpoint is reached after 22.0mL of 0.120 M $\ce{NaOH}$ has been added. Assuming that each acid particle contains two acidic hydrogens and both are ...
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1answer
2k views

Why is the carbon dioxide we exhale transparent?

Why is carbon dioxide that comes from dry ice opaque and smoky while the carbon dioxide that we exhale transparent?
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224 views

Oxidation number and Pourbaix diagrams

In a Pourbaix diagram (E-pH diagram) where the regions are given , but the assignment of these to the elements we have is not done yet , how can the oxidation numbers helps me out assigning each ...
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1answer
402 views

Consequences of using reagent preserved with sodium azide on gold film

I am running experiments using reagents preserved with 0.1% sodium azide, which are applied to a gold film. Unfortunately, there are very few options for using reagents without sodium azide. I ...
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1answer
372 views

Would concentration of a compound in equilibrium increase even if it's not favored by a volume decrease?

So say I have a reaction where there are x moles of gas on the reactant side, and y moles of gas on the product side, where x>y. The volume decreases, favoring the products side. The textbook I am ...
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1answer
17k views

Determine concentration Using Beer's law

How do you determine concentration of a sample using wavelength and absorbency? Say our wavelength for a sample of Red 40 is 508.50 nm and absorbance is 0.283 when we use 6ml water and 4 ml Red 40. ...
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2answers
698 views

How would I write an input Lammps command for continuous change in temperature? [closed]

I'm going to study the thermal expansion of graphite. For this goal, I should change the temperature continuously. But I do not know how to code it by Lammps?
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1answer
3k views

Why doesn't diffusion take place between immiscible liquids?

If we take a test-tube of bromine and invert an upside-down test tube of air on top of it, it'll diffuse with the air, until the bromine is thoroughly 'mixed' with the air in both test tubes. But why ...
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2answers
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Azeotropes and separation by distillation?

I have just recently learnt the theory of fractional and normal distillations and the basics of maximum and minimum boiling azeotropes. Most books say that the components of the mixture forming an ...
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1answer
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Equivalent weight of metal [closed]

A metal oxide contains $60$% metal.The equivalent weight of metal is (1) $12$ (2) $60$ (3) $40$ (4) $24$ I know that the equivalent weight of metal oxide = equivalent weight of metal + 8.But how ...
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1answer
81 views

Reaction with carbon

Usually maximum time we see then after cooking by gas there is no black spot on the pot. But continually burning can affect the pot surface and makes black powder. My question is: What is the ...
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2answers
850 views

Bond of interest

What does it mean for our bond of interest if we have low bond length and high frequency? Trying to make this connection but am not understanding. If anyone could explain it intuitively, that would be ...
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1answer
173 views

What does this scale mean?

$$\log_{10}~\mathrm{pg}/\mathrm{ml}$$ I do not understand the scale. How do I convert this to a standard concentration (without the logs)?
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1answer
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Why are partial molar Gibbs energy and Gibbs energy per mol equal?

I'm not a chemist, but I need some insight into chemical thermodynamics. In the book that I'm reading (Nevers, 2012), equation (4.28) relates the chemical potential of a pure species to it's Gibbs ...

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