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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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1answer
222 views

Effect on rate of diffusion in addition of an inert gas

What will be the effect on the rate of diffusion on addition of an inert gas to the gaseous mixture? I think the rate of diffusion should increase as the addition of extra gas will increase the ...
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1answer
54 views

How to determine if pressure surpasses capacity with the van der Waals equation of state?

I have to decide whether a $\pu{20 L}$ container with $\pu{0.8 kg}$ ethane can withstand the pressure at $\pu{373.15 K}$. The following information is given: \begin{align} b &= \pu{6.448x10^-2 ...
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1answer
276 views

Dependence of Van der Waal's constants with distance

Shouldn't the constant change as the intermolecular forces vary at different distances? Or is it the case that the constants have nothing to do with the forces because we are using the 4 gas laws i.e ...
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2answers
272 views

What is the exact relationship between the Pi conjugated bonds in organic molecules and fluoroscence of those molecules?

Some compounds are more fluorescent than others, and some of those are Rhodamine, Phenolphtalin, naphthalene, anthracene etc. I want to know why these exact molecules undergo such phenomena, what is ...
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1answer
963 views

How does electrolytic conduction depends on the size of ions & their solvation?

The textbook says, The smaller the effective size of the ion after solvation, the greater will be its conducting power." But, on the Internet, it is explained as follows: Radius decreases, ...
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1answer
4k views

Graph between PV & P, Boyle's Law and its interpretation

My text book says: At higher constant temperature, the volume increase and value of product PV should increase due to increase of volume at same pressure, but PV remains constant at this new ...
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1answer
246 views

Why must NaOH be in excess if we wish to measure the effect acid strength has on the enthalpy of neutralisation?

A few different acids are given i.e $\ce{HCl}$ , ethanoic acid, $\ce{H2SO4}$, ethanedioic acid. We want to conduct an experiment in which we measure the temperature rise for neutralisation as a ...
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1answer
878 views

Calculating Boiling Point of solution

I wish to calculate the boiling point of the following solution. (w/w) 78.8% Glycerol, 11.6% Propylene Glycol, 8.3% Water, 1.2% Nicotine (molar fraction) 0.5790 Glycerol, 0.1037 Propylene Glycol, ...
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1answer
81 views

If an atom of any element gained energy, does it always mean that its electrons gain energy too?

My book says ; "The transitioning of electrons in atoms from one energy level to another is associated with changes in the energy of the atom." But it hasn't made it clear whether or not the gaining ...
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1answer
847 views

Using Mathematica to Plot an Isotherm at its Critical Temperature

Hello I'm new to mathematica and I have been trying to plot an isotherm for a substance at its critical temperature, using Van der Waals equation of state. I have done all the work except I do not ...
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2answers
129 views

How to obtain saturated pressure of water at 200 ºC using fugacities?

The target is to obtain saturated pressure of water at $\pu{200 ^\circ C}$ using PHI-PHI (fugacity coefficients) approach, so it means it's a VLE of water only, so we write equilibrium condition: $$...
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1answer
69 views

Molecular Geometry [duplicate]

Why is it that for a molecule with trigonal bipyramidal geometry, the lone pair is located in the equatorial region whereas for a molecular with an octahedral geometry, the lone pair is located in the ...
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1answer
135 views

Calculating cell-potentials

I have measured the cell potential between a number of metals e.g. Ni, Pb, Al, Cu and Zn by constructing a galvanic cell and then used a voltmeter to measure the potential. Now, if I want to ...
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2answers
550 views

Ordering compounds by boiling points

Here is a MC question from my chemistry professor: What is the correct order of boiling points for molecules: $\ce{CO2}$, $\ce{LiOH}$, $\ce{CH3OH}$, $\ce{CH2O}$? I am mainly confused about ...
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1answer
905 views

Please help regarding finding the correct approach {solid states}

In Diamond, carbon atom occupy FCC lattice points as well as alternate tetrahedral voids. If edge length of unit cell is 356 pm then diameter of carbon atom is ________? I got the answer but is it ...
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1answer
242 views

Where does the extra electron come from in the Lewis dot structure of OH-? [duplicate]

Hydrogen has one valence electron and oxygen has 6 valence electrons. However, the dot structure shows 3 lone pairs of oxygen and 1 shares with hydrogen.How is that possible?
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2answers
2k views

The Thomson wheel experiment

JJ Thomson did an experiment with discharge tube using hydrogen gas. Later it was found that anode rays and Cathode rays both exist at the same time.. Cathode rays move opposite to anode rays. My ...
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2answers
212 views

is there any boundary or membrane around atom to recognize its shape?

we know that every Isolated atoms are spherically symmetric.how we know its shape, is there is any membrane covers it as skin of our body?
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2answers
577 views

Why atomic number decreases in alpha emission

My teachers taugh me that alpha particle is a helium nucleus carrying net +2 charge, hence if an radioactive subastance emits alpha particle it looses two of its protons and two neutrons but no ...
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3answers
204 views

How does the vacuum in atoms persist?

From very elementary chemistry I understand that atoms are mostly empty space, with a few tiny little objects whizzing around. There must then be a vacuum in between these particles. I always thought ...
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2answers
98 views

Having a contradiction while deriving Gay-Lussac's law using Boyle's law and Charles' law

From Boyle's law: $$P_1V_1 = P_2V_2 \quad\implies\quad V_2 = \frac{P_1V_1}{P_2} \label{eqn:boyle}\tag{1}$$ From Charles' law: $$\frac{V_1}{T_1} = \frac{V_2}{T_2} \quad\implies\quad V_2 = \frac{...
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3answers
460 views

Why is the enthalpy of a reaction equal to the difference between the enthalpies of combustion of the reactants and the products?

My textbook gives me the following formula for calculating the enthalpy change of any reaction: $$\Delta H_\mathrm{r}^\circ=\sum(\Delta H_\mathrm{c}^\circ)_\text{reactants}-\sum(\Delta H_\mathrm{c}^\...
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2answers
143 views

How can the Brønsted-Lowry theory be valid?

How can an element accept a proton? Isn't this practically impossible? An atom can take an electron and place it in its valence shell to complete its octet or duplet, but, the proton sits back in the ...
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1answer
106 views

Changes in entropy and Gibbs free energy for sublimation at triple point [closed]

The standard enthalpy of sublimation of dry ice (solid carbon dioxide) is $\Delta H=6.03\ \mathrm{kJ/mol}$. The triple point of $\ce{CO2}$ is at $p=5.1\ \mathrm{atm}$, $T=-56.7\ \mathrm{^\circ C}$. I ...
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1answer
34 views

Can polypropylene be separated from polyethylene ? [closed]

What techniques are available for sorting on a large scale?
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1answer
1k views

If copper is insoluble in excess NaOH, does it mean it is soluble in NaOH when not in excess? [closed]

I don't understand, does it mean when i add a little bit of NaOH, there will be completely no precipitate/ it will dissolve?
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1answer
112 views

Deriving Thermodynamics equations confusion [closed]

Please explain: I have taken up to Cal 3 so I understand deriving but I guess because of how it is used in context of this class I am not understanding. In the thermodynamics equation: ( as an ...
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1answer
239 views

why molecules gain energy when heated?

molecules in solid or liquid or gas gain kinetic energy when heated. why is it like this? I request explanation in details please
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1answer
2k views

How to calculate the mass of a component in battery acid based on the density and mass fraction?

Battery acid has a density of $\pu{1.285 g cm^-3}$ and contains $38\%$ by weight sulfuric acid. How many grams of pure sulfuric acid are contained in a liter of battery acid? I just took $1.285 \...
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4answers
143 views

How can one come to know how a catalyst affects a reaction when the reaction and the catalyst is known [closed]

How can I come to know how a catalyst affects a reaction when the reaction and the catalyst used is known. I searched the internet for an answer but could not find one.
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2answers
265 views

Oxyhydrogen applied to a catalytic converter

Recently people have been reporting that if you blow 'HHO' gas (Oxyhydrogen) into a used catalytic converter it gives off excessive heat. Look here for any number of examples. There is a suggestion ...
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1answer
300 views

Radial expectation value for particle in a cubic box [closed]

A hydrogen atom is in a cubic box with side lengths equal to $\require{mediawiki-texvc}\pu{100 \AA{}}$. For what value of $n$ (principal quantum number) will the expectation value of the radius be ...
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1answer
52 views

Why are the phase diagrams showing $G_s$ and $G_l$ situated so close on one end and then widens up at the other extremes? [closed]

With reference to the phase diagrams drawn in b and d why are the Gibbs phase lines coming closer from being so further apart?
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2answers
60 views

Finding the pH of the solution

In this video, at 3:30 min professor solves two equations $$\ce{H2O —> H+ + OH-}$$ and $$ \ce{HCl —> H+ + Cl-}$$ and deduces $[\ce{H+}] = [\ce{Cl-}] +[\ce{OH-}]$. How come this happen from ...
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3answers
51 views

Which of the following options are correct? [closed]

The equilibrium constant $K$ for the reaction $\ce{2HI <=> H2 + I2}$ at room temperature is $2.85$ and at $\pu{698 K}$ is $0.014$. This implies that: a) $\ce{HI}$ is exothermic compound b)...
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1answer
70 views

Getting pH of a weak acid and conjugate base with a given ratio [closed]

A practice question reads What is the $\ce{pH}$ of a solution of a weak acid and its conjugate base when the ratio of the concentrations of the conjugate base/weak acid is 1/3? (the weak acid $K_\...
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1answer
76 views

Celsius to Kelvin [closed]

A temperature conversion question asks the following: "The temperature of a sample of a substance changes from 10°C to 20°C. How many Kelvin degrees does the temperature change?" The correct answer ...
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2answers
234 views

Why does the compound formed after a coordinate bond have a net charge? [closed]

Why does the molecule have net positive charge?
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1answer
71 views

Is there a better model than the Kinetic Theory of Gases [closed]

I'm looking for a better relationship between the Kinetic energy of a gas and it's Temperature, and also how they vary with gravity (not altitude, just gravity!). So is there a model better than the ...
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2answers
1k views

Exothermic and Endothermic reactions stability

We Know that when a system becomes stable,it gives out energy. In case of exo reaction,heat is liberated resulting in energy loss and thereby stabilizing the system. In case of endo reaction,heat is ...
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1answer
843 views

Maximum in Maxwell–Boltzmann distribution [closed]

I need to find the maximum of the Maxwell–Boltzmann distribution $$P(v) = \left(\frac{m}{2\pi kT}\right)^{3/2}4\pi v^2 \exp{\left(-\frac{mv^2}{2kT}\right)}$$ I know that occurs when $\mathrm dP(v)/\...
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1answer
86 views

Uncertainty Theorem [duplicate]

What is the physical meaning of Heisenberg's Uncertainty Principle? We have derived it mathematically but what is the logical explanation for it?
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1answer
624 views

How come noble gases have full outer shells? [closed]

Argon has $18$ electrons overall and $8$ in the outer shell. But the $3^{rd}$ shell is supposed to have $18$ electrons. Please use A-level terms so that I can understand.
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1answer
5k views

Van't Hoff Factor of Sucrose [closed]

What is the Van't Hoff factor for sucrose? According to me it should be 2 as sucrose is a disaccharide.
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1answer
344 views

Why do universal indicators in titration have to be swirled?

Why do universal indicators in titration have to be swirled? Here's a specific example: I am using methyl orange along with hydrochloric acid to test the alkalinity of a set of household cleaners (...
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1answer
167 views

Second law of thermodynamics: How do entropy changes in the system and the environment count in? [closed]

$$\frac{q_{rev}}{T} = \Delta S$$ Here, what does $\Delta S$ signify? Does it mean the change in entropy of the system or the surroundings? How are the entropies of the system, the surroundings, and ...
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1answer
1k views

Calculating the molarity of an acid solution

Concentrated hydrochloric acid is $37\% \ce{HCl}$ by mass and has a density of $1.2\rm~\frac{g}{ml}$. Calculate the molarity of a solution made by diluting $125\rm~ ml$ of concentrated $\ce{HCl}$ with ...
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3answers
39k views

Is the speed of gamma rays equal to the speed of radio waves? [closed]

Does a radio wave or gamma radiation have a faster speed? I know that all light travels at $\pu{3E8 m s-1}$, but does that include these forms of electromagnetic radiation? Or do radio waves travel at ...
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2answers
84 views

What happens when two galvanic cells are placed in series

I understand how a single galvanic cell works, and the relation of equilibrium and the Nernst equation. But this appears to contradict the higher voltage in a series configuration because it ...
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1answer
76 views

How hydrogen molecule is formed? [closed]

How two hydrogen atoms come close to form a bond ? Textbooks refer to a potential energy diagram but what i cant understand is what is this potential energy if the atoms are neutral . How they come ...