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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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2answers
3k views

Do catalysts undergo physical changes during a reaction?

I know that catalysts don't undergo chemical changes during a reaction, but do they undergo physical changes? If they do, are there any examples?
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How many moles of the substance are in 2.5 g of lead?

How many moles of the substance are in 2.50 g of lead? What I did: Atomic mass of Pb: 207.2 amu (or g?) Applying unitary method, 1 mol of Pb -> 207.2 g; so, x -> 2.5 g $x = \frac{2.5}{207.2}= \pu{...
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1answer
961 views

Why does helium seem to exhibit an ionization energy affected by the shielding of electrons?

According to Wikipedia, the shielding effect only happen in atoms which have more than 1 electron shells. The core electrons repel the electron in the valence shell. However, I have heard some ...
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2answers
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Finding the average rate of consumption

The question is: If $2.0 \cdot 10^{-4}$ moles of dye in $50$ mL of solution is consumed in 188 seconds, what is the average rate of consumption of dye in $\text{mol}/\text{L}\cdot \text{s}$? I am not ...
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Angular and radial nodes

Nodes are the points in space around a nucleus where the probability of finding an electron is zero. However, I heard that there are two kinds of nodes, radial nodes and angular nodes. What are they ...
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2answers
566 views

Why does the cathode ray tube only start glowing at low pressures?

I am considering the cathode ray tube of the set up, when the cathode rays were discovered: Voltage = very high Gas = any Atmospheric Pressure = changing At different pressures, there are different ...
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What are the maximum number of electrons in each shell?

In my textbook, it says that the maximum number of electrons that can fit in any given shell is given by 2n². This would mean 2 electrons could fit in the first shell, 8 could fit in the second shell, ...
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1answer
210 views

Evaporation velocity of ethanol: adding ethanol vapour to a gas mixture

I need to add a known amount of ethanol vapour to a gas mixture (He/Ar). To do that I let the mixture bubble in liquid ethanol kept at a known temperature (14 C). The system is made of a large steel ...
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1answer
4k views

Is melting of NaCl a physical and chemical process?

If I melt $\ce{NaCl}$, I get a molten salt. This means a liquid formed only by ions ($\ce{Cl^-}$ and $\ce{ Na^+}$). That could mean that the crystal $\ce{NaCl}$ experimented a chemical change: $$\ce{ ...
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1answer
74 views

Polymers with no molecular mass distribution?

What sort of ideal conditions are required - theoretically - to conduct polymerization reactions to make all the macromolecules end up with exactly the same molecular mass, just like the products in ...
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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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0answers
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Why does confinement of quantum dots result in discrete energy levels?

I'm doing a project with lead (II) sulfide quantum dots because they have optical transitions in the near infrared. I understand the simple "particle in a box" approach where confinement strengthens ...
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1answer
1k views

What is the reason a grain of salt alters the perceived bitterness of coffee by such a high degree?

Coffee served hot can be quite bitter (presumably high pH). Several people I have known will add a single grain of salt to the coffee - which reduces the perceived bitterness. My question is: What ...
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2answers
8k views

What are the main differences of CTAB and DTAB surfactants? And what are practical applications of them?

Just doing a little bit of research of both surfactants but I can't seem to find too much online about them. Hopefully you guys can help out!
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3answers
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How is langmuir's adsorption isotherm different from Freundlich's

I see no difference between the two,both say that degree of adsorption reaches a limiting value at high pressures and at very low pressures degree of adsorption is directly propotional to pressure. ...
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1answer
108 views

Does anyone know where I can find the reaction rate coefficient and design equation for the electrolysis of brine and sodium hydroxide solution?

equation 1) $\ce{2 Cl^{–} -> Cl_2 + 2e^{-}}$ equation 2) $\ce{2 H2O + 2 e^{–} -> H2 + 2OH^{–}}$ These equations are the key reactions in the chlor-alkali process. I want to model a reactor ...
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1answer
2k views

Thermal decomposition of calcium carbonate

Thermal decomposition of calcium carbonate. In general, we heat $\ce{CaCO3}$ to temperature of approximately 825°C it decomposes into calcium oxide and liberates carbon dioxide gas:* $$\ce{CaCO3} \...
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1answer
997 views

How do I calculate the enthalpy change when a gas is being used to heat water?

The question I'm trying to answer is: Calculate the mass of butane gas that would be needed to heat $724\ \mathrm{cm^3}$ of water from an initial temperature of $7.44\ \mathrm{^\circ C}$ to $50.7\...
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For a given teabag and dunking duration - will I get more caffeine in a bigger cup or the same amount?

When choosing a cup of tea, I can choose a big cup or a small cup. I'm wondering if I get more caffeine with the bigger cup or the same amount of caffeine. (in moles) My question is: For a given ...
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1answer
709 views

Finding the final temperature

If $125$ Calories of heat is applied to $60.0\text{g}$ piece of copper at $21.0^\circ\text{C}$, what will the final temperature be? The specific head of copper is $0.0920 \text{ cal/gC}$. All I have ...
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4answers
6k views

Why do solutions become saturated?

Why can a solvent dissolve only a particular amount of solute? If we add more solute to the solution, the number of solute particles in contact with water increases. So rate of dissolution should ...
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1answer
4k views

Equilibrium calculation gives negative molarity

There is a reaction: $$\ce {ClF3 <=> ClF + F2}$$ with $\ce {K_\mathrm{c} = 2.48 x 10^{-3}}$ Initially, $\ce {[ClF3] = 0.25 M} $, $\ce {[ClF] = 0.031 M} $, and $\ce {[F2] = 0.02 M} $. $\ce {F2}$ ...
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1answer
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Z:#Neutrons Ratio

Is there a fixed ratio that can be used to calculate the number of neutrons in the nucleus of the most stable isotope of an element by knowing the atomic number? Side question: if Z is the symbol for ...
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1answer
232 views

Why is the maximum % for a gold alloy 92%?

The assignment question is asking us to explain why you can't get more than 92% gold in a gold alloy, and I can't seem to find out why it's specifically 92% in either the textbook or online. Any ...
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2answers
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How does molecular structure affect physical properties?

The question sounds vague and non-specific because my background in chemistry is limited to undergrad college courses. However, I am interested in learning the correlations between the atom-by-atom ...
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5k views

Does rate of Evaporation change with surface area?

Two vessels of the same volume, in the same location and open to the atmosphere. One is of a small diameter, the other is of a larger diameter. The question is will the vessel with the larger surface ...
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2answers
1k views

Solubility, pressure and Henry's law

Determine the solubility of $\ce{N2}$ in water exposed to air at $\pu{25^\circ C}$, if the atmospheric pressure is $\pu{1.2 atm}$, assume that the mole fraction of nitrogen is $0.78$ in air and the ...
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1answer
376 views

What does the negative superscript in the term symbol for ground state Oxygen stand for?

I think that I understand most of the parts of the symbol shown for ground state oxygen $\ce{{}^{16}O2}$, which is ${}^{3}\Sigma^{-}_{g}$. However, I was hoping that someone could tell me what ...
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1answer
174 views

Nature of transition metals [duplicate]

The transition metals have valence and penultimate shell incompletely filled . so does this mean that the transition metals first fill up their valence shell and then penultimate shell?
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5answers
9k views

The last element's atomic number

I was just thinking what can be the last atomic number that can exist within the range of permissible radioactivity limit and considering all other factors in quantum physics and chemical factors.
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2answers
64k views

What is the differences between partial pressure and vapour pressure?

Was looking at Henry's law and Raoult's law constants and there seemto be lots of equations involved. Henry's law involves partial pressure and the latter involves the vapor pressure. Wondering what ...
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2answers
404 views

To which state of matter does the flame belong to?

I had this question from the day (9 years old, now 16) that I learned about states of matter. I have asked many of my teachers, some of them told me it's a gas some that it's a plasma. Can anyone ...
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What is the nature and character of fire? [duplicate]

What is fire? Is it a material or energy or something else? Please explain it to me. My friend asked me this. I am stuck with this problem.
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1answer
122 views

Why is the pressure value altered in this gas law numerical?

When I work through the following problem it is unclear to me why 0.00120 mmHg is converted to 0.00332 mmHg. What is the temperature of 0.00332 g of mercury in the gas phase with pressure of 0....
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1answer
3k views

How do I determine crystal field splitting (for example, for [Ni(CO)4])?

How to know how many electrons are there in $T_{2g}$ and $E_g$ orbitals? I think rather than a broad answer, an example would help. So, consider the compound $\ce{Ni(CO)4}$ and how to calculate CFSE ...
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2answers
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What is the pKa Range for weak acids and bases?

Am I correct in assuming that the following is true? $\mathrm pK_\mathrm a < 3$ is for a strong acid $3 < \mathrm pK_\mathrm a < 7$ is for a weak acid $7 < \mathrm pK_\mathrm a < 11$ ...
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1answer
227 views

What can I use as a sacrificial electrode to stop the oxidation of aluminium?

For a solution of chromimum phosphate when putting in to solution aluminum there is removal of the aluminum. It is possible to prevent a galvanic cell, stop the etching of the aluminum, by putting ...
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3answers
1k views

Alternatives to Ring Stands

I'm trying to find an alternative to simple ring stands to hold a simple electrochemical cell. The issue is that it is difficult to adjust the height to the right position to within even a couple ...
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1answer
147 views

Do the compounds NaₓIrO₂ and NaOsO₂ exist?

Based on some physics background, I want to know whether have scientists synthesized these two materials: $\ce{Na_{$x$}IrO2}$ and $\ce{NaOsO2}$ in the lab, if so, what properties do they have? I ...
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1answer
201 views

Ideal gas derivations

For an ideal gas, how can someone obtain this: $$ \bar{V}dP = RdT- P \bar{dV}$$ from which it can de deducted, that for a constant temperature $$ \frac{dP}{\bar{dV}} = -RT $$
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2answers
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What type of sensor technologies exist to determine the chemical composition of a polymer?

Let's say I have several pieces of trash and each is made with a different type of material like: Plastic bottle : High Density Polyethylene (HDPE) Cereal box : Paperboard & Epichlorohydrin ...
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5answers
24k views

Why does ZnO turn yellow when it is hot?

Why does ZnO's color become yellow when it is hot? I have read that it is because of physical properties, but I need a more elaborate explanation.
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How do I distinguish between internal energy and enthalpy?

I am finding it hard to distinguish between the two. Can someone explain the two terms and the difference between them? I tried learning from Wikipedia, but it said for both the above terms that it ...
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3answers
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Why is the enthalpy change not zero in an adiabatic process?

Which of the following must be true for adiabatic processes? $C_V = C_p$ $\Delta H = 0$ $\Delta U = 0$ $\Delta S = 0$ $q = 0$ (Source: Chemistry GRE) The answer is $q = 0$. From ...
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1answer
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Could micrograms of polonium really change the viscosity of a whole teapot?

I was reading How radioactive poison became the assassin’s weapon of choice and it opens describing how The men eventually left, and Andrade cleared the table. As he poured the remaining tea away, ...
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4k views

What makes substances explosive

Can someone explain clearly to me why some things are explosive?
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1answer
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Why do bubbles form when it rains?

I noticed sometime ago that bubbles formed in puddles/streets whenever it rained. I am wondering if someone could tell me what could cause such bubbles. I examined the bubbles again today more closely ...
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3answers
2k views

Can an aqueous solution conduct electricity forever?

We know that pure water does not conduct electricity, but salt water is a decent conductor. This is commonly explained by saying that “the ions carry the current through the solution”, which is an ...
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1answer
143 views

Viscosity of two different solutions

Suppose that I have 10 kg of plastic/polymer that is non solvable in water. I then divide the plastic/polymer into two equal parts. Let us name the parts A and B in order to identify them. I then ...
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1answer
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Is it realistic to have a natural oxygen source in a cave?

Is it realistic to have a natural oxygen source in a cave? I am writing a story, about people who live underground in a land that is freezing outside. Heat is taken care of by geothermally heated ...