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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What is the difference between K and Kp in the equilibrium equation?

In this equilibrium equation, $$K = K_p\cdot (RT)^{-\Delta n}$$ what does $K$ represent in comparison to $K_p$? It seems to me that they both are equilibrium constants, so how are they different?
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compression set of tin catalyzed silicone better than platinum?

Platinum silicone is more dimensionaly stable, it shrinks less when it cures. However, i just need silicone which has good compression set (small change by compression), and perhaps, once they are ...
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Is the atom the smallest particle, which takes part in chemical reactions?

According to modern atomic theory, the atom is the smallest particle which can take part in a chemical reaction. But during the formation of hydronium ion, $\ce{H+}$ ion reacts with $\ce{H2O}$ to form ...
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How do I determine if a process is reversible without numeric information?

How do I determine if a process is reversible without numeric information? It would be nice to know how to determine whether a process is reversible in order to solve problems LIKE this one: A ...
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Deriving The Triple Point Temperature and Pressure as the following expression

$\Delta H_\text{fus}$, $\Delta H_\text{vap}$, $\Delta H_\text{sub}$, as well as ($T_\mathrm l,p_\mathrm l$) and ($T_\mathrm s,p_\mathrm s$), which corresponds to the temperature and vapor pressure of ...
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What stopper will stop HCl fumes?

The local hardware stores actually sell chemicals in recycled beer bottles with plastic stoppers as lids. The bottle of hydrochloric acid I bought is clearly losing gas to diffusion through the ...
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What is the actual reason behind PCl₅ existing as an ionic solid?

Why does $\ce{PCl_5}$ exists in the solid state as $\ce{[PCl_6]^{-}[PCl_4]^{+}}$? What is the problem with it that it doesn't exist in its original form in solid state? Like why isn't it just $\ce{...
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Whose concentration is more 1 molar or 1 molal?

I was reading about concentration terms like molarity, molality, etc. and then I came across a question: which concentration is more: 1M(molar) of solute x dissolved in water vs. 1m(molal) of solute ...
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Where did all the elements come from? [duplicate]

I heard somewhere (I think is was a show called "How The Universe Works") that the big bang was the result of a hydrogen atom and a helium atom. Is this true? If so, where did all the other elements ...
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How do things heat one another? [duplicate]

For example, how does a gas stove heat a metal pot? A combustion reaction between the gas and the air takes place, and this releases energy due to new chemical bonds being formed. Do the atoms in ...
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How can enthalpy change of a system be negative while entropy change is positive?

$$\Delta G = \Delta H_\text{system}-T\Delta S_\text{system}$$ $$ \begin{array}{ccc} \hline \text{Sign of}~ΔH & \text{Sign of}~ΔS & \text{Spontaneity} \\ \hline + & + & \text{The ...
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Why is the volume in this compress gas cylinder constant throughout?

I am stuck on this gas question and its really stressing me out. A compressed cylinder of gas contains $2.25 \cdot 10^3~\mathrm{g}$ of $\ce{N2}$ gas at a pressure of $4.25 \cdot 10^7~\mathrm{Pa}$...
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How can I calculate molality from molarity?

How can we determine the boiling point of 1 molar aqueous solution (density 1.06 g per ml) of KBr? If I use the colligative property formula than I require molality instead of molarity. Here the ...
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Weighted Drilling Fluid Comparison with CaCl₂

I asked a question previously, and the answer was quite illuminating. The answer ushered me forth in a direction that finally made sense. I ended up finding this website, chem.latech.edu/~ramu/cmen522/...
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Salts that are more hydrophilic than NaCl

What other, rather easy to obtain, salts are more hydrophilic than $\ce{NaCl}$? Is there a hydrophilic scale for substances like the Mohs scale of mineral hardness?
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1answer
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Pseudo 1st order Kinetic reaction

The pseudo 1st order reaction happens when one of the reactant is in large excess and its concentration doesnt change during the reaction . Is there any other such situation when a certain higher ...
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Can powdered beta-tin be made from raising the temperature of alpha-tin?

When white tin ($\beta$-tin) is cooled to a temperature below $13.2\ \mathrm{^\circ C}$, it creates the allotrope of gray ($\alpha$-tin), a gray, amorphous powder. My question is that once you have ...
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Interaction between soy milk and coffee producing bubbles

I noticed when I poured my soy milk (which I shook as per the directions on the carton) into my coffee, a large number of very fine bubbles rose to the surface. What causes this? Is there a chemical ...
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How do I calculate the pressure of a known liquid in a sealed container heated above boiling point?

If I have water in a sealed container heated to say 150 degrees, how do I determine the amount of pressure being generated in the container? What about for other liquids? I have searched extensively ...
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How do I utilize Henry's Law Constant?

I have tried for several hours to answer this question with no luck. I believe I may be missing a couple of steps or I am not utilizing the given information properly. Nonetheless, some guidance will ...
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1answer
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Is there a relationship between bond strength and polarity?

I believe that a more polar bond would be stronger, since it would be similar to an ionic bond. However, this seems to be wrong when applied to the study of acidity of some compounds.
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Interpreting X-ray diffraction data [closed]

So I've got my data for some x-ray crystals of small molecules of Ag, Cu,... I was curios to know what the best way to determine what type of lattice each of these atoms may have?
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In a monomolecular reaction, how can a reactant experience collision to react?

Monomolecularity means no molecules which experience collision with each other taking part in reaction. So how it is possible that in monomolecular reaction only one reactant experiences collision?
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Chemical potential of mixtures

I feel that there are very few textbooks that treat the chemical potential of mixtures in an understandable clear way, which is why I wanted to ask here about certain things. Although I do not have a ...
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1answer
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Entropy - Negligible?

In electrochemistry, the Nernst equation tells us the cell potential for non-standard conditions. I read that the factor $\frac{-RT}{nF}\ln{Q}$ accounts for difference in cell potential due to ...
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2answers
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Rate constant and Michaelis Menten

Please consider the following figure of a concentration over time (msec) diagram with variables for an enzyme, a substrate bound enzyme and a product. Recall that $\ce{E + S \leftrightharpoons ES \...
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Can we force a reversible reaction in equilibrium to achieve 100% completion?

Can we force a reversible reaction in equilibrium to become a "complete" one? If so, will the equilibrium constant change? It's said about reversible reactions that they never go to completion & ...
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1answer
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How does an ice bath change the rate of an reaction?

If I had hydrogen peroxide decompose with the help of manganese dioxide and measured the time taken for the reaction to complete and the volume of oxygen collected. I will get a graph that looks like ...
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1answer
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What is the difference between the Joule and Joule–Thomson coefficients?

Is there a difference between the Joule coefficient and the Joule–Thomson coefficient? Also, I am having a hard time understanding what they mean.
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How to calculate a rough estimate for the volume of a nitric oxide molecule?

I was wondering what would be the best way to calculate a rough estimate for size of a nitric oxide molecule to use in comparison to a box. I was thinking volume would be the best method, but this ...
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Why did they provide the value for the enthalpy change of fusion?

The metal gallium melts when held in the hand; its melting point is $\pu{29.76 ^\circ C}$. How much energy as heat is removed from the hand when $\pu{5.00 grams}$ of gallium initially at $\pu{20.0^\...
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Oxide surfaces develop a charge in H2O. Do we have any, even vague, handle on how long does an indivdual charge last on avg. before being neutralised?

We often know, from e.g. titration experiments, what the average surface charge density of a surface is. How do these charges vary over both time and space (i.e. dynamics)? I have been unable to find ...
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Can you find the mass of solvent with mass of solute, volume of solution, and solution density?

If you have, for example, $\pu{10 g}$ of a solute dissolved into $\pu{100 ml}$ of a solution, and the solution density is $\pu{1.5 g ml^-1}$, can you just multiply $100\ \mathrm{ml} \times 1.5\ \...
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1answer
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Can an emulsion be emulsified?

Can clusters of an emulsion be emulsified into another emulsion? If so is there any common product or natural substance that would have such a structure? Finally is there a name for this? I looked ...
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1answer
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Calculating the ionization energy for hydrogen

What energy would be needed to remove the electron from the $n = 4$ level of the hydrogen atom? $\pu{−3.49 * 10^{−17} J}$ $\pu{−1.36 * 10^{−19} J}$ $\pu{+2.18 * 10^{−18} J}$ $\pu{+1.36 * ...
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How do I excel in Chemistry? [closed]

I wanted to ask an online group of experts/community about how I could improve in chemistry. I study in 10th grade currently and don't get very good grades. Most of the time its a B or C. I have to ...
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2answers
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Redox reaction with tin and sulfuric acid solution

I need to write the redox reaction from tin and a sulfuric acid solution. Here is the solution given: The first half-reaction: $\ce{Sn->Sn^2+\+2e^-}$ The second half-reaction: $\ce{2H+\+2e^--&...
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1answer
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Which solvent is good for using SU-8 particle in Optical tweezers?

I'm studying Optical tweezers. I've used Polystyrene for samples. Nowadays, I've got SU-8 pillar. I wanna use that for sample, but its density is heavier than water. I can't use that. So I wanna know ...
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Can magnetic fields affect a chemical reaction?

This question was asked recently in an interview and I just said that "Yeah, like if the reaction involves ions or paramagnetic species". But the interviewer went on and asked me to elaborate on HOW ...
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Reaction Kinetics and Stoichiometry — Mass conservation

This question has been bothering me for some time, and I can't seem to find a good answer online. Say I have four chemical species $\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$, and these four react in the ...
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Why is beryllium transparent to x-rays?

Beryllium has other fancy applications. It is transparent to x-rays, so it's used in the windows of x-ray tubes, which need to be strong enough to hold a perfect vacuum, yet thin enough to let the ...
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Predicting rate equations from data

I am having trouble wit the following question on my problem sheet: "The reaction $\ce{Br- + ClO^- \to BrO^- + Cl^-}$ occurs with a rate constant of $\text{0.35 dm}^3 \text{mol}^{-1} \text{s}^{-1}$ ...
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1answer
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The Workings of Pulse-Height Discrimination

Pulse-height discrimination is a common technique to filter out unwanted background signals from the analytical signals. But how exactly does it work? The analytical signals are not continuously ...
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Second order reaction half life equation?

For the reaction: $$2A\to p$$ The rate, $v$ may be given as: $$v=-\frac12\frac{d[A]}{dt}=k[A]^2$$ Correct? Integrating this gives: $$-\frac12\int_{[A]_0}^{[A]}\frac{d[A]}{[A]^2}=k\int_0^tdt$$ $$\...
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Does the speed of an ion affect the current that can flow through a solution?

Typically, when a cathode and anode are inserted into a solution that allows current to flow, the ions are moving with a certain kinetic energy. If the ions were to gain kinetic energy (through ...
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Why are potentials of cells with magnesium electrode always lower than expected?

I have prepared the 1M water solution of magnesium acetate. Then I placed $\ce{Mg}$ and $\ce{Cu}$ electrodes in it. I predict there such reactions take place: $$\ce{Mg-2e^- \rightarrow Mg^{2+}}$$ $$\...
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1answer
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How to make sense of the 'Relaxation Method' for measuring reaction kinetics?

I get the concept that one can measure the rate of reaction by measuring the rate at which an equilibrium state reaches another equilibrium state after the system is perturbed (usually by heating). ...
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1answer
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Would solar panels produce energy if uniform temperature in the universe? [closed]

If the temperature on the surface of the sun and on the surface on the earth were the same, and the temperature of the universe were uniform, would the solar panels produce energy?
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What's the difference between perfect and ideal gas?

There are all kinds of different dinstinctions in the internet, and I'd like to see what you guys thought. Actually, I've been asked if the heat capacity of an ideal gas es independent of temperature....
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How to calculate the pressure of an ideal gas that undergoes isothermal expansion?

A 2.35 mole sample of an ideal gas, for which $C_{\mathrm{m},v}=3R/2$ initially at $\pu{27 ^\circ C}$ and $\pu{1750 kPa}$, undergoes a two stage transformation. For each of the stages described in the ...

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