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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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2
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1answer
59 views

How does the process of protein denaturatation work?

I know it's the proteins that somehow change their properties at some temparature. But what kind of change, in terms of molecule-level structure?
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2answers
2k views

What are the physico-chemical processes at play in ironing of clothes?

The process of ironing of clothes removes (to a large extend) the wrinkles that where introduced in the clothes while drying. Obviously this has to be some physico-chemical process that is initiated/...
7
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1answer
998 views

Activity Coefficients from Electrode Potentials

Lets say we want the activity coefficient of $\ce{Cu^{2+}}$ ions in solution. Would we simply setup one half cell of a $\ce{Cu}$ electrode in a known concentration of $\ce{CuSO4}$ and then connect ...
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2answers
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What is the unit of pH?

I'm making some graphs and I have to label the axes. I want to be extra careful and put the units in even though the meaning of $\text{pH}$ is well known. But I have a problem (though a simple one): $\...
4
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1answer
125 views

Quotable Literature for the Enthalpy of a Proton

A proton obviously has no electronic energy, no vibrational and no rotational degrees of freedom. Therefore I think it is fair to assume, that $$H(\ce{H+})=\frac32\cdot \mathcal{R}\cdot T$$ holds for ...
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3answers
3k views

Eutectic Phase Diagram and Lever Rule

A solution having composition $p$ (left side of graph) is cooled to just above the eutectic temperature (point $s$ is at $0.18$ $x_{\ce{Si}}$ and the corresponding tie line intersects the liquidus ...
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1answer
313 views

How will the pressure of a gas in manometer change if it goes to a place with higher pressure?

Imagine a manometer where air pressure is $\pu{0.8 atm}$ and the gas pressure is more. We move it to sea level which the air pressure is $\pu{1 atm}$. How will the gas pressure change? (the ...
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2answers
2k views

What kind of equilibrium constant we use for Gibbs free energy and Van't Hoff equation?

We know that the Gibbs free energy is related to the equilibrium constant by the following equation: $$\Delta_\mathrm{r}G^\circ=-RT\ln K$$ We also know the Van't Hoff equation: $$\ln\left(\frac{K_2}{...
3
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3answers
1k views

pH and materials selction [closed]

I working on the Navy study guide for their nuclear engineering programs and I am not a Chemist. Thus, I have come here to try and develop a better understanding of the subject matter. Why is pH ...
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1answer
1k views

endothermic dissolution process

Can anybody give me an example of an endothermic dissolution process, preferably one in which name of the substances involved are easy to remember. I have searched the Web thoroughly but could not ...
2
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0answers
178 views

What was the misconception about the search of Philosopher's Stone and how does modern chemistry deals with this topic? [closed]

I just read about Alchemy. And it seems to me that many of their principles are closely related to chemistry. So, here is my doubt - Why is not possible to make that alchemist stone called ...
26
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1answer
17k views

What is the pKa of the hydronium, or oxonium, ion (H3O+)?

Although the wikipedia page on Hydronium indicates a $\mathrm{p}K_\text{a}$ of −1.74, I noticed in the discussion of this page that the subject seems debated (cf. http://en.wikipedia.org/wiki/Talk:...
3
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1answer
699 views

How to estimate the dielectric constant of a liquid?

Are there any approximate relationships between the (static) dielectric constant of a liquid and properties of the individual molecules? For example, suppose I know the polarizability and dipole ...
1
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1answer
818 views

What is the energy change of ethene reacting with hydrogen gas?

$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$ Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF ...
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2answers
2k views

Reaction Pathways: What to do when IRC geometries are relaxed (optimized) and the energy changes significantly

The Story: Reaction pathways can be difficult things to deal with using electronic structure methods. Intrinsic reaction coordinates (IRCs) can be determined a number of ways (a discussion of these ...
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1answer
1k views

Determine standard enthalpy of formation of salt given other reactions

I'm a little confused by this question, perhaps my understanding of enthalpy isn't as good as it should be. For the compound $\ce{KNO3}$, which of the following reactions is used to determine the ...
30
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1answer
2k views

Is there an energy cost associated with flipping the spin of an electron?

THE STORY: A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves. RHF enforces electrons to be paired into spin ...
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1answer
238 views

Why isn't ΔG equal to zero for this equilibrium reaction?

In the reaction $\ce{E(g) <=> P(g)}$ at 25 °C, equilibrium is reached when the pressure of the product is 0.100 that of the reactant. What is $\Delta G$ in joules? Using $\Delta G = RT\ln K$, ...
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2answers
4k views

Hygroscopic behaviour of DMSO - how bad is it?

For a fluid flow experiment I am using DMSO (dimethylsulfoxide), because of its low volatility, reasonably high surface tension, low viscosity and relative safety. In the MSDS of DMSO I find that the ...
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1answer
69 views

Is there any way to use syringe pumpe in pumping flow

I want to use syringe pump to pump water at 0.82 ml/min for 30 min ? Is that possible ( I read some paper use that but don't know how ?)
0
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1answer
100 views

What exactly happens to mass during deuterium fusion?

I know that the mass of Helium-4 is slightly less than the mass of 2x Deuterium it may be made of and that it is the reason fusion gives a lot of energy. But where exactly is this missing mass taken ...
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2answers
3k views

Do lithium and beryllium want to lose electrons to be like helium?

I can't seem to remember. I know that they all want to fill their valence shells, but, aren't these different?
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3answers
24k views

Boiling point of a liquid increasing with temperature?

In my textbook, a statement is given, as follows: Boiling point of a liquid increases with increase in temperature However, I was wondering, isn't this wrong? The boiling point of a liquid always ...
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1answer
4k views

What is the product of CO + 2H2 under normal pressure?

Under the pressure of $\pu{340 atm}$ $$\ce{CO + 2H2 <=> CH3OH}$$ But what is its product during normal pressure of $\pu{1 atm}$? I think it would be a single displacement reaction $$\ce{CO +...
5
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1answer
1k views

Correlation Diagram Doesn't Match Selection Rules?

From Miessler's Inorganic Chemistry, 5th edition, there is this correlation diagram for $d^{2}$ in a octahedral field. On the left hand side, if it's not clear, it goes (from lowest to highest): $^{...
4
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1answer
12k views

Incomplete Combustion products

In class we performed an experiment which I am unable to understand the results for Why does the the amount of soot produced vary? What is the amount of soot produced dependent on? Experiment: ...
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1answer
922 views

Testing a sodium aluminate solution

I prepared some sodium aluminate by reacting a strong $NaOH$ solution with aluminium foil and filtering the result. I now have a clear solution and I'm not sure what it is. I stopped adding aluminium ...
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4answers
2k views

Role of heat in combustion

What role does heat play in the combustion process.Specifically, does the amount of heat determine whether complete or incomplete combustion occurs, and is the amount of heat impacted by the amount ...
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1answer
766 views

Can an excessive reactant amount result in a longer reaction time?

I am performing an experiment with DTZA and Ferrate. After a point of increasing the DTZA concentration too much the Ferrate takes longer (lower reaction rate) to react with the DTZA. Is this ...
4
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1answer
594 views

Most common material in the universe

I was told that 'water' was the most common material in the universe and I disputed that claim. I was met with the argument that hydrogen and oxygen were the most common atoms in the world so water ...
3
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1answer
7k views

Calculate the moles of acid and conjugate base needed

Question Using the following salts listed below, calculate the moles of acid and conjugate base needed to make $V = \pu{100 mL}$ of $c = \pu{0.50 M}$, $pH \in 6.5, 6.7, 6.8$ phosphate buffer ...
3
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1answer
159 views

Low-volatile liquids that 'ball-up' on siliconoxide or perfluoroalkanes

This is a very simple and short question. I am looking for liquids that are low/non-volatile at 20$^\circ$C (at least substantially less volatile than water) which have a high contact angle with glass ...
0
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2answers
145 views

What purpose do chain reactions serve?

I just learned what chain reactions are, but I can't seem to wrap my head around them because it seems utterly useless and doesn't accomplish anything. At least that's how I understood it because the ...
3
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1answer
701 views

Conservation of angular momentum in electronic transition

My book says the "angular momentum is always conserved in a transition". But if suppose we have a s electron then it's angular momentum is $\hbar\sqrt{l(l+1)}+\hbar\sqrt{s(s+1)}$ $\implies \hbar\frac{\...
4
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2answers
1k views

Why Ionic compounds dissolve into water

First, I would like to say that I understand the basic idea of disassociation and solubility. However, as I study intermolecular forces I feel like this basic Idea is being challenged. My ...
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1answer
188 views

What are the products of the thermal decomposition of potassium cyanate with carbon at elevated temperature?

What are the products of the thermal decomposition of potassium cyanate ($\ce{KOCN}$) with carbon ($\ce{C}$) at elevated temps ($\ce{300^\circ C - 1300^\circ C}$)? I guess some of the nitrogen is ...
4
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1answer
655 views

Phase transition from gas to solid

Question 13 from the ACS chemistry olympiad exam: The phase transition from gas to solid is called \begin{align} &\text{(A) condensation.} & \text{(B) evaporation.} \\ &\text{(C) ...
3
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1answer
191 views

Symmetry of an in-phase and an out-of-phase wavefunction “approaching” each other in an MO

Hiho. I have a question concerning this image (Chemistry, Catherine E. Housecroft et al., Pearson Education, 2010). In the text, it states the following: "Each of the new molecular wavefunctions, ...
4
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2answers
18k views

Ground state electron configuration of chromium [duplicate]

What is the ground state electron configuration of chromium? Is it $\ce{[Ar]}4s^23d^4$ or Is it $\ce{[Ar]}4s^13d^5$
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2answers
206 views

What are some examples of a clear, liquid, UV photoactive polymer?

Something that is not reactive to lesser wavelengths of light, specifically IR.
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1answer
87 views

Is there a way to get hot water without altering plumbing or electrical wiring too much?

Is there a way (other than collecting water and heating it on the stove ) to get hot/warm water from the tap without having to alter existing plumbing or electrical wiring ? Perhaps use a chemical ...
8
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1answer
11k views

Why does the equilibrium constant depend on the temperature but not on pressure and concentration?

According to my textbook (and intuitively) certain changes when the aforementioned 3 variables are altered occur in accordance with Le Chatelier's Principle. However, what I don't understand is what ...
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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 ...
4
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1answer
349 views

calculating Kp with partial pressures

This is a question I solved in class: At 35 degrees, $\ce{N_2O_4}$ is 15% dissociated in a flask at a pressure of 1.2 atm. Calculate $K_p$ Equation: $$\ce{N_2O_4(g)<=>2NO_2 (g)}$$ This ...
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2answers
5k views

Why does the equilibrium constant change on scaling the stoichiometric coefficients of a reaction?

I read in my textbook that if we multiply a chemical reaction by some factor(let's say $b$) its new equilibrium constant becomes $K^b$.But I don't understand why this happens.. What is the difference ...
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4answers
5k views

Why is the alpha particle called a particle when it is made of four particles?

We know the alpha particle is the nucleus of helium. It contains four subatomic particles - two protons and two neutrons. The protons and neutrons are further made of particles called up and down ...
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1answer
158 views

Reaction Rate Limiting Reaction

Why exactly does the slowest reaction limit the instantaneous rate of a reaction even if the faster processes come after? Theoretically, if the products of the slow reaction are required for the fast ...
2
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2answers
127 views

Specific Case of the Rate law

My textbook says that for a chemical reaction with two reactants, $\ce{A}$ and $\ce{B}$ with equation $\ce{aA + bB -> Products}$, where $a$ and $b$ are coefficients, the general rate law is: $\...
3
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2answers
29k views

Half cells: difference between E(cell) = E(cathode}-E(anode) & E(cell) = E(oxidation) + E(reduction)

When do I use each of the above? If I use one or the other they give me difference results. For example, I'm trying to put the Volts into an equation to find standard free energy change. $$\Delta ...
5
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3answers
6k views

Activated Complex Products/Reactants

We know that an activation complex is the temporary unstable compound formed when activation energy is reached. But what dictates whether the products are indeed going to be products or if they become ...