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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5
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1answer
13k 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
939 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
789 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 ...
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622 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 ...
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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 ...
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1answer
162 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 ...
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2answers
146 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 ...
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1answer
726 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{\...
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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
199 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 ...
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1answer
690 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) ...
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1answer
193 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, ...
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2answers
19k 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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208 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
88 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 ...
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1answer
12k 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
276 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
376 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
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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
160 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 ...
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2answers
128 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: $\...
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2answers
30k 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 ...
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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 ...
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1answer
28k views

Redox reaction with hydrogen peroxide with potassium iodide

I think I've managed to write down the correct reaction: $$\ce{H2O2 + KI + H2SO4 -> K2SO4 + I2 + H2O}$$ Now I need to balance this using the ion-electron method in an acidic environment. ...
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2answers
1k views

Boiling-point elevation paradox

This is the boiling-point elevation equation: $$ \Delta\mathrm{T}_{b}=ib\mathrm{K}_{eb}. $$ If we do the limit of the above, for $b\rightarrow\infty$ we find that the boiling-point elevation is ...
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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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2answers
2k views

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
1k 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
14k views

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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3answers
86k views

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
621 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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3answers
957k views

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
215 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
302 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
119 views

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
1k 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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2answers
228 views

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
822 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
52 views

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 ...