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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Using Arrhenius equation to calculate the ratio of two reaction rates

For two reactions, $$\begin{align} \ce{A ->[$k_1$] B} \tag{1} \\ \ce{A ->[$k_2$] C} \tag{2} \end{align}$$ you have determined that the activation energies are $\pu{71.9 kJ/mol}$ for $(...
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1answer
64 views

What is the difference between primitive Hexagonal unit cell and Hexagonal closed packing HCP [duplicate]

There are 14 types of Bravais crystal lattices (Primitive + Centered) in 3D. Every solid in this universe is made by the unit cells of these lattices. With the help of these Bravais lattice can ...
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27 views

Defintion of Solubility in Different cases

How do we define solubility (in moles per liter) in cases when concentration of cation is not equal to the concentration of anion? e.g. When we put AgCN in an acidic solution (Leading to formation of ...
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Oscillation of particle in harmonic oscillator

In harmonic oscillator, as vibration quantum number increases then does the distance of oscillation of particle from the mean position where there is minimum potential energy increases? If yes, then ...
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1answer
34 views

How does electrolytic conductance depend on solvation?

My textbook says: If the ions are strongly solvated their effective size will increase and hence their conductance will decrease P.s after reading my textbook, I don't think I'm sure what solvation ...
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33 views

Measuring vapour pressure in a closed system

My experiment requires the determination of vapour pressure from which I will calculate the number density (or number of moles of the molecule) later, for a closed system. Here's my setup : Liquid ...
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0answers
66 views

Why is E°(cell) not ∆E°cell?

$E^\circ_\mathrm{cell}$ is the EMF of the cell for a reaction with respect to standard hydrogen electrode (SHE). So why don't we represent $E^\circ_\mathrm{cell}$ or $E_\mathrm{cell}$ by $\Delta$ ...
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1answer
215 views

Verb for Sorption

Slightly silly question! Intuitively I want the present-simple verb for sorption to be "sorps", but saying it out loud, "sorbs" sounds much more natural. However, Google doesn't turn anything up for ...
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Overlap integrals in Hückel theory

In Hückel theory we are only interested in π systems, where $\mathrm p_z$ orbitals overlap. One of the approximations in Hückel theory is that the overlapping $\mathrm p_z$ orbitals are orthonormal: $...
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What does “correct orientation” in a chemical reaction mean conceptually?

My chemistry teacher was talking about how there are two requirements for a reaction to occur: The reactants must have enough energy; and they must also have the correct orientation for a reaction ...
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What is the value of isothermal compressibility of a van der Waals gas at critical point?

For a van der Waals gas, isothermal compressibility is $$\kappa=\frac{V^2(V-nb)^2}{nRTV^3-2an^2(V-nb)^2}$$ If one substitutes the values of critical temperature and volume in this formula, isothermal ...
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Finding initial amount of ammonia using equilibrium constant and amount of nitrogen gas

Question When an amount ammonia is added at $\pu{600 K}$ in a $\pu{1 L}$ container the following reaction takes place: $$\ce{N2(g) + 3 H2(g) <=> 2 NH3(g)}$$ The equilibrium constant $K_c = 4.20$...
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Determining standard Gibbs free energy for water?

I am dealing with the dissociation of water into its components hydrogen and oxygen and I am trying to determine the standard Gibbs free energies of each component. My professor said if the substance ...
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Vapour pressure and Boltzmann energy distribution [closed]

As theory says, there is always a certain amount of molecules in a liquid sample which have energies greater than a thresold energy and get free from intermolecular forces in liquid and produces the ...
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1answer
68 views

Does the property of additivity for the amounts of different substances hold up for ideal gas law?

A mixture contains $\pu{8.00 g}$ each of $\ce{O2},$ $\ce{CO2},$ and $\ce{SO2}$ at STP. Calculate the volume of this mixture. Which of the gases would exert the greatest pressure and why? Here is my ...
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Finding Ka of a monoprotic weak acid from pH and concentration of added sodium salt

A solution of $\pu{0.36 M}$ of the sodium salt of a generic monoprotic weak acid $\ce{HA}$ has a $\mathrm{pH}$ value of $8.782.$ $K_\mathrm{a} = ?$ Why doesn't the following formula work in this ...
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1answer
2k views

Enthalpy of the reaction between hydrogen and oxygen

The reaction between hydrogen and oxygen to yield water vapor has $\Delta H^\circ = \pu{- 484 kJ}$. How much $pV$ work is done, and what is the value of $\Delta E$ in kilojoules for the reaction of $...
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77 views

Why does silver stick to the glass in Tollens' test? [duplicate]

Why does it not simply form a solid powder at the bottom of the flask? Does silver also stick to the glass in other silver precipitating reactions? EDIT: My question is definitely not the same as ...
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2answers
64 views

Concentration of gas above aqueous ammonia

I am a physicist who has run into some chemistry in the lab (and unfortunately, I've completely evaded any formal training in chemistry). I have exposed some samples (I think details of the sample are ...
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3answers
122 views

Second order reaction with different reactants

In a laser photolysis reaction $\ce{C6H5NH2}$ $(C_0 = \pu{60 µM})$ is oxidized to its radical cation. The disappearance of the cation can follow three pathways: (1) Dimerzing of the cation, (2) ...
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2answers
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Semi-Infinite Potential Square Well: Negative Potential

I am having trouble with a problem involving a Semi-infinite potential square well: I have written down some notes that I added to the post. I have problems understanding the physical situation. See ...
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1answer
108 views

Calculating the biological standard potential

I have an electrochemical cell with following overall reaction: $$\ce{5 Sn^4+ + 2 Mn^2+ + 8 H2O <=> 5 Sn^2+ + 2 MnO4- + 16 H+}$$ I have defined the half reactions as: $$ \begin{align} \ce{Sn^...
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28 views

Why does ethanol have a stronger cooling effect on the body than water? [duplicate]

Why does ethanol have a stronger cooling effect than water (i.e. it feels cooler when dropped onto one’s hands) even though water has a higher heat of vaporization compared to ethanol? If we drop a ...
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1answer
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Relationship between auto-ignition temperature with pressure and fuel

Experimentally it appears that increase in pressure, fuel concentration, and chain length causes AIT to decrease until a minimum where even further increase in these parameters increases the AIT. ...
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56 views

What is heterogeneous catalysis in gas phase?

Give examples of heterogeneous catalysis (i) in gas phase and (ii) in liquid phase. Now, I came to know that heterogeneous catalysis involves different phases between the catalyst used and the ...
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Conception and manufacture of the Avogadro Project's (nearly) perfect silicon sphere (and, what is “atomic feeling”?)

The Avogadro Project, an effort prior to the recent redefinition of Avogadro's constant to design a nearly perfect sphere of silicon-28, apparently relied on the fine fingers of optician Achim ...
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1answer
143 views

How to color bonds by the strain?

I need to create a figure of a molecule in which the bonds are colored in a RGB scale according to the values read from a data file. The data file contains, for example, the increase or decrease in ...
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2answers
1k views

What is the “‡” symbol meaning in a reaction mechanism?

I was studying hydroboration from Clayden's Organic Chemistry [1, p. 1281] and the transition state had “‡” symbol in the upper right corner of the activated complex: We know that this is not the ...
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2answers
925 views

Find the pH of an amphiprotic salt dissolved in water at room temperature

Let's say I have a polyprotic acid $\ce{H2A}$ with the following properties: $$ \begin{align} \ce{H2A &<=> HA- + H+} & K_1 &= 1\cdot 10^{-1}\\ \ce{HA- &<=> A^2-+ H+} & ...
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2answers
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How can a catalyst not be included in a rate equation if, by definition, it speeds up a chemical reaction?

I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction. However, I have heard that catalysts can be involved in a reaction while not ...
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2answers
104 views

Prove Law of Chemical Equivalence [closed]

A somewhat infamous law (to me at least), that states: $$a.A_{eq}=b.B_{eq}=c.C_{eq}=d.D_{eq}$$ for any and every balanced chemical equation - $$a.A+b.B = c.C+d.D$$ where $i$ denotes the ...
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Why does like dissolve like?

Polar solvents love polar solutes to be dissolved in it and non polar with non polar. Often said as like dissolves like. Okay, polar loving polar can be understood with help of the facts: same polar ...
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1answer
744 views

What is the @ symbol used for in material science?

I came across the phrase "Silicone Rubber/Paraffin@Silicon Dioxide" also written as $\ce{SR/pa@SiO2}$, utilising the @ symbol. How can I understand what this means?...
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In a double displacement reaction, why don’t the two products reform after being dissolved in water? [duplicate]

Let’s say I have $\ce{AB (aq) + CD (aq) —> AD + CB}$. When AB and CD are dissolved in water, they get dissociated into their component ions. But why don’t they reform as AB and CD, if it is already ...
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Effect of pressure on transition temperature

I was wondering if someone can explain why the answer to the following question is volume instead of the others. If pressure has no effect on the transition temperature between two crystalline forms ...
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2answers
47 views

Shouldn't the pressure of gas above a liquid slightly decrease when some of its molecules dissolves in the liquid? [closed]

Lets say a liquid and gas above are in equilibrium. (1) Now if I suddenly increase the pressure of the gas it will take some time for some molecules of the gas to enter the liquid and get dissolved. ...
3
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1answer
247 views

Is the following rate law possible for the given reaction?

A researcher is investigating the following overall reaction: $$\ce{2C + D -> E}$$ The researcher claims the rate law for the reaction is written as follows: $\text{Rate} = k[\ce{C}][\ce{D}]$. Is ...
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1answer
40 views

What is the meaning of the J value in term symbols [closed]

I understand how to work out the J values of term symbols. e.g. a d1 configuration gives J values of 5/2 and 3/2. resulting in 2D 3/2 However I dont understand the meaning of it, and why it arises.
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700 views

Dependence of change in entropy on temperature

The thermodynamic definition of entropy is expressed as $$dS = \frac{dq_{rev}}{T}$$ I understand that it depends on amount of heat transferred because heat transfer can be understood as the degree of ...
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1answer
120 views

Nitrogen dioxide fluorescence quenching and lifetime

Nitrogen dioxide fluorescence quenching: $$ \begin{align} \ce{NO2 + h\nu &->[$\varphi_\mathrm{Ia}$] NO2^{\ast}}\tag{I}\\ \ce{NO2^{\ast} &->[$k_2$] NO2 + h\nu'}\tag{II}\\ \ce{NO2^{\ast} +...
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41 views

Reverse osmosis membrane used as an osmosis membrane

I recently came across the so-called 'thin-film composite membranes'. They are build up of layers with one of them being semipermeable. As I'm not well versed in chemistry, I'm unsure, if these ...
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1answer
48 views

3D printing of alumina

I want to print a structure of alumina, and the 3D printer that I am using is an extrusion-based printer. So I need your help in knowing that what composition (binders and deflocculant) of alumina ...
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3answers
130 views

How does the equilibrium shift when concentration of reactant and product are increased simulatenously

Before answering my question, take a look at this example $$\ce{2NOCl <=> 2NO + Cl2}$$ Let's suppose I have 2 mol/l $\ce{NOCl}$, 2 mol/l $\ce{NO}$, and 1 mol/l $\ce{Cl2}$ in a closed system. ...
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1answer
42 views

Water evaporation from calorimeter giving less exothermic enthalpy value?

To find the enthalpy change of combustion for an alcohol, you use a calorimeter filled with water and heat it by burning an alcohol. I was told that usually experimental values for the enthalpy ...
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1answer
46 views

Are phase transitions reversible when performed at supercooled temperatures?

For the state transition of supercooled water to ice, is the process reversible? I wonder this because I want to know if I can use entropy change of the universe is 0. If it isn't reversible, how do ...
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1answer
75 views

Find order of reaction 2A → B + C

Derive the integrated rate expression for a reaction of type: $$\ce{2A -> B + C}$$ I first need to determine the order of the reaction in order to find integrated rate law of that particular order....
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51 views

Why doesn't Delta S total = 0 for this reversible process?

My textbook (Engel Physical Chemistry 3rd Edition) says: For any irreversible process in an isolated system, there is a unique direction of spontaneous change: $\Delta S > 0$ for the spontaneous ...
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1answer
37 views

thinking about osmotic pressure when liquid is replaced by gas

An option in my test says: "The osmotic pressure of a dilute solution is the same as it would exert if it exists as a gas in the same volume of the solution and at same temperature." I'm not able ...
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1answer
186 views

Why are van der Waals' forces between gas molecules strong near its critical temperature?

My textbook says …easily liquefiable gases i.e. with higher critical temperatures are readily adsorbed as van der Waals' forces are stronger near the critical temperatures. What I do understand is ...
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2answers
88 views

How come we can't use the equivalence point equation of NV=NV in this problem?

So, the problem is you prepare to standardize a $\ce{Na2S2O3}$ solution. $\pu{32 mL}$ of $\ce{Na2S2O3}$ solution is titrated into $\pu{50 mL}$ of a $\pu{0.01 M} \ \ce{KIO3}$ solution to reach the ...

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