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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15
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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 ...
2
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2answers
848 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+} & ...
7
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2answers
6k views

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 ...
3
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2answers
103 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 ...
13
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2answers
12k views

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 ...
7
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1answer
742 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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2answers
38 views

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 ...
0
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1answer
23 views

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 ...
1
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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
votes
1answer
245 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 ...
2
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1answer
39 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.
7
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5answers
676 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 ...
5
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1answer
118 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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0answers
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 ...
2
votes
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 ...
2
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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. ...
1
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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 ...
1
vote
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 ...
-1
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1answer
74 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....
0
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0answers
48 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 ...
0
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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 ...
6
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1answer
168 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
83 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 ...
4
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0answers
58 views

Symmetry Adapted molecular orbitals of Formaldehyde

I am currently trying to find the Symmetry Adapted linear Combinations (SALCs) of Formaldehyde $\ce{H2C=O}$, and use the 1s orbitals on the hydrogen atoms, and 2s, 2px, 2py and 2pz orbitals on the ...
1
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1answer
105 views

Fundamentals of mathematics and physics for physical chemistry [closed]

Before I start studying chemistry, I want to gain some knowledge about the fundamentals of mathematics and physics that are important to better understand the principles of physical chemistry, ...
7
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1answer
80 views

Product operator analysis for CHn groups in HSQC and HMQC

I'm taking and advanced NMR course this semester and we are learning about product operator formalism. I have a homework where I'm supposed to apply this formalism to an HSQC and HMQC experiment. The ...
2
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0answers
46 views

What is the precise meaning of “in-phase” (and “out-of-phase”) in this context?

I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled Symmetry: Infrared and Raman Active Vibrations, the author says the following: ...
0
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1answer
45 views

Rate law of reactions, what about the proportions? [closed]

Consider the reaction $$\ce{A + B + C -> D + E}$$ and $\mathrm{rate} = k[\ce{A}][\ce{B}]^2.$ My book said if we double the amount of $\ce{A},$ then the reaction rate will double. I understand ...
2
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2answers
2k views

The respective speed of five molecules are 2, 1.5, 1.6, 1.6 and 1.2 km/s. The most probable speed in km/s will be?

The respective speed of five molecules are 2, 1.5, 1.6, 1.6 and 1.2 km/s. The most probable speed in km/s will be? 1. 2 2. 1.58 3. 1.6 4. 1.31 I think the answer should be 1.6 km/h but the ...
1
vote
1answer
31 views

Raman scattering and “electron and proton center” of molecule

I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled The Raman Scattering Process, the author says the following: Light scattering ...
2
votes
2answers
514 views

Given this liquid-liquid phase diagram, is the green line the nitrobenzene-rich phase?

The temperature-composition diagram for hexane and nitrobenzene at 1atm. The region below the curve corresponds to the compositions and temperatures at which the liquids form two phases. The upper ...
1
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1answer
34 views

Contradiction in variation of conductance and conductivity on dilution

I do conceptually understand that on dilution conductivity decreases and conductance increases but if we look at the formula of conductivity, a contradiction seems to arise. $$\kappa=GG^*$$ where $\...
3
votes
2answers
243 views

What is the correct pH value of weak and strong alkalis? [closed]

In the book titled fundamental chemistry for Cambridge O level, it states at page 149, Ammonia solution with a pH of 11.1 is a weak alkali and that's why it shows much lower conductivity of 0.50 ...
0
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1answer
44 views

Entropy change of surroundings and system

The entropy change of the surroundings can be calculated by the equation $dS_{sur}=\frac{dq}{T_{sur}}$ regardless of the path (irreversible or reversible). The argument is that because the ...
1
vote
1answer
158 views

Maximum number of atoms in the ground state

I was given the following question. A sample contains $100$ identical and hypothetical $H$-like atoms ( $Z$ may be fractional). Out of the given atoms, some are in the ground state, while others are ...
7
votes
1answer
646 views

Boiling point of oxygen

I am studying chemistry from the book titled "Fundamental Chemistry for Cambridge O Level" written by Rosemarie Gallagher and Paul Ingram. On page 17, it states that oxygen boils at −219 °C and ...
1
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0answers
45 views

Calculating Gibbs free energy for the reaction of burning methanol

Calculate $Δ_\mathrm{r}G^\circ$ for the following reaction: $$\ce{2 CH3OH(l) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)}$$ using $Δ_\mathrm{r}H^\circ$ and $Δ_\mathrm{r}S^\circ$ at $\pu{298.13 K}$ $(\pu{25 °C}...
0
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2answers
52 views

Calculating ratio of conjugate base and acid when pH and pKa are given

Buffer solutions are used by biological mammalian systems to maintain the $\mathrm{pH}$ of blood plasma within a narrow range. In these systems, the compound from which this solution is obtained is $\...
2
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0answers
48 views

Can a catalyst appear in the rate equation? [duplicate]

According to Wikipedia: Chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway with a lower activation energy than the non-...
0
votes
1answer
49 views

Why are pressure or volume not able to change the equilibrium constant? [duplicate]

It is stated in my textbook that temperature is the only factor that can change the equilibrium constant. According to the Ideal Gas Law, temperature is dependent on the pressure and volume. Thus, ...
-1
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2answers
119 views

The amount of heat energy required to raise the temperature of 1g of helium at NTP from T1 K to T2 K is?

The amount of heat energy required to raise the temperature of 1g of helium at NTP from $T_1 \pu{K}$ to $T_2 \pu{K}$ is? My confusion is, that as the gas is at NTP, therefore, it is an isochoric ...
-1
votes
1answer
44 views

How to find the number of valence electrons with the help pf quantum numbers? [closed]

I'm bit confused on how to find the number of valence electrons. For example, Boron ($\ce{B) has the electronic configuration as: $\mathrm{1s^2 2s^2 2p^1}$. So what would be its number of valence ...
1
vote
1answer
117 views

How is Raoult's law a special case of Henry's law and not vice versa?

I know that Raoult's law can be a special case of Henry's law when the value of the Henry's constant becomes equal to the vapour pressure of the pure state of the liquid. Why can't we say the opposite,...
-2
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1answer
75 views

Why do azeotropes boil at constant temperature? [closed]

As given in the Wikipedia page, An azeotrope (/əˈziːəˌtroʊp/) or a constant boiling point mixture is a mixture of two or more liquids whose proportions cannot be altered or changed by simple ...
7
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2answers
153 views

Open resource for spectroscopic raw data

Is anyone aware of reliable resources (ideally public) which allow the user to download the raw spectroscopic data such as infrared spectrum of small organic molecules, or rotational spectrum of HCl/...
9
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1answer
2k views

Does the van der Waals equation remain valid when repulsive intermolecular forces dominate?

The van der Waals equation for a real gas is: $$RT =\left(p+\frac{a}{V_\mathrm{m}^2}\right)(V_\mathrm{m}-b)$$ We have understood this formula by saying that $a$ is the term which is for force of ...
5
votes
1answer
23k views

Calculating Compressibility factor from the Van der Waals' Gas equation

So this problem has been bugging me for a long time. According to Wikipedia the compressibility factor $Z$ is defined as the ratio of the volume occupied by a real gas divided by the volume occupied ...
4
votes
1answer
4k views

How are van der Waals parameters determined experimentally?

If the ideal gas law $PV=nRT$ is not enough, as a second approximation the van der Waals equation $$\left(P+a\frac{n^2}{V}\right)\left(V-nb\right)=nRT$$ is applied. The constants $a$ and $b$ are van ...
1
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1answer
1k views

Validity of van der Waals equation [duplicate]

Van der Waals had stated that at high pressure, pressure exerted by ideal gas on the walls of container is more than real gas. However in this graph, one can clearly see that, the at high pressure ...
10
votes
1answer
2k views

Calculation of Atomic weight percentage in AAS

I am currently doing doping studies in a system similar to this ($\ce{A_{x}B_{1-x}}$) and I have to find atomic weight percentage of $\ce{B}$ element using atomic absorption spectroscopy(AAS). I have ...

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