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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.

17
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2answers
908 views

Is it possible to speed up radioactive decay?

I’m aware that elements like $\ce{^14C}$ have a known half-life, which means that over a span of roughly $5730$ years, half of the $\ce{^14C}$ atoms decay into $\ce{^14N}$. Are there any substances ...
9
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1answer
2k views

The coldest (the most endothermic) reaction [closed]

What chemicals can you mix that causes the coldest (the most endothermic) reaction on a $\pu{kJ /kg}$ basis?
1
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0answers
67 views

What is the largest coupled cluster calculation that has ever been done (as of March 2019)? [on hold]

I am doing some research and trying to make sure the numbers I am reporting are accurate. I found that this paper says: "We were, however, able to complete a CCSDT(Q)/cc-pVTZ calculation on ...
2
votes
1answer
47 views

Determining the reduction potential of a half cell reaction at a given pH

$E^\circ_\ce{Cu^2+|Cu} = \pu{0.34 V}$. What will be reduction potential at $\mathrm{pH} = 14$ for the same couple? Given that $K_\mathrm{sp}$ of $\ce{Cu(OH)2}$ is $10^{-19}$. My Attempt I think ...
4
votes
1answer
113 views

How to determine the work function and electron velocities from data on the photoelectric effect?

A metal received light with wavelength $300~\mathrm{nm}$ in experiment A and light with wavelength $500~\mathrm{nm}$ in experiment B. In one experiment the electron speed was twice the speed of that ...
-2
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0answers
26 views

JEE Main Question - Find the Partial Pressure of Ammonia at equilibrium [on hold]

Consider the reaction, N2(g) + 3H2(g) ⇌ 2NH3(g) The equilibrium constant of the above reaction is Kp . If pure ammonia is left to dissociate, the partial pressure of ammonia at equilibrium is given ...
0
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0answers
16 views

CO2 IR extinction coefficients near the 15 micrometer band

I have searched multiple times for a spectrum or a table of the gaseous carbon dioxide Lambert-Beer extinction coefficients in the IR Earth thermal region. All I found was absorption spectra. Is ...
1
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0answers
16 views

Composition of gases in water using Henry’s law constants

The air is a mixture of a number of gases. The major components are oxygen and nitrogen with approximate proportion of $20\%$ is to $79\%$ by volume at $\pu{298 K}$. The water is in equilibrium with ...
4
votes
4answers
167 views

Why does the degree of dissociation change when we dilute a weak acid even though the equilibrium constant $K$ is constant?

$K$ represents the ratio of concentrations of molecules in a solution at equilibrium, which means that $Q_\mathrm{r}$ (that ratio at any given point) looks to be identical to $K$. In other words, the ...
0
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0answers
625 views

Calculating the energy released in cooling an ideal gas

Calculate the amount of energy released in cooling an ideal gas using the following information. Temperature change: 25 °C to 0 °C. Volume of container: 5 litres (remains constant). Pressure: ...
5
votes
1answer
109 views

Energy of photons of given frequency and number

I’m having trouble with calculating the energy of $\pu{5.00e10}$ photons of frequency $\pu{1.00e9 s-1}$. I know that to calculate the energy $E = hf$ is to be used. However, I am unaware as to what ...
0
votes
1answer
47 views

What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state?

When an electron in a higher energy state jumps to a lower energy state in Bohr’s model of hydrogen atom, it emits a photon which has energy equal to the difference in the energy between the final and ...
1
vote
1answer
19 views

Overall enthalpy balance on a mixing process

Let's say I have a mixing process involving $\ce{A}$ and $\ce{B}$ at temperatures $T_\ce{A}$ and $T_\ce{B}$, respectively. The $\ce{AB}$ mix is at temperature $T_p$. Our $ΔH_\mathrm{mix}$ is defined ...
-1
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1answer
6k views

Why does Le Chatelier's principle not apply to pure solids and liquids?

If we had a homogeneous reaction of pure liquids only, would Le Chatelier's principle still apply ? Also, wouldn't increasing the amount of solid in a heterogeneous reaction mixture at equillibrium ...
7
votes
2answers
76 views

Feasibility and Entropy

Suppose you've got some reaction that has a positive $\Delta H$, and also has positive $\Delta S_\mathrm{sys}$. Due to the equation $$\Delta S_\mathrm{tot} = \Delta S_\mathrm{sys} - \frac{\Delta H}{T}$...
6
votes
1answer
7k views

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 ...
4
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0answers
85 views

Approximate magnetic susceptibility of these liquid propellants?

This question asks if the comparatively large paramagnetic susceptibility of liquid oxygen (LOX) is considered when designing rocket tank and engine systems. This comment suggests fuels such as RP-1 (...
-2
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0answers
19 views

Can a fully ionized nucleus participate in any sort of chemical reaction [on hold]

If an element get fully ionized can it participate in any sort of chemical reaction?? Like H+ ion is also a bare nucleus and it react with other atoms normally. Can any other element's bare nucleus do ...
2
votes
1answer
27 views

Cobalt electroplating over nickel-plated steel

From my research, I understand that cobalt can be used on top of a nickel layer to improve durability of the nickel plating on a steel object. I am using a nickel anode and nickel acetate as ...
2
votes
1answer
63 views

How to calculate the volume or mass of carbon dioxide gas absorbed by a calcium hydroxide solution?

Carbon dioxide reacts with calcium hydroxide as shown by the equation: $$\ce{Ca(OH)2 (aq) + CO2 (g) -> CaCO3 (s) + H2O (l)}$$ A solution containing $\pu{0.1 mol}$ of calcium hydroxide reacts ...
0
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1answer
39 views

if a balloon full of warm air was placed in a refrigerator, what is the result? [on hold]

If a balloon full of warm air was placed in a refrigerator, What will happen to the Ballon ?
5
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2answers
381 views

What is a good source for large tables on the properties of water?

I'm currently doing an investigation for school on finding the Clausius-Clapeyron relation/gradient for boiling water and comparing it to the gradients along my line of best fit. It is given by the ...
10
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1answer
3k views

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 ...
13
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4answers
3k views

Why does liquid water form when we exhale on a mirror?

In the descriptions below, I always assume external pressure to be constant at 1 atm, the condition where daily observations are made. 1) When I exhale on a mirror, liquid water forms on the mirror. ...
1
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2answers
84 views

How to determine steady state of multi-step reaction with both reversible and irreversible steps?

I am trying to determine the relative concentrations of $\ce{U1}$, $\ce{U2}$, and $\ce{E}$ when the following reaction is at steady state. Note that $k_t$ is the zero order rate constant of new $\ce{...
3
votes
1answer
58 views

Minimizing energy of a molecule

I am minimizing energy of butane on the CHARMM Force Field and I am confused on how to go about getting a uniform unit for each different PE as in the potential energy for bond, angle, torsion, VDW, ...
-2
votes
0answers
20 views

Could someone help me with the chemistry question? [closed]

When black, solid copper (II) oxide is allowed to react with molecules of hydrogen gas, atoms of solid copper metal are formed alone with water. Symbolize the chemical changes by writing and balancing ...
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0answers
25 views

How to calculate the cell potential after the reaction has operated long enough for the Fe2+ to have changed by some concentration?

Consider the cell described below at $\pu{261 K}$: $$\ce{Fe | Fe^2+ (\pu{0.925 M}) || Cd^2+ (\pu{0.981 M}) | Cd}$$ Given $E^\circ_\ce{Cd^2+ -> Cd} = \pu{-0.403 V}$, $E^\circ_\ce{Fe^2+ -&...
-1
votes
1answer
26 views

Polyprotic Acid Titrations

Titrating a mixture of strong and weak acids will yield endpoints such that the volume of base required to reach each endpoint will be different for each acid, e.g. in a mixture of HCl and CH3COOH, ...
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0answers
56 views

Physical chemistry problem- thermodynamics [closed]

Calcium chloride is soluble in water according to the reaction: $$ \ce{CaCl2-> Ca^2+ + 2Cl-}$$ assuming that no heat transferred to the surroundings, calculate the change in temperature when 12....
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0answers
23 views

Determination of rate constant and activation energy [closed]

I was trying to determine the rate constant of saponification the reaction at two different temperatures by conductivity measurements.
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0answers
24 views

What are the steps to making a soluble salt? Please help i have a test tomorrow that's 80% of my grade! [closed]

Complete the method of preparing dry crystals of the soluble salt cobalt (II) chloride-6-water from the insoluble base cobalt (II) carbonate. The method involves 4 steps. Step 1: Add an excess of ...
0
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0answers
33 views

AP Chem Question about Reaction Rate - Confused?

I found this question in the AP Chem book, and I understand why B is the answer (as the answer key says). However, I don't understand why D is not also correct. The question is: A multistep reaction ...
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0answers
12 views

Would the presence of salt additives and impurities be of greater concern in measuring CMC by absorbance, fluorescence or conductivity?? [closed]

In measuring critical micelle concentration using absorbance fluorescence or conductivity, which one is most affected by the presence of salt additives? Why is that?
2
votes
1answer
37 views

How do salt additives and impurities affect a critical micelle concentration?

So I understand that a CMC typically decreases as more salt additives are added. What I am not clear on is how exactly. The head groups are charged in this example (one anionic and one cationic) so ...
9
votes
1answer
2k views

Plotting a Langmuir adsorption isotherm

We have, $$\theta = \frac{Kp_\mathrm a}{1+Kp_\mathrm a}$$ where, the fractional coverage $\theta$ is defined as the number of sites occupied by adsorbate $A$ over the total number of sites. $p_\...
0
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2answers
64 views

Why is the rate of reaction calculated as d[A]/dt?

For example, for a simple chemical reaction like $$\ce{A -> C}$$ the rate of the reaction could be calculated as the rate of appearance of $\ce{C}$ or the disappearance of $\ce{A}$, which makes ...
0
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2answers
94 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 ...
8
votes
2answers
205 views

Calculating the strength of an ionic bond that contains poly-atomic ions

So the bond association enthalpy for ionic compounds like $\ce{NaCl}$ and $\ce{NaBr}$ can be easily calculated from a Born-Haber cycle. But the way a Born-Haber cycle is constructed it uses info that ...
1
vote
1answer
31 views

Why do reactions happen at all? [closed]

What makes some atoms/compounds reactive and some noble? What is the fundamental truth behind a reaction? It seems that two species can undergo number of combination to give a compound. Say Sodium and ...
3
votes
1answer
4k views

Can dissolution reactions be endothermic?

Is it possible for a dissolution reaction of the form $$\ce{X(s) ->[solvent] X (solv)}$$ or $$\ce{M_mX_x (s) ->[solvent] m M^x+ (solv) + x X^m- (solv)}$$ to be endothermic, i.e. $\Delta_\...
5
votes
2answers
105 views

Lagrange Multipliers for the derivation of Maxwell-Boltzmann distribution

When deriving the MB-Distribution while taking the number of quantum states $g_j$ into account, the final equation I'd have to solve would be: $$\ln(g_j)-\ln(n_j)+\alpha+\beta\cdot E_j=0$$ Where $n_j$ ...
2
votes
0answers
22 views

Shortcut method to find atomic term symbols ignoring the spin orbit coupling

Is there any shortcut method by which we can find the atomic term symbols ignoring the spin-orbit coupling, i.e. ignoring the values of J. For instance, when writing the d-d transitions for any ...
5
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0answers
53 views

Helmholtz double layer

I don't quite understand what is meant by the Helmholtz double layer. Textbooks states something along the lines of: the colloidal particles attain charge by selective adsorption, due to this it ...
0
votes
1answer
39 views

Why does the colour of gold sol change with particle size? [duplicate]

Regarding the colour of gold sol, my book says Finest gold sol is red in colour; as the size of particles increases, it appears purple, then blue and finally golden. This is the image I found on ...
0
votes
1answer
33 views

Determination of pKb of a mono acidic base

$20$ mL of a weak monoacidic base($\text{BOH}$) requires $12$ mL of $0.3$ M $\text{HCl}$ solution for the equivalence point. During titration, the pH of the base solution was $10$ upon the addition of ...
0
votes
1answer
48 views

What are the effects of salt additives and impurities on the CMC? [closed]

I understand what a critical micelle concentration (CMC) is, however I do not know why or how impurities or salt additives affect it when measured in specific ways. Any help is much appreciated. So ...
1
vote
1answer
18 views

Relation between electron gain enthalpy and electron affinity

The correct relation between electron gain enthalpy $(Δ_\mathrm{eg}H)$ and electron affinity $A_\mathrm{e}$ at any temperature '$T$' is A) $Δ_\mathrm{eg}H = -A_\mathrm{e} - \frac{5}{2}RT$ B) ...
4
votes
2answers
1k views

What will happen to the entropy and free energy of the gasses when the partition is removed?

Consider a container of volume $ 5.0$ L that is divided into two compartments of equal size. In the left compartment there is nitrogen at $1.0$ $atm$ and $25 °C$; in the right compartment ...
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votes
1answer
28 views

What is the velocity of de Broglie wave?

Here is my calculation: note: $ν$ – frequency, $V$ – velocity of wave, $v'$– velocity of object. $$ \begin{align} λ &= h/mv' \tag{1}\\ mc^2/h &= ν \tag{2}\\ λν &= V \quad \text{(wave ...