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.
3,133
questions
2
votes
1answer
405 views
Identifying the gas given ratio of its specific heats
The ratio of the heat capacities $\frac{C_\mathrm p}{C_\mathrm v}$ for one mole of a gas is $1.67$. The gas is:
a) $\ce{He}$
b) $\ce{H2}$
c) $\ce{CO2}$
d) $\ce{CH4}$
I know how to answer ...
1
vote
1answer
264 views
Storing kinetic energy in bonds
Let's assume a setup with a static linear molecule with three identical atoms connected by bonds and a single atom, identical to the other three, being shot at the molecule. Let's also assume that ...
4
votes
1answer
6k views
Finding electron configuration of lanthanide ions
When I have a gadolinium ion ($\ce{Gd^3+}$), how can I calculate its electron configuration?
$$\ce{Gd} : \mathrm{[Xe] (4f)^7 (5d)^1 (6s)^2}$$
Do I need to first subtract the 2 electrons in the $\...
12
votes
2answers
24k views
Difference between Reaction Rate and Rate Law?
Lets say you have the reaction
$$\ce{$a$A + $b$B -> $c$C + $d$D}$$
The rate of the reaction is given by the change in initial concentration over the change in time.
$$-\frac{\Delta \left[\ce A \...
0
votes
2answers
100 views
Balancing Oxidation-Reduction equations
Anode: $\ce{2 H2O_{(l)} -> O2 + 4 H+_{(aq)} + 4e^-}$
Cathode: $\ce{ 2 H2O_{(l)} + 2 e- -> H2_{(g)} + 2 OH-_{(aq)}}$
Can someone show me the steps for adding the two. For the overall reaction,...
3
votes
0answers
387 views
How will the transference number of H+ ion in a dilute solution vary as temperature increases?
I know that transference number depends on Ionic mobility, which depends on temperature. But is there any equation which describes the relation of Transference number and temperature, any ions like H+....
7
votes
1answer
4k views
What is the colloidal osmotic pressure?
The oncotic pressure or colloidal osmotic pressure is the osmotic pressure developed due to the presence of colloids in a solution. But since the colloids are not true solution, why should the ...
8
votes
3answers
8k views
Activity of hydrogen ion
I am not from chemistry background. Could you tell me in simple words what the activity of hydrogen $a_{\ce{H+}}$ is? It arises in the context that the negative logarithm of the activity of hydrogen ...
45
votes
4answers
3k views
Unit of the equilibrium constant: contradiction of Bridgman's theorem?
The following equation is standard in thermodynamics:
$$
\Delta G^\circ=-RT\log(K)
$$
where $K$ is the equilibrium constant. In dimensional analysis, Bridgman's theorem tells us that the argument ...
1
vote
1answer
11k views
Finding molar mass of an unknown acid
"In the titration of a solid acid, an endpoint is reached after 22.0mL
of 0.120 M $\ce{NaOH}$ has been added. Assuming that each acid particle
contains two acidic hydrogens and both are ...
14
votes
1answer
2k views
Why is the carbon dioxide we exhale transparent?
Why is carbon dioxide that comes from dry ice opaque and smoky while the carbon dioxide that we exhale transparent?
0
votes
1answer
222 views
Oxidation number and Pourbaix diagrams
In a Pourbaix diagram (E-pH diagram) where the regions are given , but the assignment of these to the elements we have is not done yet , how can the oxidation numbers helps me out assigning each ...
8
votes
1answer
396 views
Consequences of using reagent preserved with sodium azide on gold film
I am running experiments using reagents preserved with 0.1% sodium azide, which are applied to a gold film. Unfortunately, there are very few options for using reagents without sodium azide.
I ...
3
votes
1answer
369 views
Would concentration of a compound in equilibrium increase even if it's not favored by a volume decrease?
So say I have a reaction where there are x moles of gas on the reactant side, and y moles of gas on the product side, where x>y. The volume decreases, favoring the products side. The textbook I am ...
5
votes
1answer
16k views
Determine concentration Using Beer's law
How do you determine concentration of a sample using wavelength and absorbency? Say our wavelength for a sample of Red 40 is 508.50 nm and absorbance is 0.283 when we use 6ml water and 4 ml Red 40. ...
0
votes
2answers
692 views
How would I write an input Lammps command for continuous change in temperature? [closed]
I'm going to study the thermal expansion of graphite. For this goal, I should change the temperature continuously. But I do not know how to code it by Lammps?
2
votes
1answer
3k views
Why doesn't diffusion take place between immiscible liquids?
If we take a test-tube of bromine and invert an upside-down test tube of air on top of it, it'll diffuse with the air, until the bromine is thoroughly 'mixed' with the air in both test tubes. But why ...
6
votes
2answers
11k views
Azeotropes and separation by distillation?
I have just recently learnt the theory of fractional and normal distillations and the basics of maximum and minimum boiling azeotropes.
Most books say that the components of the mixture forming an ...
-7
votes
1answer
15k views
Equivalent weight of metal [closed]
A metal oxide contains $60$% metal.The equivalent weight of metal is
(1) $12$
(2) $60$
(3) $40$
(4) $24$
I know that the equivalent weight of metal oxide = equivalent weight of metal + 8.But how ...
2
votes
1answer
80 views
Reaction with carbon
Usually maximum time we see then after cooking by gas there is no black spot on the pot. But continually burning can affect the pot surface and makes black powder.
My question is:
What is the ...
3
votes
2answers
818 views
Bond of interest
What does it mean for our bond of interest if we have low bond length and high frequency? Trying to make this connection but am not understanding. If anyone could explain it intuitively, that would be ...
2
votes
1answer
170 views
What does this scale mean?
$$\log_{10}~\mathrm{pg}/\mathrm{ml}$$
I do not understand the scale. How do I convert this to a standard concentration (without the logs)?
3
votes
1answer
2k views
Why are partial molar Gibbs energy and Gibbs energy per mol equal?
I'm not a chemist, but I need some insight into chemical thermodynamics.
In the book that I'm reading (Nevers, 2012), equation (4.28) relates the chemical potential of a pure species to it's Gibbs ...
4
votes
2answers
474 views
Gold nanoparticles in a water/oil environment
I am currently investigating the assembly of gold nanoparticles in a mixture of water and oil. The thing is the following: If we have gold nanoparticles (35nm diameter) dispersed in water and we put ...
5
votes
2answers
2k views
How to determine a Reynolds number for mixture of 2 liquids
I'm experimenting with synthesis in microreactors and I'm using 2 reactants. I'd like to estimate the Reynolds number of the flow containing two miscible fluids. I have the values of their properties (...
3
votes
2answers
196 views
Is this relation in case of a mixture of ideal gases valid?
I came across the following relation in a book (written as a fact, with no proof), for a mixture of ideal gases both at the same pressure and temperature. The final volume of the mixture of gases ...
4
votes
2answers
4k views
Wave function for particle in a infinite well located at -L and +L
The wave function for a particle in a infinite potential well located at $0$ and $L$ is $$\psi_n=\sqrt{\frac2L}\sin\frac{n\pi x}L$$
I want to find our wave function for the same situation where the ...
4
votes
1answer
142 views
Soil-solution cations in competition for exchange sites
How could one determine the likelihood of one cation displacing another on a negatively charged exchange site of a clay particle?
For example, in a soil solution containing equal parts (by number of ...
5
votes
1answer
1k views
Ca and Mg hydrated radius in clay flocculation
Ca has an atomic radius of $197\mathrm{~pm}$ and a Pauling electronegativity of $1.00$.
Mg has an atomic radius of $197\mathrm{~pm}$ and a Pauling electronegativity of $1.31$.
Since Mg is smaller ...
5
votes
2answers
112 views
Cement strength by moistening
After cementing a wall, water is applied on the surface to keep it moist to maintain its strength for the next few days. Why is this necessary for maintaining the strength of the concrete?
29
votes
2answers
25k views
What exactly is hydrogen bonding (and does it really need fluorine, oxygen, or nitrogen)?
I'm not satisfied with the rationale for the intermolecular attraction known as hydrogen bonding. In my book, it states that
Hydrogen bonding is a special type of intermolecular attraction between ...
8
votes
1answer
13k views
How do equilibrium shifts affect solids?
Say we have the following reversible reaction: $$\ce{NaOH{(s) }<=> Na^+{(aq) }$+ $OH^{-}{(aq)}} +10.6 \mathrm{kcal}$$
If we add $\ce{OH^-}$ and equilibrium shifts to the left, does that affect ...
4
votes
1answer
948 views
Effect of vibration on wine quality
Most people that have ever visited a viticulteur (winemaker) will know that it is common wisdom that vibrations are bad for the wine quality. When I was just a kid the winemaker always told me that we ...
44
votes
3answers
306k views
Why is it important to use a salt bridge in a voltaic cell? Can a wire be used?
I was learning about voltaic cells and came across salt bridges. If the purpose of the salt bridge is only to move electrons from an electrolyte solution to the other, then why can I not use a wire?
...
9
votes
2answers
6k views
How to determine the empirical formula for an unknown iron oxide?
I have to determine the empirical formula of an oxide of iron which has $69.9\%$ iron and $30.1\%$ dioxygen by mass in it.
I have started as follows:
For our convenience we take $\pu{100 g}$ of that ...
5
votes
1answer
11k views
What is the effect of adding salt to ice?
What will happen to the melting point temperature of ice if some common salt is added to it? How to justfy the answer?
22
votes
1answer
434 views
Molecular Imaging - Any surprises to be had?
Molecular imaging, using STM and AFM technologies, appear so far to visually prove most of what we already know about chemical structures, such as VSEPR theory. For instance, here are the ideal ...
4
votes
2answers
1k views
Chemical Equilibrium - Why does changing the temperature shift the equilibrium?
I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side.
I know that $\Delta G = \Delta H − T\Delta S $ but I don't know how to ...
6
votes
3answers
3k views
How can I measure the pH of high-viscosity fluids like dough?
I would like to measure the pH value of dough with a pH-Meter, to ensure a pH value of 4.1 (max). Because of the high viscosity I would thin down the dough with demineralized water for two reasons:
I ...
1
vote
0answers
34 views
Chemical Equilibrium - Why does changing the temperature shift the equilibrium? [duplicate]
I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side.
I know that $\Delta G = \Delta H - T \Delta S$ but I don't know how to ...
5
votes
3answers
3k views
Why do you need a strong base for a titration
For a titration, if you want to know the concentration of an acid you use a strong base such as $\ce{NaOH}$. My question is; why you can't use a weak base for this purpose? Is it because the ...
7
votes
1answer
161 views
Interpretation of Figure - biofunctionalization
In this paper on page 1985 they say:
Fluorescence analysis confirmed that enhanced protein binding at higher electron dose depends only to a small extent on the slight increase in the lateral ...
0
votes
2answers
5k views
How does the volume of a mole of ideal gas relate to pressure and temperature?
The volume of a mole of gas is:
$\ce{22.4 l}$
directly proportional to pressure and Kelvin temperature.
directly proportional to pressure, inversely proportional to Kelvin temperature.
inversely ...
2
votes
2answers
6k views
How many valence electrons does the azide ion have?
We had a test and and we had a question asking the number of valence electrons in an azide ion, $\ce{N3^{-}}$. I find out that the answer is 16 but I could not understand how.
I saw the structure. ...
11
votes
3answers
8k views
Can you heat water with additives?
I have been curious about this question for a while. If you want to warm up a large amount of water, is it feasible to do this by adding a substance that has an exothermic reaction with the water? ...
2
votes
2answers
195 views
Helium empirical wavefunctions
I know that analytic forms of the Helium wavefunctions are not known. However, are there empirical expressions for the low-lying states of Helium? I'd like to use them to calculate some transition ...
5
votes
2answers
3k views
Finding Pv in Pv=nRT for molecular hydrogen
I'm attempting to write a small program that will calculate the values for the Ideal Gas Law, specifically for molecular Hydrogen (H2) in space. Eventually, this will grow to be a sort of "simulator",...
10
votes
4answers
5k views
Chemical properties of isotopes
I've always heard that different isotopes of the same element have exactly the same chemical properties.
But for example, I've read that some compounds which have hydrogen atoms interchanged by ...
1
vote
3answers
2k views
On the scale of stuff with a pH
I am a confused (and somewhat anal retentive) non-chemist who is trying to understand what pH is. I have come to understand it is a measure of acidity, but I have not yet figured out what that means ...
9
votes
4answers
82k views
Why calcium chloride is used to melt ice over sodium chloride
I'm not quite sure I understand this. My question is:
Calcium chloride is a salt used widely to melt ice on sidewalks and roads. Explain why one mole of $\ce{CaCl2}$ would be more effective than ...
