Tagged Questions

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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Why is active mass of a pure solid or liquid always taken as unity?

Active mass is defined as the molar concentration ie. number of Gram-moles per litre. My book then wrote Active mass of pure solid/liquid is always 1 . The book reasoned that Molar ...
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1answer
46 views

Net charge of Peptides at pH1 and pH0

Taking Glycine and aspartic acid. As both the amino acids are fully protonated at pH 0 ad pH 1, how does the peptide bond form? Is it a two step mechanism where the OH from an alpha carboxyl group ...
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1answer
22 views

Acid-Base Titration: Do Acids and Bases Have the Same Coefficients of Moles if They Neutralize One Another?

The questions states: Ammonia has the formula NH3. Household ammonia is a dilute aqueous solution of NH3. Aqueous ammonia is a base that can neutralize acids. If 18.2mL of 0.800 M HCl solution are ...
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31 views

Application of Grahms Law of diffusion

$\ce{H2}$ (di-hydrogen) and $\ce{He}$ are kept in a container at partial pressure $p_1$ and $p_2$. A thin perforation is made in the wall of the container and it is observed that both gases diffused ...
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1answer
30 views

Is there a heat capacity of an object when it is melting?

Is there a heat capacity of an object when it is melting? I'm questioning it since the temperature doesn't change during phase transitions and the units of heat capacity is Joules/Kelvin.
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35 views

Why is the Standard enthalpy of formation of O2 and other reference forms of element zero?

Well, from what I know bonding releases energy. And does anybody know a source for finding the reference form of element at standard conditions?
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1answer
32 views

How are cathode rays produced?

Why cathode rays are produced if pressure of the gas discharge tube is lowered to about $10^{-4}$ atm? How bombardment of glass of gas discharge tube from cathode ray result in a faint glow?
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1answer
35 views

Does Combining Solid/Liquid Concentration with $K_c$ Matter when Comparing $K_c$ of Different Reactions?

I know it is convention to take liquid/solid concentrations as constants and lump it with the equilibrium constant. However, if we were trying to compare the equilibrium constants of two different ...
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How do I calculate the molar mass of an unknown gas?

A piston is placed in a closed tube. To the left, there is Hydrogen Gas at 400K and 4 atm. To the right, there is an unknown gas at 200K and 2 atm. At equilibrium, the piston is at 1/3 of the length ...
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2answers
37 views

Grams to volume question?

How many liters of $\ce{H2(g)}$ at STP are produced per gram of $\ce{Al(s)}$ consumed in the following reaction? $$\ce{2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)}$$ Express your answer to four ...
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34 views

What is the pressure (in atmospheres) of the gas inside a container connected to an open-end, mercury-filled manometer? [closed]

What is the pressure (in atmospheres) of the gas inside a container connected to an open-end, mercury-filled manometer? The atmospheric pressure is 0.95 atm. My answer was 0.24 How was 1.19 atm the ...
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49 views

Molecular bond angles

How do Bond angles vary in molecule with a lone pair and central atom of different electronegativity, but in the same period so that ecectronegativity matters more than orbital size? Assuming that the ...
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1answer
21 views

Confusion with Law of Equivalence

Law of Equivalence states that One equivalent of an element combines with one equivalent of the other. Equivalent of $\ce{Na}$ is $22.99$ & that of $\ce{0}$ is $8$. By the Law of ...
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1answer
35 views

Bond Dissociation Temperatures for Hydrocarbons

I'd like to know the temperatures that various hydrocarbons such as methane, butane, and propane, etc. will dissociate into hydrogen and carbon. Is there a reference where I can look up these ...
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1answer
40 views

Element letters

Does it change the compound if the element letters are switched? ex. HO or OH. Are those two different compounds or are they one in the same? This may be a simple question or I may have incorrectly ...
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1answer
61 views

What is the entropy of mixing of two ideal gases starting out with different pressures?

The entropy of mixing of ideal gas is given by this equation: $\Delta S_{mix} = -nR(x_1\ln x_1 + x_2\ln x_2)$ Does this equation works only when the initial conditions of both compartments are at ...
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27 views

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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1answer
82 views

Additional Questions Regarding Free Energy Requirements for Reacting Gases

Continued from my previous question here. With regards to the Boltzmann factor, I am confused on what type of terms we can substitute for E. I know kinetic energy is one, free energy as well, but ...
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1answer
167 views

Why do we use dG < 0 to describe a spontaneous process?

With something like a reaction or phase change, all sources use the criterion that $dG < 0$ for the reaction to be spontaneous and then substitute an appropriate expression for $dG$ to the specific ...
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1answer
35 views

Orbital angular momentum

For hydrogen atom, L^2 and Lz can be obtained as eigenvalues for a particular wave function. But that does not completely specify the angular momentum vector. How to get about this problem? Also, in ...
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1answer
68 views

Confusion about the relationship between free energy and kinetic energy for reacting gases

I am confused about the energies we are talking about when speaking in regards to the Maxwell Boltzmann Distribution and activation energies. Is there an relationship between kinetic energy and ...
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0answers
24 views

Additional Questions Regarding the Auto-Ignition Temperature

I had some followup questions regarding a previous post I made here regarding the auto-ignition temperature and ASTM E659 For fuel temperature below AIT, we should still have finite reactants above ...
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1answer
69 views

Mechanics Behind the Auto Ignition Temperature

I have some questions about the auto-ignition temperature for fuels. Per ASTM E659: AIT (auto-ignition temperature) is the lowest temperature at which the substance will produce hot-flame ignition ...
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34 views

Equilibrium constant and reaction Quotient

does reaction quotient After equilibrium has been achieved make any sense? At equilibrium point rates of forward and backward reaction are same and the system is in dynamic equilibrium.The graph of ...
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0answers
52 views

Finding Root-Mean-Square of Ne using kinetic energy?

I am not being able to solve the following question: -Find the root-mean-square speed of $\ce{Ne}$ atoms at the temperature at which their kinetic energy is $\mathrm{6.24\ kJ/mol}$. I tried ...
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1answer
56 views

How can a catalyst not be included in a rate equation, if it by definition 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? But I have heard that catalysts can be involved in a reaction while not being ...
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2answers
63 views

What is the best way to explain why aluminum has a lower first ionization energy than magnesium?

I used to use the explanation that s orbitals penetrate better than p orbitals. However, could the explanation be that 3s is shielding the 3p in aluminum?
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1answer
94 views

Proof that Equilibrium Constant is a Ratio of Rate Constants

I have a question about this proof that shows the relationship between the rate constant and the equilibrium constant. In this proof, the assumption is that the reaction is (a+b)th order (forward) and ...
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1answer
50 views

Proof of kinetic energy equation

Is there a way to prove that $\frac{1}{2} mv^2 $$= \frac{3}{2}RT$ The first one is kinetic energy and the second is the average kinetic energy. Can this be proved by component of velocity.
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50 views

Relationship between Equivalence Ratio and Adiabatic Flame Temperature for Fuel Rich Combustion

I'm reading a combustion text and would like help interpreting the following passage (diagram attached). It is regarding the relationship between equivalence ratio and adiabatic flame temperature: ...
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1answer
63 views

A few basic questions about activation energy and the Maxwell-Boltzmann distribution

I understand activation energy to be the relative difference in energy between that of the activated complex/transition state (at some temperature) and the average energy of the reactants like shown ...
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2answers
62 views

Nernst equation and electrolysis

Let's say we have a stable solution of $\mathrm{A}_{\left(\mathrm{aq}\right)}^{2+}$ and $\mathrm{C}_{\left(\mathrm{aq}\right)}^{+}$ , with their respective counter-ions. The associated redox ...
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1answer
32 views

Can the electron configuration of Te be written that way?

Normally, the electron configuration of Te is known as: $$\begin{aligned} {[Kr]} 5s^2 \ce{4d^10} 5p^4 \end{aligned}$$ Then, one day I was asked in a exam if this can be written also as: ...
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Is my analysis correct when answering this question about quantum numbers?

Which series of quantum numbers describes the highest (energy) occupied orbital in a ground state of At atom? a) n = 6, l = 0 b) n = 6, l = 2 c) n = 5, l = 2 d) n = 4, l = 3 e) n = 6, l = 1 ...
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1answer
161 views

A thermos bottle containing milk is shaken vigorously

I have a conceptual physical chemistry question here. A thermos bottle containing milk is shaken vigorously. Consider the milk as the system. Will the temperature rise as a result of the shaking? ...
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2answers
90 views

Electron shells

Can we compare the electron shells with the orbits of the planets around the Sun, is this a good comparison? Is it true for all the atoms that they can have only 2 electrons on the first shell, but ...
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1answer
86 views

Does everything exist as a gas at P = 0?

Attached is a phase diagram for carbon dioxide. At P = 0, it appears that the substance will exist as a gas regardless of temperature. My questions are: For any liquid at a fixed temperature, is ...
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1answer
86 views

Do reverse reactions occur in combustion?

I am currently reading a textbook on combustion. They assume that all reactions go to completion, such that post combustion only unburned fuel/air and actual products remain. Assuming that combustion ...
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1answer
42 views

How can I compute molar concentration if I am given parts per trillion?

A question in my book asks... You have a gas X that is found in quantities of $261~\mathrm{PPTV}$ (parts per trillion by volume). Compute the molar concentration at $283.15~\mathrm{K}$ and ...
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1answer
67 views

Does someone know the name of this equipment?

I think it is used to measure force or something like that. I broke it and have to buy a new one.
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0answers
31 views

How to begin solving this wave function for linear momentum in the x-direction [closed]

I just need help at least starting this problem, especially applying Euler's Formula to it. So far, I thought about converting this into $Ae^{(ikx)}$ format, but I was confused on why it was asking ...
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1answer
46 views

Explicit differential equation based model of protein folding

I am an applied mathematician interested in the dynamics of potential systems - i.e., systems with multiple unique energy minima. One of the best examples of such systems are protein folding ...
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4answers
918 views

How many unique molecules exist? And how many exist only by synthesis?

I'm interested in How many unique molecules (of all types: organic and inorganic, etc), exist in the world accessible by man (let's exclude black holes and the centers of stars etc)? What subset ...
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1answer
65 views

Prevent molten glass from cracking when cooling down

My mother works in a ceramics workshop. Besides giving lessons she creates various ceramic dishes, cups and plates. She often uses the effect of colored glass melting in the product and then leaving ...
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1answer
37 views

Reversible elementary reaction

I have a question regarding a reversible elementary reaction: If we have an equilibrium where $$\ce{A<=>[k_1][k_{-1}]B}$$ , then $$-d[A]/dt= k_1[A]-k_{-1}[B]$$. If we take $$[B]=[B]_0 + ([A]_0 ...
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0answers
23 views

Significance of Kinetic Velocities?

In the concept of Kinetic Molecular Theory we have rms(root mean square), avg(average) and mp(most probable) velocities. I understand the concept well. But my question is why do we have three ...
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1answer
39 views

Molecularity vs Order Of Reaction

In the field of Chemical Kinetics, terms like Molecularity and Order Of Reactions are often used. I am a bit confused between these two terms. Can someone explain to me about these two terms and ...
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3answers
214 views

Positive or Negative Anode/Cathode in Electrolytic/Galvanic Cell

In a galvanic (volatic) cell, the anode is considered negative and the cathode is considered positive. This seems reasonable as the anode is the source of electrons and and the cathode is where the ...
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2answers
600 views

By what mechanisms can molecules with the same empirical formula be so different?

I understand the difference between empirical and chemical formula. But I always thought that compounds and molecules took their specific shape because it's the lowest energy configuration. How then, ...
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1answer
63 views

What is the constant of integration in a series reaction in chemical kinetics?

I have a question regarding the rates for a series reaction in kinetics. So imagine $\ce{A -> B -> C}$, with $k_1$ as rate constant for $\ce{A -> B}$ and $k_2$ as rate constant for $\ce{B ...