Questions tagged [units]
For questions about the definition and usage of units of measurement.
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Units of mass on the atomic scale
what are the systems of recording atomic masses and their units?
I know that the nucleon number is the number of protons and neutrons
I also know that the mass number on the periodic table is the ...
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Is 1 ppb equal to 1 μg/kg?
In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I ...
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What are the units of Kc and Kp?
They are both equilibrium constants as far as I know.
Kc is in terms of molarity and Kp is in terms of pressure. Also both of them are ratios of respective quantities [ ratio of molarity(s) in Kc and ...
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What is the correct unit for the equilibrium constant?
I have the following equation
$$K_a = \dfrac{c\alpha^2}{1-\alpha},$$
with units $c= \pu{mol/cm^3}$ and $\alpha$ is the same. I'm not sure how to get the correct units for $K_a$. What I have come up ...
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May I treat units (e.g. joules, grams, etc.) in equations as variables?
Suppose I have two units, Tonks, $T$, and Borks, $B$, as well as the equation $\frac{50T}{20B}=x$. May I manipulate the equation as though $T$ and $B$ were the kinds of symbols that we learned to ...
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Effects of Changing Avogadro's Constant
The Avogadro project suggests that we redefine the Avogadro constant to be equal to our best known estimate, $N_\mathrm{A} = 6.02214179 \times 10^{23}$, and redefine the kilogram based on the Avogadro ...
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Where does the label ‘Dq’ to denote the field split in coordination compounds come from?
As established in a previous question, coordination compounds typically have a field split between the $\mathrm{t_{2g}}$ and the $\mathrm{e_g}$ d-orbitals.[1] This energy difference can be explained ...
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Why a specific temperature for value of 1 calorie?
Everything in chemistry often comes with a strong reason and facts behind it, but I stuck in definition of $1$ calorie.
My reference book define one calorie as amount of heat required to raise the ...
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What are the units that measure free energy?
Is it $\pu{kJ/mol}$? I have done problems and I always end up with these units, but is this correct?
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How are lowercase m and uppercase M used in general chemistry courses? [closed]
Where do lowercase m and uppercase M make appearances in general chemistry, and what do they signify?
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What does the unit M stand for? [closed]
What does $\mathrm{M}$ signify in this pH calculation? To me, it just seems to be a random variable.
For example: $\ce{[H+]} = 1.0\times10^{-7}~\mathrm{M}$
I am not sure what the $\mathrm{M}$ is ...
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Is zero-point vibrational energy an intensive or extensive property?
The zero-point vibrational energy (ZPVE) is the non-zero amount of non-electronic energy that molecules have even at zero kelvin and is purely quantum mechanical in nature. For a molecule with $c$ ...
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What is the difference between the units 'torr' and 'mm of Hg'?
According to present definition torr and mm of Hg differ though slightly.
I am still confused over it. Can someone write an explicit answer differentiating between them and the reason for ...
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Can Rydberg constant be in joules?
In my textbook (Chemistry Part - I for Class XI published by NCERT), there is an equation for the energy of an electron in an energy state: $$E_n = -R_\mathrm H\left(\frac{1}{n^2}\right)$$ and there ...
user79725
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Amount of substance expressed in yoctomole units
I stumbled upon a couple of papers where amounts were expressed in yoctomoles ([ymol], $\pu{10^{-24} mol}$) and I find it somewhat bothersome as 1 ymol would correspond to about 60% of atom/molecule/...
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Which unit should I use for m/z?
I've written m/z 300 - 1100 Thomson in my paper, but the reviewer said that the Th is already deprecated. So in this case, should I write m/z 300 - 1100 Da? or something else?
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Units in modified Arrhenius equation?
The modified Arrhenius equation is used to express the rate constant in a chemical mechanism model I'm working with. The equations is as follows:
$$k_\mathrm{f} = A\times T^b\times\exp\left(-\frac{E_\...
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How to retrieve Dalton value from m/z value?
As I understand, Dalton (Da) is the standard way for representing mass unit. As for $m/z$, which is a specific notation for mass spectrometry, quoting for wikipedia:
This notation eases data ...
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What are the units of P and V when R is expressed in terms of J/(mol K)?
I have learnt the ideal gas equation $PV=nRT$. However, I have some doubts regarding the units of the quantities in this equation.
When we take the gas constant $R=8.314\ \mathrm{J\ mol^{-1}\ K^{-1}}...
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How is sulfuric acid with a concentration of 12 M also 72% w/w?
According to LabChem, $12~\mathrm{M}$ of $\ce{H2SO4}$ is $72~\mathrm{w/w\%}$.
When I try to convert $12~\mathrm{M}$ of $\ce{H2SO4}$ to $\mathrm{w/w\%}$ I get $117\%$ which is obviously wrong.
$$\...
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Do all conversion factors have an infinite number of significant figures?
I believe conversion factors have an infinite number of significant figures. They should be exact values; but not all of them are, are they?
I looked at a pdf document (via the Internet Archive) and ...
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Why is the equilibrium constant unitless? [duplicate]
I read that the equilibrium constant is unitless because the molar activities of each of the species are used in the equilibrium expression, not the actual concentrations themselves. I understand that....
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Is the kilogram still consistent with the old definition?
My old understanding was that a gram is the amount of mass in a cubic centimeter of water.
But then I recently learned that the second was redefined to be some 9 billion cycles of a Caesium atom. ...
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When was the amu renamed the dalton? [closed]
I taught chemistry for 30 years and never encountered the unit until I saw it on a juice bottle!
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How to convert ppm to g/m3?
I'm not very comfortable with chemistry and I need to convert $\ce{CH4}$ concentration values in $\pu{ppm}$ to $\pu{g/m3}$. Is that possible?
I've already researched a bit and realised that for water ...
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What is the dimension of Avogadro's constant?
What is the dimension of Avogadro's constant ($N_\mathrm{A}$).
On Wikipedia it says it is dimensionless, but in Nigel Wheatley's article (pdf) On the dimensionality of the Avogadro constant and the ...
user96130
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Are the units of mole of oxygen molecules the same with the units of mole of nitrogen molecules?
Suppose we have in a box $3 \,{\rm mol}$ $\ce{O}$ and $3 \,{\rm mol}$ $\ce{N}$. Is the addition of these two quantities meaningfull? We do it all the time when we want to find the molar fraction. I ...
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Up to which dilution can one assume that 1 mg/l = 1 ppm?
For aqueous solutions it is often assumed that 1 milligram per liter equals 1 ppm. Are there any guidelines up to which concentration this shortcut is admissible?
Are there any formulas which ...
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Why is gas pressure measured in mmHg?
Pressure can be measured in $\pu{mmHg}$ which is equal to the pressure exerted by a “column of mercury” of a height expressed in $\pu{mm},$ at $\pu{0 °C}$ under Earth’s normal gravity.
Does the ...
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How does the value of the equilibrium constant give information about the extent of reaction at equilibrium?
Pretty much everywhere I've read, the numerical value of the equilibrium constant gives you information about the relative concentrations of products and reactants in the equilibrium mixture; the ...
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