Skip to main content

Questions tagged [units]

For questions about the definition and usage of units of measurement.

27 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
4 votes
0 answers
586 views

What does “at%” mean and how it differs from “mol%”?

Sorry if my question is a bit obvious, but for some reason I'm getting confused with the percentages in this question: Concentration of $\ce{A}$ is $\pu{80 at\%}$ and concentration of $\ce{B}$ is $...
dareToDiffer07's user avatar
4 votes
0 answers
234 views

Difference between change in energy level and hyperfine energy level?

The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom. --> This ...
PandoraU.U.D's user avatar
4 votes
0 answers
2k views

What do we have both r.a.m. and r.m.m.?

Read Orthocresol's answer here first: What is the difference between "molecular mass", "average atomic mass" and "molar mass"? Orthocresol, in his answer, says that ...
MrAP's user avatar
  • 775
4 votes
0 answers
633 views

Calculating volume ethanol in an fermented aqueous solution of sucrose, water, and ethanol

I've been working on a biology experiment where I calculate the fermentation yield of yeast under various light induced stress responses inhibiting the translation of various fermentation enzymes. My ...
Mikey G's user avatar
  • 41
3 votes
0 answers
50 views

Could the loss of mass in the kilogram be due to oxidation?

I was wondering about this. I have heard, and known for a while, that the famous and celebrated Prototype Kilogram - the lump of metal whose mass is used to define the standard mass scale worldwide - ...
The_Sympathizer's user avatar
3 votes
0 answers
738 views

ppm as hexane/propane/methane etc

This question is primarily related to stack testing data. Whenever stack testing is being conducted and the parameter being measured is VOC concentration, it is often reported as ppm (as hexane) or ...
Ryan_C's user avatar
  • 185
2 votes
1 answer
1k views

What is the unit of molar density?

I'm reading Unit operations of Chemical Engineering, 5th edition by Warren McCabe. The authors defined the molar density as $\rho_{M} = \frac{n}{V}$. Here, $n$ and $V$ represent the number of moles ...
kamikaze's user avatar
2 votes
0 answers
242 views

What is the name of the physical quantity that is given in kJ/g?

The chemical potential $\mu$ of a pure phase corresponds to the Gibbs free energy $G$ divided by the amount of substance $n$: $${G\over n} = \mu,$$ so the units of $\mu$ are $\pu{kJ mol^-1}.$ What do ...
La Cordillera's user avatar
2 votes
0 answers
111 views

Why was the unit micrometers spelled backwards in old research papers?

I have recently been doing a literature research project on polymers and have been reading a lot of papers from the 1950s and 1960s (mostly in American journals from American authors). I saw this ...
iammax's user avatar
  • 1,009
2 votes
0 answers
317 views

How to convert from ppm to ug/m3 in case of PMx?

For $\text{PM}_{10}$, $\text{PM}_{2.5}$ sensors, sensitivity, minimum and maximum recordable concentrations are generally expressed in $\pu{ppm}$ (parts per million) while legislation uses $\pu{\mu g /...
Francesco Boi's user avatar
2 votes
0 answers
2k views

Conversion of a permeability value from barrer to SI unit

I have done a permeability experiment on LDPE in the presence of air. At $\pu{30^\circ C}$, the permeability was found to be 1.846 barrer. Now I am trying to apply this permeability value to a ...
I.vdM's user avatar
  • 31
2 votes
0 answers
96 views

TINKER molecular modeling extra forces - energy unit

I use the TINKER molecular modeling software package (version 7.1.2) for computational physical chemistry. There is an extra file (extra1.f) included for the user to edit and incorporate their own ...
d.conors's user avatar
2 votes
1 answer
334 views

What is the correct method for converting a concentration given in ppm to molarity?

I need to convert a concentration of dissolved boric acid $(\ce{H_3BO_3})$ in water (at high temperature and pressure) from ppm to mol/L. Concentration of boric acid: $c_{ppm}=1500\ \ce{ppm}$ Molar ...
qwebfub3i4u's user avatar
1 vote
0 answers
33 views

Why isn't the rate of an elementary reaction expressed in activity?

Why don't chemists use $r_\ce{X}=\frac{\text{d}a_\ce{X}}{\text{d}t}$ where $a_\ce{X}$ is the chemical activity of species $\ce{X}$ and corresponding rate law for elementary reactions as $r=ka_1^{\...
megamonster68's user avatar
1 vote
0 answers
76 views

Units of collisional cross-section and reactive cross-section

I haven't been able to find the units of the reactive cross-section (σ* = Pσ) online but when I do a unit analysis from the equation: $$ k = PσN_A √(\frac{8k_BT}{πμ}) e^{-E_a/RT}$$ then when plotting ...
katara 's user avatar
  • 1,095
1 vote
0 answers
123 views

Why isn't entropy dimensionless?

The usual units are J/K, however the only reason temperature has different units than energy is because we didn't used to know temperature was just the average kinetic energy of atoms/molecules. ...
Mikayla Eckel Cifrese's user avatar
1 vote
0 answers
32 views

Thermochemistry: On Units of Enthalpy Change and Implicit Given of Initial Temperature of Calorimeter

I would like to ask two separate questions. But first, so that we are on the same page, the experiment used a constant-pressure calorimeter, and it is a neutralization reaction of 1M of HCl and 1M of ...
g1lb3rt0123's user avatar
1 vote
0 answers
36 views

Interlayer binding energy: how to convert to meV/Ų?

I've noticed that in most papers the interlayer binding energy is given in units of meV/Ų. But how do I get these units? Do I divide the interlayer binding energy I get by the area of my unit cell?
DykFlint's user avatar
1 vote
0 answers
184 views

Rate constants using Arrhenius equation

If I'm trying to use the Arrhenius equation in this form: $$\ln\left(\frac{k_2}{k_1}\right) = -\frac{E_\mathrm a}R\cdot\left(\frac1{T_2}-\frac1{T_1}\right)$$ And I am given the activation energy ($...
atreyav's user avatar
  • 11
1 vote
0 answers
48 views

How much CO2 is produced by plant litter?

I made measurements of CO2 formed during decomposition of dead plant material using gas spectrometer. It gives the results of CO2 in ppm. How do I convert it to $\large \rm \frac{mg~CO2}{\text{1 g ...
iirisa's user avatar
  • 11
0 votes
0 answers
53 views

Comparison of oxygen and carbon-12 as standards for mass

While studying about the standards of atomic and molecular mass, I have learnt that while initially hydrogen was used as a standard of mass (its mass taken as unity), according to my book, oxygen was ...
Smarika Singh's user avatar
0 votes
0 answers
41 views

How to rewrite kinetic mass balance to get to proper SI units?

Suppose from kinetic mass balance I get the following differential equation of the molarity substances $A$,$B$, and $C$ in a reactor, with molar in- or outflow rate $\phi$, and rate constant $k$: $$ \...
user313866's user avatar
0 votes
0 answers
106 views

How to convert from dipole derivative to atomic units?

I need to convert dipole derivative output by Gaussian into atomic units. The dipole derivative is given in Gaussian in the weird units $(\mathrm{km/mol})^{1/2}$. I know that $\pu{1 D^2/(Å^2amu)}$ = $\...
poisonDartFrog's user avatar
0 votes
0 answers
33 views

When multiple sources give the content of an ingredient my an unqualified percentage, can I safely assume this is by weight? Or; it's not a wart

I am trying to make a simple scented shampoo and body soap for my own use and for Christmas gifts. I statr with a base of 32 oz – (a bit under a kg) of a mild commercial castille soap (Dr. Bronner’s ...
andrewH's user avatar
  • 167
-1 votes
1 answer
48 views

Should I relate the number of moles between substances when converting weight units?

Good day! I graduated from an undergrad degree of chemistry almost 3 years ago but I'm frustrated that I fail to reconcile these things: In gravimetric analysis, to get the correct amount for the ...
Iceheat's user avatar
-1 votes
1 answer
4k views

Why are absolute entropies given the units J mol−1 K−1?

I've just started looking at the concept of entropy and can't understand why absolute (or standard molar entropies) are given the units $\pu{J mol^−1 K^−1}$. Could someone explain the rationale for ...
Tom Brooks's user avatar
-2 votes
1 answer
72 views

Convert the lowest IR wavelength to energy in J, frequency in Hz, and wavenumbers in cm-1

Look up the range of wavelengths in nm in the IR region of the electromagnetic spectrum. Convert the lowest IR wavelength to energy in J, frequency in Hz, and wavenumbers in cm-1. I think I’m going ...
user57797's user avatar