# Questions tagged [units]

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

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### 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 ...
91 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 ...
191 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 ...
1 vote
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### What is the unit of molar density?

I'm reading Unit operations of Chemical Engineering, 5th edition by Warren McCabe. They defined the "molar density $\rho_{M}$" as $\ce{\rho_{M}=\frac{n}{V}}$. The parameters $n$ and $V$ are ...
1 vote
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### 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 ...
1 vote
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### 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. ...
1 vote
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### 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 ...
1 vote
33 views

### Interlayer binding energy: how to convert to meV/Å²?

I've noticed that in most papers the interlayer binding energy is given in units of meV/Å². But how do I get these units? Do I divide the interlayer binding energy I get by the area of my unit cell?
1 vote
604 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 ...
1 vote
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### 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 $k$:  \...