Questions tagged [units]
For questions about the definition and usage of units of measurement.
0
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3answers
51 views
Conversion from a PPB value to µg/m3 of Isobutylene
I have a quite simple problem, found a lot of information about it, but I am not sure anymore if I do my calculations right.
I own a sensor, which reports measurements in isobutylene units as PPB. So ...
0
votes
0answers
11 views
Practical salinity scale (PSS or PSU) to salt concentration conversion [closed]
How do I calculate the concentration of salt in a sample, given its salinity in terms of practical salinity units (PSU)
EDIT: I may assume most of the salt is NaCl.
0
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1answer
18 views
Combination of several unit symbols when finding new pressure from ideal gas law
As a car is driven, the tires heat up and the volume and the pressure change. Calculate the new pressure of a 35.0 L tire initially at 235 kPa that expands to 36.5 L when it heats up from 15.0 °C to ...
0
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0answers
13 views
Is the negative excess volume of ethanol/water the cause of my math error?
I have a binary mixture, say ethanol at $90\%wt$ ethanol, $10\%wt$ water. According to Perry's Chemical Engineers' Handbook 9th Ed., that mixture has a density of $0.81797g/cc$ (at $20^{\circ}C$). ...
-1
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3answers
163 views
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 ...
0
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1answer
43 views
Confusion between moles and molarity units
I am a total newbie in the field and i would like some kind of guidance.
So, I have been recently given 2 datasets with measurements regarding several phospholipid fatty acids of plasma HDL. Both ...
-1
votes
1answer
22 views
Rate constant converion [closed]
I need to calculate the half life for a first order reaction for which I need the rate constant $k$. From literature I observed that for a very closely simulated experiment I obtained the numerical ...
0
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1answer
33 views
Converting pounds to grams [closed]
I wanted to figure out how many grams were to a lb and instead of looking it up I used my textbook and found 1 kg = 1000 g and 1 kg = 2.205 lb. I set up a cross multiplication equation to solve for x. ...
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1answer
278 views
What does atm•L mean? [closed]
In my chemistry book I always see a dot for units. For example, atm•L. Does this mean “1 atm per Liter?” By Atm I mean atmospheric pressure, not atom.
2
votes
1answer
33 views
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. ...
3
votes
1answer
84 views
Is it possible for me to derive Avogadro's number?
To my understanding the mole is the unit used to translate between mass on the atomic level and mass in the macro level, defined as the number of atoms in $12$ grams of Carbon-$12$, which apparently ...
24
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5answers
5k views
Why do we still need to know about the Rankine temperature scale?
I am learning process principles in chemical engineering and I was taught various temperature units like Fahrenheit, Celsius, Kelvin, and Rankine. I see the first three being used quite commonly, but ...
2
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0answers
71 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 ...
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1answer
39 views
Units for density in nanorod image
I am counting the number of nanorods contained in a sample (see picture below). The length scale is 1 µm. What units does the density have? Is it µm-2?
1
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0answers
66 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 /...
2
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0answers
452 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 ...
1
vote
0answers
57 views
is rydberg constant and rydberg unit are same? [closed]
i want to ask a question that.is rydberg constant and rydberg unit are same. UNIT OF RYDBERG CONSTANT IS m^-1, right? Then what is rydberg unit.
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0answers
723 views
What really are the units of enthalpy change? [duplicate]
A reasonable definition of standard enthalpy change of formation would be:
'The enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions'
...
1
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1answer
88 views
Calculate pressure equilibrium constant from concentration equilibrium constant
$$\ce{N2(g) + 3H2 (g) -> 2NH3(g)}$$
Calculate $K_\mathrm p$ from $K_\mathrm c$, given that $K_\mathrm c = \pu{4.2 M^-2}$
and that there is 0.2 moles of $\ce{N2}$, 0.6 moles of $\ce{H2}$ and 0....
2
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2answers
175 views
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?
0
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1answer
74 views
How isotopes atomic mass was defined?
So we say that 1 Amu (u) = 1/12 of the mass of a Carbon 12 atom.
Im not sure about this, but I believe that first we measured the mass of 1 carbon 12 atom (This includes the mass defects that occur ...
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1answer
38 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 ...
6
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2answers
249 views
In biochemistry, when do rate constant units matter in calculating free energy changes?
In my experience, it is always been the ratio of products to reactants that mattered, so as long as your units are consistent; what they are doesn't matter. However, an in-class problem today required ...
1
vote
1answer
910 views
What pressure units should be used when calculating electrode potential with Nernst equation?
Example 17: Calculate the electrode potential of given electrode
$$\ce{Pt,Cl2 (\pu{1.5 bar}) | 2 Cl- (\pu{0.01 M})}\,; \quad E^\circ_\ce{Cl2/2Cl-} = \pu{1.36 V}$$
Solution: The reaction of ...
3
votes
1answer
95 views
Order of the reaction between hemoglobin and oxygen
I have the reaction:
$$\ce{Hb + O2 <=>[$k$][$k'$] HbO2}$$
where $\ce{Hb}$ is hemoglobin, $k$ is the rate constant of the forward reaction, $k'$ is the rate constant of the inverse reaction. On ...
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votes
1answer
296 views
Concentration of ammonium phosphate if dissolved in water [closed]
If $\pu{2.54 mg}$ of ammonium phosphate is dissolved in enough water to make $\pu{300 mL}$ of the solution, what is the molar concentration of the solution?
The answer is $\pu{5.68e-5 mol L-1}$. ...
1
vote
1answer
59 views
Concentration of mercury in body
Symptoms of mercury poisoning become apparent after a person has accumulated $\pu{20 mg}$ of mercury. If a person ingested $\pu{30 mg}$ of mercury, what concentration of mercury in parts per million, ...
7
votes
2answers
3k views
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 ...
5
votes
1answer
102 views
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/...
3
votes
0answers
37 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 - ...
6
votes
1answer
564 views
Does adding prefixes to SI units make them no longer SI units?
Our chemistry professor said that "mg for mass, g/m3 for density, ms for time are all SI units".
I want to make sure now, even if we added a prefix to the unit, will it still be an SI unit?
3
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1answer
1k views
Freundlich Equation's dimensions
So, we have the Freundlich's Isotherm equation as $\frac{x}{m} = kp^{\frac{1}n}$, where the LHS measures the extent of adsorption with the corresponding pressure $p$ in the RHS with the two constants, ...
2
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0answers
55 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 ...
0
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1answer
37 views
What would be the unit for the calculation of the rate of reaction?
In a reaction between magnesium and hydrochloric acid, I measured the change in mass of the magnesium strip (Initial weight: 0.03g). I calculated the the time for the reaction to reach completion. A ...
4
votes
1answer
229 views
What's an “amagat”? How is it different from the Loschmidt Number?
At class, we were (briefly) taught about the Loschmidt Number/Constant ($n_0$), which isn't really different from the Wikipedia definition,
The Loschmidt constant or Loschmidt's number (symbol: $...
3
votes
0answers
74 views
Why does mmHg persist in organic chemistry? [closed]
In most areas of chemistry, standard units are adopted - we never would think to use ounces (even American chemists resist) BUT even in modern journals or textbooks, we commonly still see the unit <...
5
votes
3answers
470 views
What term should I use when I am quantifying the amount of matter, mass or weight?
I am writing an academic article but I got confused as I am writing about the weight a specific metal got by using balance scale. Should I use the term mass, which has a unit of kg, or weight, which ...
3
votes
2answers
2k views
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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1answer
2k views
nM or μM, which is more concentrated? [closed]
A study found that a particular herb fueled cancer at nM concentrations but actually inhibited cancer in μM concentrations. Which is the higher concentration, nM or μM?
14
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2answers
615 views
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 $c$ ...
0
votes
3answers
815 views
What does the universal gas constant represent? [closed]
In the formula $$V=\frac{nRT}{P},$$ when we say $R$ is $\pu{0.082 L atm//mol K}$:
What do we mean? Specifically what does $\pu{K}$ mean here? Also $\pu{mol k}$? and $\pu{L atm}$?
Can you simplify it ...
4
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0answers
177 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 ...
0
votes
1answer
41 views
Expressing solubility in binary solvents with non-additive volumes
I have experimentally obtained data that shows the molarity of a saturated solution in mixed solvents, with different proportions of solvents.
The issue here is that the two solvents (water/ethanol)...
5
votes
2answers
122 views
Force Fields and units
I am a math student trying to implement a simple force field in python for determining the energy of a small molecule and trying to minimize it in order to find a stable configuration. I was wondering ...
4
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0answers
724 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 ...
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votes
1answer
960 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 ...
0
votes
1answer
1k views
Unit conversion of Molar Conductivity
I know this might be a silly question but I am confused with different answers of internet. My question is:
Molar conductivity is given as:
Molar conductivity = $k÷M$.
SI unit of :
k is S/m & ...
0
votes
1answer
9k views
How to use C1V1=C2V2 How do the units work?
I am trying to do a dilution where I know I have 0.749 g/ mL and I want to use this concentration to calculate the grams of aspirin in each 100 mL solution. I am specifically worried about the units. ...
3
votes
3answers
238 views
Is the amount of cubic inches in a cubic foot exact?
I know we are supposed to use SI units and I know they are defined very well.
But does that mean that Imperial units of length/volume aren't exact? Don't they have infinite significant figures in ...
1
vote
1answer
37 views
How to convert the D'Arcy and Watt model from activity to concentration in mol/m^3
The D'Arcy and Watt 1970 model in "Analysis of sorption isotherms of non-homogeneous sorbents" for water adsorption is as follows:
$$W = \frac{KK'a}{1+Ka} + ca + \frac{kk'a}{1-ka},$$
where:
$W$ is ...
