Questions tagged [units]
For questions about the definition and usage of units of measurement.
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1answer
35 views
What is the ppm of this solution and how does one decipher what it means? [closed]
What is the concentration of a solution, in parts per million, if 0.02 g of NaCl are dissolved in 1000 g of solution?
I think it comes out to 20 ppm. I am confused on what ppm means tho. So 20 ppm ...
-1
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1answer
18 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
votes
1answer
31 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. ...
-2
votes
1answer
162 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
31 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
81 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
votes
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
votes
0answers
68 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 ...
-1
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1answer
35 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
57 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
votes
0answers
334 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
45 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.
1
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0answers
478 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
77 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
votes
2answers
150 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
72 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
36 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
246 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
709 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
91 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 ...
-5
votes
1answer
253 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
57 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
95 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
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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
559 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
votes
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
votes
0answers
51 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
votes
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
215 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
73 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
467 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
599 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
747 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
votes
0answers
166 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
40 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
116 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
679 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
844 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
8k 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
230 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
36 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 ...
2
votes
2answers
153 views
When you report Einstein units do you capitalize it?
When you report Einstein units do you capitalize it? Since we're using it in the context of a unit (and not a name) is capitalization necessary?
Example:
The measured value was reported as 10 ...
-1
votes
2answers
338 views
Number of picoseconds in a week is exact? [closed]
My chemistry textbook states that the number of picoseconds in a week is not exact because a week is defined by the Earth's rotation.
Does that also mean that 3600 seconds in an hour also isn't exact ...
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votes
1answer
6k views
What does mol L−1 mean? [closed]
I am researching how to Determination of Vitamin C Concentration by Titration for my science fair project and it says
Titrate the sample with $0.005~\mathrm{mol~L^{−1}}$ iodine solution. The ...
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votes
1answer
219 views
Wavelength of the emitted electron
Here is my attempt:
P.S: although I have ticked option C. That may or may not be the answer.
1
vote
1answer
294 views
Reaction rate unit conversion: how to convert from molarity to ppm
How can I convert a reaction rate $k$ with units of $\mathrm{1\over M~~s}$ to $\mathrm{1\over ppm~~s}$?
For context: I want to make a numerical simulation of a system of reactions that happens in air ...
