Questions tagged [units]

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

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9
votes
3answers
531 views

Units of rate constant (cycles per second vs radians per second) in Eyring equation

In the Eyring equation (EE), $$k = \frac{k_\mathrm B T}{h} \exp\left(\frac{-\Delta G_{\mathrm f}}{RT}\right),$$ the units of $k$ are $\mathrm{s^{-1}}$. However, in general rate constants are usually ...
4
votes
0answers
488 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 ...
2
votes
1answer
102 views

Pressure change of a gas upon increasing the temperature

My assignment is as follows: A sample of air is trapped in a container at 16.2 psi. If the initial temperature is increased from 10°C to 32°C, what is the final pressure? I am really confused as ...
-2
votes
1answer
749 views

Reaction rate constant conversion [closed]

I'm flustered, I'm not into chemistry and need to convert $\mathrm{(nM\cdot s)^{-1}}$ to $\mathrm{(M\cdot s)^{-1}}$. Is it correct to multiply with $10^9$?
1
vote
1answer
5k views

How dangerous is a megacurie (MCi)?

I was researching the Kyshtym (nuclear) Disaster, and it said that it released 20 MCi (20 megacuries) of radiation into the air in a dust cloud. I read from this Yahoo Answers answer that: The ...
3
votes
1answer
14k views

Convert from Pa to Pa to J/dm^3 [closed]

Given the value 380 PaK^-1, how do I convert Pa to Jdm-3? I know that 1 joule = 1 Nm, and that 1 pascal = 1 N/m^2. But where does the dm^-3 (or L) come into this? I don't know where to start.
4
votes
3answers
490 views

What is the physical quantity/magnitude of pH?

I have a database to classify variables/parameters in water resources as follows: Variable: Precipitation (P); Quantity: Length; Units of measurement: mm (millimeters). Following the example, what ...
1
vote
1answer
206 views

Find the displacement of mercury in a vertical tube

So we have a 1m tube sealed at both ends. It is initially horizontally placed and the middle 0.1m contains mercury and the two ends contain air. Now the tube is turned vertical, we have to find the ...
4
votes
1answer
1k views

Do ALL conversion factors have an infinite number of sigfigs?

Conversion factors have an infinite number of sigfigs, right? They should be exact values; but not all of them are, are they? I looked at http://www.webassign.net/question_assets/buelemphys1/...
3
votes
1answer
5k views

How is the unit of measure “equivalent” abbreviated?

I usually use "eq" but I have been told to use "equiv." in order to avoid confusion with "equation". Is there a reference I can check?
3
votes
3answers
967 views

Is 44.5 mg/L a measurement of weight or volume?

I have a test result that I am trying to fully grasp. I need to determine how much of a contaminant I need to reach that amount in 4,800 gallons. Making the conversion to liters is no problem, nor is ...
7
votes
1answer
1k views

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_\...
4
votes
1answer
911 views

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 ...
33
votes
6answers
3k views

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 ...
2
votes
1answer
587 views

Unit of time used in rate law equations

If doing a problem where you use the integrated rate law for a second order reaction ($\frac{1}{[\mathrm{A}]}-\frac{1}{[\mathrm{A_0}]}=kt$) to first find $k$, then use that to find the half-life. ...
14
votes
1answer
26k views

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 ...
2
votes
3answers
2k views

Why does 1 cubic meter = 1000000 cubic centimeters?

I have the SI chart in front of me. It states that a centi is 10^-2 and since they are already designated cubic meters why does 1 cubic meter equal 1000000 cubic centimeters?
3
votes
4answers
10k views

Why is the units of kcat 1/s?

I understand that $k_\text{cat}$ measures the turnover number of an enzyme. This measure is therefore a quantity of molecule conversions per unit of time. I suspect that my problem is more that of a ...
4
votes
4answers
32k views

What does the ‘−1’ superscript mean in units?

For example, the rate of a chemical reaction can be expressed in $\mathrm{mol}/\mathrm{L}^{-1}/\mathrm{sec}^{-1}$. Why is it ‘−1’ and not, say, ‘−2’? Does it change the meaning if the minus is removed ...
4
votes
2answers
4k views

SI Units for Isothermal Incompressibility and Specific heat capacity at constant volume

I am looking for the SI units of isothermal incompressibility and specific heat capacity at constant volume. What I found was that isothermal compression was measured in " $\mathrm{m^2}\ \mathrm{N^{-...
2
votes
1answer
984 views

Using Conversion Factors

In Europe, gasoline efficiency is measured in $\mathrm{km/L}$. If your car's gas mileage is $35.0~\mathrm{mi/gal}$, how many liters of gasoline would you need to buy to complete a 142-km trip in ...
3
votes
2answers
2k views

Atomic Mass of ¹²C before 1961

Question: Prior to 1961, the atomic mass unit was defined as 1/16 the mass of the atomic mass of oxygen; that is, the atomic mass of oxygen was defined as exactly 16 amu. What was the mass of ...
2
votes
1answer
313 views

How to convert cm² to km²?

I have a problem that says "a small hole is $20.7~\mathrm{cm^2}$ wide. What is the area in $\mathrm{km^2}$." I started doing it like this: $20.7~\mathrm{cm^2} \cdot 0.01~\mathrm{m^2} / 1~\mathrm{cm^...
-4
votes
2answers
4k views

Why is it written as “joule” and “J”? [closed]

Why is the unit joule is written as "joule" and "J", I mean what does "J" mean and what does "joule" mean.
0
votes
1answer
878 views

Molarity to Percent, Mole Fraction, Molality

I have a series of questions similar to the following. I want to make sure I do this correct before I do the others. I am in need of a hint. ...
5
votes
2answers
315 views

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}}...
6
votes
1answer
1k views

What units do I use for energy in the Boltzmann distribution?

I am a mathematics student doing a course in thermodynamics and am working on the basics now. The question I am asked is: Suppose two states differ in energy by one electronvolt. What can be said ...
4
votes
1answer
839 views

How to find the units of the rate constant?

Consider the reaction $$\ce{2A + B -> Products}$$ When the concentration of $\ce{B}$ alone was doubled, the half-life did not change. When the concentration of $\ce{A}$ alone was doubled, the rate ...
2
votes
1answer
168 views

What does this scale mean?

$$\log_{10}~\mathrm{pg}/\mathrm{ml}$$ I do not understand the scale. How do I convert this to a standard concentration (without the logs)?
4
votes
1answer
746 views

How to compute the residence time for given flow rate in standard cubic meters?

I'm given a flow rate of a gas mixture of $3\ \mathrm{Nm^3/h}$ in standard cubic meters through a cylinder of length $50\ \mathrm{cm}$ and cross section $70\ \mathrm{cm^2}$, can I compute how long a ...