# Tag Info

43

Looks like in 1966 there were still residues of double prefix notation in use. Here's an entry from Russ Rowlett's compilation of units on ibiblio.org (Rowlett): millimicro- (mμ-) an obsolete metric prefix denoting 10-9 or one billionth. This prefix has been replaced by nano- (n-). Here's what is noted on wikipedia: Double prefixes Double prefixes have ...

8

Simple and actual answer: The current definition of Avogadro's number doesn't depend on the unit of mass. They are completely independent quantities. The Avogadro's number is currently simply defined as $\pu{6.02214076e23}$. It's just a number which is important enough to get a special name. The answer you are probably looking for: Historically the Avogadro'...

5

Using the ideal gas law $$pV = nRT = \frac{m}{M}RT$$ you can express the density $\rho = \frac m V$ in terms of molar mass, pressure, ideal gas constant, and temperature: $$\rho = \frac{pM}{RT}$$ With the units you use in your second example, this yields a density in $\mathrm{g\,m^{-3}}$, whereas you insert a density in $\mathrm{kg\,m^{-3}}$ into your ...

4

The physical reason why the dimensions of k differ for different reactions is the different mechanism behind the reaction. A process that only involves the internal vibration or rearrangement of one species differs from a process in which two or more equal or different species must first diffuse and collide*. It seems intuitive to me that this should be ...

4

Maybe it would make more sense if rate constants would have different symbols depending on whether it is a zero, first or second order reaction. As an analogy, we might be asking "how big" an object is depending on the length of it. Depending whether the object is, say, a square, a cube or a hypercube, the answer would be in terms of its area, ...

4

I think the clinical chemistry notation has not been standardized but certainly it has been inspired by chemists. The capital M in mosM emphasizes that it is milliosMolar. Chemists use capital M to denote molarity. On the other hand, mosm indicates milliosmolal. Chemists use small m to symbolize molality. This notation is not universal. From this slightly ...

3

“[M]ass is the amount of "matter" in an object (though "matter" may be difficult to define), whereas weight is the force exerted on an object by gravity.” (Wikipedia quoting [de Silva, G.M.S. (2002), Basic Metrology for ISO 9000 Certification, Butterworth-Heinemann, 214p.] Well-known relationship: $$W = m \times g$$ where W is weight, m ...

3

Recall that $\Delta G^\circ$ represents the difference in Gibbs free energy between an equilibrium state and a "standard state." This standard state is completely arbitrary, and the definition has changed slightly over time. Currently, IUPAC defines it as having all dissolved substances at a concentration of 1 mol/L and all gases at a partial ...

3

You have mixed up Avogadro number $N_0$ with Avogadro constant $N_\mathrm{A}$, and used the constant to define itself, which is incorrect mathematically. Analytical form of your suggestion is as follows: $$N_\mathrm{A} = N_0\cdot\pu{mol^-1} \label{eqn:1}\tag{1}$$ $$\implies \pu{1 mol^-1} = N_\mathrm{A}\cdot N_0^{-1} \label{eqn:2}\tag{2}$$ Plugging \eqref{eqn:...

3

It is a good question which has already been somewhat addressed in the 1880s. This "field" was called quantity calculus. Calculus here is not the integration / differentiation, but rather the Latin calculus implying a method of calculation. There is a very nice article "Quantity Calculus: Unambiguous Designation of Units in Graphs and Tables&...

3

Maybe a numerical example may help you compare the different orders. Let's take first an example of a reaction of zeroth order : the combustion in air of a candle containing $n$ $mol$ wax. At every second, the same amount of wax is burned. The rate of the reaction is $$r = -\frac {dn}{dt} = k_o·n^0 = k_o$$ If the candle contains $1.44$ mole wax and burns in $... 2 Well, it may not be appropriate to say that the rate constant, k, has no physical meaning. It is the only factor in the rate equation which is temperature dependent, so larger k means faster rate of reaction. Another way of looking at the units of k is in terms of Arrhenius equation. $$k(T)=A e^{-E_{\mathrm{a}} / R T}$$ The factor$A$is called the ... 2 The simplest way to approach this is that the rate constant has whatever units that make the rate have the correct units. Generally, the rate is in units of molar per second, so based on how you're multiplying concentrations (in molar) in the rate law, you should be able to figure out the appropriate units for the rate constant. 2 Judging from the following table consisting of compiled notations presented in offline edition of The ACS Style Guide and AMA manual of style, section 13.12 Units of Measure: $$\begin{array}{ll} \hline \text{Unit of measure} & \text{Symbol} & \text{Ref.} \\ \hline \text{osmolar} & \text{osm (also osM, Osm)} & \text{[1, p. 191]} \\ \text{... 1 The equilibrium constant has to be dimensionless otherwise expressions such as \Delta G^0=-RT\ln(K) are not possible. In a reaction such as$$\ce{A_2 <=> 2A}$$if \alpha is the degree of dissociation and 1-\alpha of A_2 reacts and 2\alpha of A is produced using the partial pressures (P_A=2\alpha P/(1+\alpha); P_{A_2}=(1-\alpha)P/(1+\alpha))... 1 Yes you can't compare extent of reactions directly based on the numerical value of the equilibrium constant. A very good example of this is the comparison of solubility of different salts based on their solubility products. Let's take the example of calcium and silver carbonates:$$ \begin{array}{|c|c|c|} \hline \text{Salt} & K_\text{sp} & \text{... 1 Changing temperature doesn't change the mass of a fixed amount of a substance. But it does change the density. So a 10mL sample of water at 25 celcius will still contain the same amount of substance at 10 celcius. But it will not longer occupy exactly 10mL, but will be a slightly smaller volume. Since you specified the conditions as having fixed volume, you ... 1 The energy is the potential energy of all electrons in the molecule. Sometimes the term also includes the potential energy of the nuclei but in most cases it doesn't. As reference or zero energy you can imagine the case where the electrons are non interacting or infinitely far apart from each other. In this sense it tells you the energy required to "... 1 Collected and elaborated info from the chat with the OP: To summarize the osmolality and tonicity difference, elaborated in the below link: Osmolality takes into account all solutes. Tonicity excludes solutes able to pass the semipermeable membrane. So isotonic solutions need not to have the same osmolality. The osmotic pressure is caused by decreased ... 1 Maybe some numerical values may help. Radioactivity. The activity is the number of disintegrations occurring per second in a given source. The unit is the Becquerel :$1 Bq = 1 s^{-1}$. For example, the experience shows that$3.7·10^7$nucleus are decomposed per second in$1$g$\ce{Ra-226}$. The activity of$1$g$\ce{Ra-226}$is$3.7·10^7 Bq\$ which was ...

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