2015年1月7日 · The problem was that physics stuck to isotopically pure O-16 for their mass scale, and chemistry used "oxygen" (i.e., with some O-17 and O-18 present). There's 0.028% difference between those scales. That may not sound like much, but with molecules of ~200-500 amu, it starts to add up.

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2017年6月21日 · The equation below represents combustion of methane ($\ce{CH4}$, $\pu{16.04 g/mol}$). Balance the equation, and calculate the mass of water ($\pu{18.02 g/mol}$) formed when $\pu{40.0g}$ of methane is burned. $$\ce{CH4(g) + O2(g) -> CO2 + H2O(g)}$$ I have started the problem by balancing: $$\ce{1CH4(g) + 2O2(g) -> 1CO2 + 2H2O}$$

2017年5月4日 · Examples include $\ce{^{12}C}$, $\ce{^{16}O}$ and $\ce{^{32}S}$. All other nuclei are NMR active: Odd/Odd. Nuclei that contain an odd number of protons and an odd number of neutrons have I that are positive integers. Examples include $\ce{^2H}$ $(I=1)$, $\ce{^{14}N}$ $(I=1)$ and $\ce{^{10}B}$ $(I=3)$. Odd/Even & Even/Odd.

2018年7月8日 · The graph of binding energy per nucleon (Hyperphysics) seems to peak at Iron-56. However, Wikipedia says that Nickel-62 has the highest binding energy per nucleon of any known nuclide (8.7945 MeV)....

2022年8月30日 · So the covalent binding energy expected for the proposed $\ce{O#O}$ triple bond in the gas phase would be insufficient to overcome the repulsion between two positive charges, and we should expect the proposed $\ce{O2^{2+}}$ ion to be less stable than a pair of single $\ce{O^+}$ ions.

2020年7月6日 · Chemists choose to define the amu as 1/16 of the average mass of an oxygen atom as found in nature; that is, the average of the masses of the known isotopes, weighted by their natural abundance. Physicists, on the other hand, defined it as 1/16 of the mass of an atom of the isotope oxygen-16 ($\ce{^{16}O}$). $^1$ unified atomic mass unit(u)

2021年4月21日 · The simplest and most direct explanation is that isotopically heavier molecules have higher boiling points. Regular water (R) boils at 100.0 $^o$ C. Heavy water (H) boils at 101.4 $^o$ C. A mixture of the two (R + H) can be separated by a distillation column. The heavier molecules require more energy to evaporate, to push away one atmosphere.

2014年6月20日 · $\begingroup$ @Martin that is a good point, but I think that for the most part 'amu' is understood to be the unified atomic mass unit based on carbon-12, not oxygen-16. I at least have always seen 'amu' and not 'unified amu' in publications within the last couple of decades. $\endgroup$

2018年2月20日 · For water, the temperature of the triple point (273.16 K) is remarkably close to its freezing point at atmospheric pressure (273.15 K). Because 0 °C was originally defined as the freezing point of water, instead of changing the zero point when they redefined the scale based on absolute zero and the triple point, they decided to define the ...