Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
57

As other answers have noted, the only gas lighter than helium is hydrogen, which has some flammability issues that make it more difficult to handle safely than helium. Also, in practice, hydrogen is not significantly "lighter" than helium. While the molecular mass (and thus, per the ideal gas law, the density) of hydrogen gas is about half that of helium, ...


48

Actually, hydrogen is the only gas that is lighter than helium. However, it has a very big disadvantage: It is highly flammable. On the other hand, helium is almost completely inert - this is why it is very much safer to use the latter. What might happen when you use hydrogen instead of helium was impressively proven by history when the "Hindenburg" ...


34

It depends on which definition of acids and bases you are using. According to the Arrhenius theory, acids are defined as a compound or element that releases hydrogen (H+) ions into the solution. Therefore, there are no Arrhenius acids without a hydrogen atom. According to the Brønsted–Lowry acid–base theory, an acid is any substance that can donate a ...


28

The two hydrogens are the same, but some periodic tables show hydrogen in both places to emphasize that hydrogen isn't really a member of the first group or the seventh group. Hydrogen is a diatomic gas in it's elemental state, which is different from the other group one metals (and similar to the group seven elements). At the same time, hydrogen usually ...


26

Harold Urey and George Murphy used spectroscopy to identify deuterium late in 1931, announcing it at the 1931 Christmas meeting of the American Physical Society. Picking up out of 'From Nuclear Transmutation to Nuclear Fission, 1932-1939" by Per F. Dahl: If anything, the naming of the new isotope proved more problematic than its isolation. At a special ...


25

In addition to the reasons ste listed, the isotopes of hydrogen have the greatest differences in mass compared to other elements. Consider that deuterium is twice as heavy as protium, and tritium is three-times as heavy as protium. Isotopes of all elements can be used in kinetic isotope experiments. The dramatic differences in mass among the hydrogen ...


22

We are discussing the following equilibrium We can make the acid a stronger acid by pushing the equilibrium to the right. To push the equilibrium to the right we can destabilize the starting acid pictured on the left side of the equation, and \ or stabilize the carboxylate anion pictured on the right side of the equation. Comparing acetic acid ($\ce{R~ =...


21

Water, as you may know, has a dualist nature between covalent and ionic bonding; oxygen is the second most electronegative element in the periodic table, while hydrogen's simplistic construction makes it very zen about how it forms bonds (it defines the center point of most electronegativity scales). While the bond between the hydrogens and oxygen of a water ...


21

There is no chemical difference, only a psychological one: how do you think about it. They are both the same thing, but many people associate $\ce{H+}$ ions with chemical reactions and protons with particle physics. A hydrogen atom has one electron and a proton, no neutron. Therefore $\ce{H+}$ is just a proton. That is why acids are sometimes referred as ...


21

It can't work because of the fundamental thermodynamics What you are proposing is, basically, the plane carries water; the water is broken down into its components, hydrogen and oxygen; the components are recombined by burning them as fuel. Burning hydrogen and oxygen is a perfectly good way to create a lot of heat. But it doesn't much matter how you break ...


20

As you have said, you are studying stoichiometry at High School Level. From this I can guess, that you have probably not studied the concept of Limiting Reagent yet. What is Limiting Reagent? In a chemical reaction, the limiting reagent, also known as the "limiting reactant", is the substance which is totally consumed when the chemical reaction is ...


18

Yes, sodium metal is also going to react exothermically with salt water or any other aqueous solution as long as it comes in contact with water: $$\ce{Na (s) + H2O -> Na+ (aq) + OH- (aq) + 0.5 H2 (g)}$$ eventually leading to explosion of hydrogen-oxygen mix forming near the water surface. Presence of sodium chloride in salt water isn't going to ...


17

First, let me say that I've enjoyed many times exploding soap bubbles of about one milliliter filled with hydrolysis gas. That is 1 cubic centimeter. That will give you a sound that rings in your ears in a decent sized living room. You may wish to use ear protection for the experiment. 50 ml will have an effect in a lecture hall that not only wakes up ...


17

This post deals with the mechanism that is observed in the gas phase. It is of course not as simple as the equation might suggest and you did suspect that already. $$\ce{2H2 + O2 -> 2H2O}$$ This will be divided into many different elementary sub reactions. Any mixture of oxygen and hydrogen is metastable (stable as long as you do not change the ...


17

I think there are two reasons. First, it is more convenient to categorize them under the actual element-name to which they belong. If I say "15-Beryllium" everyone knows immediately, what I'm talking about. If we add hundreds of isotope-names, it would be quite a mess. Leading to the second reason: Xenon for example has over known 30 isotopes. There are just ...


17

Your chemistry teacher is making a few simplifications there that make the statement false on a black-and-white true-and-false scale. Protons would repel each other electrostaticly due to their same charges. Neutrons interact with protons by the so-termed strong interaction (because it is stronger than the weak interaction; props to physicists for inventing ...


16

Yes free $\ce{H+}$ ions, protons, really exist. Protons are constantly emanating from the sun and reaching Earth. The proton flux is continuously monitored by satellite. However, in a solution such as water, instead of bare $\ce{H+}$ ions, they are $\ce{H3O+}$ or larger ions such as $\ce{H5O2+}$ or $\ce{H9O4+}$. When $\ce{HCl}$ dissolves, the ...


16

This is a rather interesting question because these names actually refer to classes of reactions (specific to certain reagents and products), and aren't constrained by specific proportions of substances or even the identity of these substances. $\hspace{4cm}$ A Rosenmund catalyst is used to reduce acyl chlorides to their corresponding aldehydes, and is ...


15

As the electrons fall from higher levels to lower levels, they release photons. Different "falls" create different colors of light. A larger transition releases higher energy (short wavelength) light, while smaller transitions release lower energies (longer wavelength). The visible wavelengths are caused a by single electron making the different ...


15

$\ce{Pd}$ can dissociate $\ce{H2}$ because the resulting $\ce{Pd-H}$ bonds are more stable than the starting $\ce{H2}$. But the reason why $\ce{Pd}$ is so good at dissociating $\ce{H2}$ is related to the energy barrier to bond formation. The dissociation of $\ce{H2}$ on a $\ce{Pd}$ surface (and on $\ce{Pt}$ and maybe several other metals) has no barrier. So ...


15

Water has formula H2O. Oxygen has 3 stable isotopes (99.76% 16O, 0.039% 17O, 0.201% 18O), and hydrogen has two (99.985% 1H, 0.015% 2H). Thus, there are 9 natural isotopic configurations for water: 3 possibilities for oxygen, multiplied by 3 possibilities for 2 hydrogens with 2 possible isotopes. Out of those 9 possible configurations, only 4 have a natural ...


15

Is your book by chance very old? From the Wikipedia entry for "nascent hydrogen": Nascent hydrogen is purported to consist of a chemically reactive form of hydrogen that is freshly generated, hence nascent. Molecular hydrogen ($\ce{H2}$), which is the normal form of this element, is unreactive toward organic compounds, so a special state of ...


15

WHAT MAKES HYDROGEN ABUNDANT IN UNIVERSE: After few minutes of creation of the universe, protons and neutrons began to react with each other to form deuterium, an isotope of hydrogen. Deuterium, soon collected another neutron to form tritium. Rapidly following this reaction was the addition of another proton which produced a helium nucleus. Sources say ...


15

There are quite a number of theories regarding acidity and basicity, but in this case, will explain the Lewis acid. The Lewis Theory of acids and bases This theory extends well beyond the things you normally think of as acids and bases. The theory An acid is an electron pair acceptor. A base is an electron pair donor The Lewis acid-base theory explains ...


12

A water molecule is charge neutral because there is the same number of positive charges as there are negative charges. In this diagram, called a Lewis structure, the dots represent electrons while the lines or dashes represent a covalent bond of two electrons. When water ionizes one of the hydrogen atoms absconds with itself and leaves it's electron ...


12

No, deuterium is completely stable. I found the answer at Hyperphysics, and it has to do with the mass energies of the products and reactants of this hypothetical reaction. The decay of deuterium would be $$\ce{D -> P + N + e + \bar{\nu}}_e$$ where $\ce{D}$ is deuterium, $\ce{P}$ is a proton, $\ce{N}$ is a neutron, $\ce{e}$ is an electron and $\ce{\bar{\...


12

The way I understand it is (and my understanding is by no means perfect, or complete), as you pointed out correctly: a hydrogen ion is in fact a proton. The proton is a "bare charge" and as you rightly said, "tiny". a This makes it extremely reactive (in a sense), and thus in a chemical system of any sort would immediately seek out and associate with the ...


12

Hydrocarbons are in fact the main source of hydrogen gas. According to Wikipedia, 95% of all hydrogen is produced by the steam reforming reaction: $$\ce{CH4(g) + H2O(g) -> 3H2(g) + CO(g)}$$ This is a very important industrial process which has been studied in depth. It is done at very high temperatures (~1000 °C) and under pressure (~20 atm), and can be ...


12

The effect is due to the symmetry properties of the rotational energy levels and those of the nuclear spin. The change with temperature is, as usual, traced back to the Boltzmann distribution. In homonuclear diatomic molecules such as $\ce{H2}$ it is necessary to consider the spin of the overall wavefunction to exchange of nuclei. If this is $\Psi = \psi_t\...


12

It seems like an idea of using magnesium anthracene systems for the $\ce{MgH2}$ production persisted since 1980s [1] till late 2000s, when new more efficient method with better scalability for industrial use was established. One of the recent reviews in hydrogen-storage applications [2, p. 220] compares the older two-step process of $\ce{MgH2}$ synthesis: ...


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