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Index (H)
HA - HC
HD - HF
HG - HJ
HK - HN
HO - HR
HS - HV
HW - HZ
Moment of truth
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The Sun, with a diameter of 1,392,000 km, is made of 94% hydrogen atoms. |
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hydrated lime Chem.
See slaked lime.
hydrocarbon Chem.
A chemical compound that contains only carbon and hydrogen. There are a large number of hydrocarbons. The main examples are the alkanes (CnH2n+1), alkenes (CnH2n) and
alkynes (CnH2n-1). These compounds are linear hydrocarbon chains. Hydrocarbons can also form cyclic compound such as arenes and cycloalkanes (CnH2n).
hydrogen burning Astron.
A thermonuclear process that occurs in the core of a star, such as the Sun. It is believed to occur via the following proton-proton chain reactions:
where e+ is the positron, ne is the electron neutrino. The energy release for each 24He (helium) nucleus is about 26 MeV. The temperature must reach at least 106 K for the
reaction to occur. It is essentially a fusion reaction that involves 4 protons (p) to produce one 24He nuclei (alpha particle).
hydrolysis Chem.
A chemical reaction of a compound with water. For example, hydrolysis normally occur for salts of weak acids or bases. For instance, the salt of ethanoic acid (acetic acid), sodium ethanoate, reacts with water to give the acid:
hypertonic solution Biol.
A solution that has a higher osmotic pressure than the other solution. In other words, a hypertonic solution has a greater solute concentration than the other solutions. When an animal cell is placed in a hypertonic
solution (say 10% salt solution), the osmotic gradient necessitate the water to be drawn from the cell to the surrounding salt solution. Subsequently, the cell shrinks (crenated).
hypha Bot.
The plural is hyphae.
(1) A filament or thread-like structure, usually white in color, composing the mycelium of a fungus. It is usually begun to grow from a spore of a fungus.
(2) Filamentous outgrowths and branching produced by certain group of bacteria, such as Actinomycetes that give soil its freah 'earthy' smell.
hypotonic solution Biol.
A solution that has a lower osmotic pressure than the other solution. In other words, a hypotonic solution contains less solutes than the other solutions and when an animal cell is placed
in a hypotonic solution (distilled water, for example), the osmotic gradient draws water into the cell and subsequently it expands and bursts (lysed).
HW - HZ
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