Answer: This means to find the number of neutrons you subtract the number of protons from the mass number.
Answer:
Helium is the second element on the periodic table. It is located in period 1 and group 18 or 8A on the righthand side of the table. This group contains the noble gases, which are the most chemically inert elements on the periodic table. Each He atom has two protons and usually two neutrons and two electrons.
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Helium is the second most abundant element in the universe, but here on earth, it's rather rare. Most people guess that we extract helium from the air, but actually we dig it out of the ground. Helium can be found in certain parts of the world, notably in Texas, as a minor component in some sources of natural gas.
Answer is: at lower temperatures the reaction rate would decrease.
The lower is the temperature, the slower the reaction becomes.
The Haber process is procedure for the production of ammonia, in this process atmospheric nitrogen (N₂) is converted to ammonia (NH₃):
N₂ + 3H₂ ⇄ 2NH₃ ΔrH = -92 kJ/mol.
Because this is exothermic reaction (enthalpy is less than zero), at lower temperatures, the equilibrium is in favor of ammonia, but the reaction doesn't proceed at a detectable rate.