Atoms cannot physically get more compact (temperature lowering increases the space between atoms) At absolute zero, the atoms are as physically close together as allowed by the physical laws governing it.
18. c
19. A
20. decomposition reaction
21. 4
22. 0.04%
_Mg + _HCL = _MgCl2 + H2
Separate the terms on each side:
_Mg + _HCl = _MgCl2 + H2
Mg- 1 Mg-1
H-1 H-2
Cl-1 Cl-2
Mg is balanced on both sides so move on to the next (put a 1 in the space).
1Mg
There are two H's and two Cl's on the results side, so to balance the equation put a 2 as a coefficient for HCl and it'll all balance out.
2HCl
Balamced equation will be:
1Mg + 2HCL = 1MgCl2 + H2
The correct name for the N3- ion is a nitride ion.