As the gas is heated, the particles will begin to move faster. Likewise if you start to cool a gas, the particles will move slower. Because the gas remains at a constant pressure and volume, the particles cannot spread out so they simply move around the container even faster.
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When HCl is added to a saturated solution of PbCl2, the solubility of PbCl2 would decrease so precipitation would occur. The decrease in the solubility is due to the common ion effect or the presence of Cl- ions in both compounds.
Well, if you look at group 1 of the periodic table, you will notice a thrend. All elements in group 1 have 1 valence / outer electron. Then you look at period 2, 3, 4 and so on, you will see that the group number corresponds the number of valence/ outershell electrons. Hence, the group determines the electron(s) on the outershell.
