A polyatomic ion, also known as a molecular ion, is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered to be acting as a single unit. The prefix poly- means "many," in Greek, but even ions of two atoms are commonly referred to as polyatomic
The enthalpy of an intermediate step should be manipulated when used to produce an overall equation by using the Hess's law. You could multiply the enthalpy by -1 if this equation is reversed in theory.
[Co(NH₃)₅Br]²⁺
Ligands and charges on them,
5 × NH₃ = 5 × 0 = 0
1 × Br⁻¹ = 1 × -1 = -1
Charge on sphere = +2
So, putting values in equation,
Co + (0)₅ - 1 = +2
Co + 0 - 1 = +2
Co - 1 = +2
Co = +2 + 1
Co = +3
Result:
Oxidation state of Co in [Co(NH₃)₅Br]²⁺ is +3.
Explanation:
According to Le Chatelier's principle, any disturbance caused in an equilibrium reaction will shift the equilibrium in a direction that will oppose the change.
As the given reaction is as follows.

(a) When increase the temperature of the reactants or system then equilibrium will shift in forward direction where there is less temperature. It is possible for an endothermic reaction.
Thus, formation of
will increase.
- (b) When we decrease the volume (at constant temperature) of given reaction mixture then it implies that there will be increase in pressure of the system. So, equilibrium will shift in a direction where there will be decrease in composition of gaseous phase. That is, in the backward direction reaction will shift.
Hence, formation of
will decrease with decrease in volume.
- When we increase the mount of
then equilibrium will shift in the direction of decrease in concentration that is, in the forward direction.
Thus, we can conclude that formation of
will increase then.