The question requires us to explain why the number 2 is assigned to both K and Cl in the two different reactions given.
The chemical equations provided refer to the formation of the compounds potassium oxide (K2O) and calcium chloride (CaCl2) from their respective ions.
To form potasisum oxide, ions K+ (with oxidation number +1) react with ions O2- (with oxidation number -2). The amount of K and O in the molecule refers to the formation of a neutral ionic compound, where the charges of the ions together must reach 0 (neutral charge). In this case, since K ion has charge +1 and O ion has charge -2, we would need 2 K+ to combine with 1 O2- ion. The net charge is: (2 * (+1)) + (1 * (-2) = 0
The reaction to form potassium oxide must contain the appropriate amount of K+ and O2- to produce 1 mol of K2O:
Now, considering the formation of calcium chloride and the charges of ions Ca2+ and Cl- (Ca forms a cation with charge +2 and Cl forms an anion with charge -1), the neutral compound must contain 2 atoms of Cl and 1 atom of Ca. The net charge would be: (2 * (-1)) + (1 * (+2)) = 0
The reaction from Ca2+ and Cl- ions to form CaCl2 also must contain the appropriate amount of ions to form 1 mol of the compound:
In summary, the amount of each atom in the ionic compound (the subscrit numbers after the element) depends on the charge of the ions formed by this element: we must find the amount of atoms in a way that the net charge of the molecule is zero (for neutral molecules). On the other hand, when writing the chemical equation to represent the formation of the ionic compound, the reactants side (left side) must present the appropriate amount of each element in order to form the compound (the coefficients of the equation).