Question

6-10 Identify X (chemical symbol and mass number) in each of the following 10 pts reactions: (a) X +4 N → H+? O (b) {Li + H – He + x

Answer 1

For solving these chemical reactions, follow conservation law and can be balanced in two ways,

1. The sum of the mass numbers of the reactants equals to the sum of the mass numbers of the product.

2. The sum of the charges of the reactants equals the sum of the charges of the products.

Hence in the reaction,

$(a)X+_{7}^{14}\textrm{N}\rightarrow _{1}^{1}\textrm{H}+_{8}^{17}\textrm{O}$

If you add the mass numbers (top) of the products, it gives a sum of 18 (1+17). So the sum of mass numbers of reactants must also be 18. Since mass number of nitrogen is given as 14, the mass number of X will be 18 - 14 = 4.

Similarly, if you add the atomic numbers (bottom) of the products, it gives a sum of 9 (1+8). So the sum of atomic numbers of reactants must also be 9. Since atomic number of nitrogen is given as 7, the mass number of X will be 9 - 7 = 2.

Hence X can be written as,

$_{2}^{4}\textrm{X}$

From periodic table , it is clear that the element with atomic number 2 and mass number 4 is hydrogen. Hence the X represented as actual element is,

$X\ is\ _{2}^{4}\textrm{He}$

Similarly, in the reaction,

$(b)_{3}^{7}\textrm{Li}+_{1}^{1}\textrm{H}\rightarrow _{2}^{4}\textrm{He}+X$

If you add the mass numbers (top) of the reactants, it gives a sum of 8 (7+1). So the sum of mass numbers of products must also be 8. Since mass number of Helium is given as 4, the mass number of X will be 8 - 4 = 4.

Similarly, if you add the atomic numbers (bottom) of the reactants, it gives a sum of 4 (3+1). So the sum of atomic numbers of products must also be 4. Since atomic number of Helium is given as 2, the mass number of X will be 4 - 2 = 2.

Hence X can be written as,

$_{2}^{4}\textrm{X}$

From periodic table , it is clear that the element with atomic number 2 and mass number 4 is hydrogen. Hence the X represented as actual element is,

$X\ is\ _{2}^{4}\textrm{He}$