Three samples of a solid substance composed of elements A and Z were prepared. The first contained 4.31 g A and 7.70 g Z. The second sample was 35.9% A and 64.1% Z. It was observed that 0.718 g A reacted with Z to form 2.00 g of the third sample. Show that these data illustrate the law of definite composition.

The percentage composition of the elements of the compound in the three samples is the same.

Explanation:

The law of definite proportions states that all pure samples of a particular chemical compound contain the same elements in the same proportion by mass.

Sample A:

Mass of A = 4.31 g; mass of Z = 7.70 g

Total mass of sample = 12.01

Percentage mass of A in the sample = (4.31 * 100)/12.01 = 35.9 %

Percentage mass of Z in the sample = (7.70 * 100)/12.01 = 64.1 %

Sample B:

Percentage mass of A in the sample = 35.9 %

Percentage mass of Z in the sample = 64.1 %

Sample C:

Mass of A = 0.718 g; Total mass of sample = 2.00 g

mass of Z = mass of sample - mass of A = 2.00 g - 0.718 g = 1.282 g

Percentage mass of A in the sample = (0.718 * 100)/2.00 = 35.9 %

Percentage mass of Z in the sample = (1.282 * 100)/2.00 = 64.1 %

From the calculations, it can be seen that the percentage composition of the elements in the compound is the same for the three samples.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.