Arinah Khatiwada

Given,

No. of atoms of an element = 2 x 10²¹
Mass of atoms of an element = 0.4g

According to the questions,

2 x 10²¹ atoms of an element has mass 0.4g
6.022 x 1023 atoms of element has mass = 120.44g

i.e. 1 mole of atom of an element has mass 120.44g

Hence, the mass of 0.5 mole of an elements is 0.5 x 120.44g = 60.22g

In 1803, John Dalton proposed the law of multiple proportion. Law of multiple proportion states that, "When two elements which combine to form two or more different compounds, then the weight of one of the elements which combine with the constant weight of the other bear simple whole number ratio."

The law of conservation of mass is known as indestructibility of matter because there is no loss of mass when reactant reacts to form product i.e. total mass of the reactant is equal to total mass of the product.

C + 2H₂ CH₄

Total weight of reactant = 16g
Total weight of product = 16g
Total weight of reactant = total weight of product

So these data show the law of conservation of mass.

Statement:

Total sum of mass and energy of system remains constant, but they can be interconverted.

When two different elements combine separately with the fixed weight of the elements, the ratio in which they do so will be the same or some simple multiple of the ratio which they combine together.

Under similar condition of temperature and pressure, gaseous reactants and products combine in a simple whole number ratio of their volumes.