Can you explain the evidence for why mass is conserved during a chemical reaction using the balanced chemical equation below.

Question

Na₂SO₃ + 2 HCL = 2NaCl + H₂O + SO₂

Answer 1

Chemical reaction equations are in the unit "moles". If you wanted to, you could, with a balanced chemical reaction equation, convert to mass by using the molar mass and the associated moles and numbers of atoms and then show that the mass is equivalent on both sides of the equation. But since the mass of each element is the same on one side of the equation as the other, and since there are equivalent numbers of element atoms on each side as the other, then it seems sort of trivial to say the mass is the same. Of course it is. But, here goes:

The mass on the left side is:

Na: 2(22.990) = 45.980

S: 1(32.066) = 32.066

O: 3(15.999) = 47.997

H: 2(1.008) = 2.016

Cl: 2(35.453) = 70.906

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198.965

The mass on the right side:

Na: 2(22.990) = 45.980

Cl: 2(35.453) = 70.906

H: 2(1.008) = 2.016

O: 1(15.999) = 15.999

S: 1(32.066) = 32.066

O: 2(15.999) = 31.998

-------------------------------

198.965

Mass on the left = mass on the right. Mass is conserved.

Answer 2

The law of conservation of mass states that for any system closed to all transfers of matter, the mass of the system must remain constant over time.

For the reaction: Na₂SO₃ + 2 HCL = 2NaCl + H₂O + SO₂

The mass of reactants= 1 mole(2 x 23 + 1 x 32 + 3 x 16) g + 2 mole (1 + 35.5) g = 199 g

The mass of products = 2 mole (23 + 35.5) g + 1 mole (2 x 1 + 16) + 1 mole (32 + 2 x 16) = 199 g

The total mass after the reaction is the same as before the reaction, although the atoms are rearranged into different compounds after the reaction.