Modeling Conservation of Mass

Does this chemical equation follow the Law of Conservation of Mass? Use evidence from the equation to support your response.

H₂ + O₂ → H₂O

Answer explanation

This equation does NOT follow the Law of Conservation of Mass.

It does not follow the law of conservation of mass because it is not balanced. There are 2 hydrogen atoms on the reactant side and 2 hydrogen atoms on the product side. There are 2 oxygen atoms on the reactant side but only 1 oxygen atom on the product side.

Since there is not the same number of oxygen atoms on both sides, the equation is not balanced. The law of conservation of mass states that mass cannot be created or destroyed. In order to follow this law, the equation needs to have the same number of each element on both sides of the equation.

Tags

NGSS.MS-PS1-5

How many total atoms of chlorine are there in 2NaCl₂?

• 1

• 2

• 3

• 4

Answer explanation

The coefficient in front Na applies to both Na and Cl. (2 x 2 = 4)

Tags

NGSS.MS-PS1-1

Which equation supports this model?

• 2H₂ + O₂ → 2H₂O

• H₂ + O₂ → 2H₂O

• 2H₂O₂ → 2H₂O

• 2H₂ + O₂ → H₂O

Answer explanation

Look at the model. There are 2 molecules of H₂ and 1 molecules of O₂ on the reactant side. On the product side, you have 2 molecules of H₂O.

Tags

NGSS.MS-PS1-5

NGSS.MS-PS1-2

Balance this equation:

Al + O₂ → Al₂O₃

• 2Al + O₂ → Al₂O₃

• 4Al + O₂ → 2Al₂O₃

• 4Al + 3O₂ → 2Al₂O₃

• 2Al + 2O₂ → 4Al₂O₃

Tags

NGSS.MS-PS1-5

Balance this equation and then calculate the total atomic mass of the reactants and products.

H₂ + O₂ → H₂O

Answer explanation

Balanced equation: 2H₂ + O₂ → 2H₂O

Reactants:

H = 4 atoms x 1 = 4

O = 2 atoms x 16 = 32

Total mass: 36 amu

Products:

H = 4 atoms x 1 = 4

O = 2 x 16 = 32

Total mass: 36 amu

Tags

NGSS.MS-PS1-5

Which number represent a coefficient in this equation?

Cl₆ + Na₆ → 3Cl₂Na₂

• 2

• 3

• 6

• 8

Answer explanation

Coefficient is the number in front of the substance. It tells you how many molecules (or groups) of the substance you have.

Tags

NGSS.MS-PS1-5

How many atoms of oxygen are on each side of the chemical equation?

4FeS + 7O₂ → 2Fe₂O₃ + 4SO₂

Answer explanation

Reactant side: 7 x 2 = 14 atoms

Product side: (2 x 3) + (4 x 2) = 14 atoms

Tags

NGSS.MS-PS1-5

Does this reaction follow the Law of Conservation of Mass? Explain.

Answer explanation

Yes, this reaction does follow the law of conservation of mass. The mass of the reactants were 300.23g. After the substances were mixed, the mass of the products were 300.23g. The Law of Conservation of Mass states that matter cannot be created or destroyed. Since the mass of the reactants and products are the same, this proves that no matter was created or destroyed during this reaction.

Tags

NGSS.MS-PS1-5

NGSS.MS-PS1-2

Jackie and Josh wanted to do an experiment to demonstrate the Law of Conservation of Mass. To do this, they measured the mass of baking soda and vinegar (reactants) and received a mass of 35g. Then, they mixed the two substances and after the reaction, the mass was measured at 33g. What is the possible explanation as to why the mass was not the same before and after the reaction?

• Mass was destroyed in the reaction.

• They did not measure correctly.

• The students did not include an instrument to capture the gas produced in the reaction.

• These two substances do not react so nothing would have happened.

Answer explanation

This reaction needs to be completed in a "closed" system; otherwise, the gas produced will escape, leaving the products to have less mass than the reactants.

Tags

NGSS.MS-PS1-5

NGSS.MS-PS1-2

The number written below and to the right of a chemical symbol that shows the number of atoms present in that element is called the (a)   .