Bell Ringer 3-8-24

Which one of the following is the correct statement of Law of Conservation of Mass?

• There is a change in mass when a chemical reaction takes place.

• In a reaction, the total mass of the reactant is always greater than the total mass of the products.

• Atoms combine in a fixed ratio to form compounds.

• Mass can neither be created nor destroyed.

Answer explanation

The correct statement of Law of Conservation of Mass is that mass can neither be created nor destroyed.

What happens to the total mass of the substances after a chemical reaction?

• It decreases.

• It increases.

•  It remains the same.

• It increases then decreases.

In a chemical reaction, iron reacts with chlorine gas to form ferric chloride. If the Law of Conservation of Mass is correct, what is the number of Fe and Cl atoms at the beginning of the reaction?

2Fe ( s ) + 3 Cl ₂ ( g ) → 2 FeCl ₃ ( s )

• Fe=3, Cl=4

• Fe=1, Cl=2

• Fe=2, Cl=6

• Fe=2, Cl=3

Answer explanation

The balanced equation shows that 2 Fe atoms react with 3 Cl2 molecules, resulting in 2 FeCl3 molecules. Therefore, at the beginning of the reaction, there are 2 Fe atoms and 6 Cl atoms.

Which one of the following combinations can a student select to prove the Law of Conservation of Mass? (Hint: The reactants in the lab in the correct phase of matter)

• BaCl₂(aq) + Na₂SO₄ (s)

• Na₂SO₄ (s) + BaCl₂ (s)

• BaCl₂(aq) + Na₂SO₄ (aq)

• Na₂SO₄(aq) + BaCl₂ (s)

What is the result of the following chemical reaction in terms of mass conservation?

2H₂(g) + O₂(g) → 2H₂O(l)

• The mass of the products is less than the mass of the reactants.

• The mass of the products is greater than the mass of the reactants.

• The mass of the products is equal to the mass of the reactants.

• The reaction does not follow the Law of Conservation of Mass.

If reaction starts with 20g of reactants it should produce 

• a total of 40g of products
• a total of 10g of products
• a total of 80 g of products
• a total of 20g of products

The following chemical reaction occurs:

NaHCO₃(aq) + CH₃COOH(aq)→ CH₃COONa(aq)+ H₂CO₃(aq)

sodium bicarbonate + acetic acid --> sodium acetate + carbonic acid

However, carbonic acid is highly unstable and will decompose to produce water and carbon dioxide H₂CO₃(aq)⇌H₂O(l)+CO₂(g)↑. The carbon dioxide will actually bubble out of solution and be lost.

What product will be lost in this reaction?

• elimination of CO₂ gas

• elimination of O₂ gas

• elimination of H₂O liquid

While verifying the Law of Conservation of Mass, a student added 5 g of sodium bicarbonate to a test tube containing 14.5 g acetic acid. The total mass of the reactants is 19.5 g. But the mass of the product after the reaction is only 16.2 g. The reduction in the mass of the product is due to elimination of CO₂ after breaking down carbonic acid is highly unstable and will decompose to produce water and carbon dioxide H₂CO₃(aq)⇌H₂O(l)+CO₂(g)↑. How much product is lost in this reaction?

• elimination of 16.2 g CO₂

• elimination of 14.5 g CO₂ gas

• elimination of 3.3 g CO₂ gas

Jin bought a heat pack that weighs 15 g. He shook it so it would release heat to warm his hands. The release of heat indicates a chemical reaction took place in a closed system. What would be the mass of the heat pack after the chemical reaction?

• 5 g

• 10 g

• 12 g

• 15 g

In a chemical reaction, one molecule of nitrogen reacts with three molecules of hydrogen to form ammonia. If the Law of Conservation of Mass is correct, what will be the number of atoms of nitrogen and hydrogen at the end of the reaction?

N₂ + 3H₂ ---> 2NH₃

• N=2, H=6

• N=1, H=3

• N=6, H=2

• N=3, H=3

Answer explanation

The balanced chemical equation shows that 1 molecule of N reacts with 3 molecules of H to form 2 molecules of NH3. Therefore, at the end of the reaction, N=2 and H=6 according to the Law of Conservation of Mass.