Conservation of Mass in Chemical Reactions

The video explains the principle of conservation of mass in chemical reactions, emphasizing that mass is conserved as atoms are neither created nor destroyed, only rearranged. It illustrates this with examples, such as the reaction between sodium and chlorine, and highlights the importance of balancing chemical equations. The video also discusses exceptions in reactions involving gases, where mass may appear to change due to gases escaping or being absorbed from the air. It concludes with a summary of key points, stressing the importance of conducting experiments in sealed containers to accurately measure mass changes.

What does the conservation of mass principle state?

• Mass is always conserved in a chemical reaction.

• Atoms are created in a chemical reaction.

• Mass is always lost in a chemical reaction.

• Atoms are destroyed in a chemical reaction.

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In the reaction between sodium and chlorine to form sodium chloride, why do we need two sodium atoms on the left?

• Because chlorine atoms are larger.

• Because each chlorine molecule has two chlorine atoms.

• Because sodium is heavier than chlorine.

• Because sodium atoms are smaller.

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How do we demonstrate the conservation of mass using relative formula masses?

• By comparing the total relative formula masses of reactants and products.

• By measuring the volume of reactants and products.

• By counting the number of molecules.

• By observing the color change in the reaction.

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What is the total relative formula mass of sodium chloride formed from 2.3 grams of sodium and 3.5 grams of chlorine gas?

• 5.8 grams

• 2.3 grams

• 3.5 grams

• 6.8 grams

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Why might the mass seem to change when a gas is involved in a reaction?

• Because the gas changes color.

• Because the gas is lighter than the products.

• Because the gas is heavier than the reactants.

• Because the gas can come from the air or float off into the air.

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What happens to the mass of magnesium when it reacts with oxygen to form magnesium oxide?

• The mass decreases.

• The mass remains the same.

• The mass increases.

• The mass fluctuates.

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If we decompose calcium carbonate in a sealed container, what happens to the mass?

• The mass fluctuates.

• The mass increases.

• The mass remains the same.

• The mass decreases.

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What should be done to avoid apparent changes in mass during experiments involving gases?

• Measure the mass more frequently.

• Use a different gas.

• Conduct the experiment in a sealed container.

• Use a larger container.

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What is a likely reason for an increase in mass during a chemical reaction?

• One of the reactants is a gas.

• One of the products is a gas.

• The reactants are impure.

• The reaction is incomplete.

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What is a likely reason for a decrease in mass during a chemical reaction?

• One of the reactants is a gas.

• One of the products is a gas.

• The reaction is incomplete.

• The reactants are impure.

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NGSS.MS-PS1-5