2. When liquid gasoline is burned, the oxygen in the air combined with the octane in the gasoline produces gaseous carbon dioxide and water vapor. Which statement about this reaction is correct?
Answer: A
The total mass of the products is equal to the total mass of the reactants.
In a chemical reaction, such as the combustion of gasoline, the law of conservation of mass states that the total mass of the reactants must equal the total mass of the products. Therefore, when liquid gasoline is burned, the mass is conserved throughout the reaction.
A) The total mass of the products is equal to the total mass of the reactants.
This statement is correct as it aligns with the law of conservation of mass. During the combustion of gasoline, although the reactants (gasoline and oxygen) are transformed into products (carbon dioxide and water vapor), the total mass remains unchanged, confirming that mass is conserved in the reaction.
B) The total amount of energy slightly decreases during the reaction.
This statement is incorrect. While energy is released in the form of heat during the combustion of gasoline, the total energy is conserved according to the first law of thermodynamics. Energy may change forms (from chemical potential to thermal), but it does not decrease overall.
C) The molecules remain the same, but the state of matter changes.
This statement is incorrect. In the combustion of gasoline, the molecules of the reactants (octane and oxygen) are transformed into different molecules (carbon dioxide and water vapor). Therefore, the identity of the molecules changes, not just their state of matter.
D) The volume of the reactants is equal to the volume of the products.
This statement is also incorrect. While the number of gas molecules may change during the reaction (since gases can occupy different volumes), the total volume of the reactants does not equal the total volume of the products due to the differences in gas behavior and the formation of new gaseous products.
Conclusion
The correct answer, A, accurately reflects the principle of conservation of mass, which is fundamental to all chemical reactions. The other options fail to capture this key concept, as they either misrepresent energy conservation, misinterpret molecular identity, or incorrectly discuss volume relationships in the reaction.