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Ch.20 - Nuclear Chemistry
Chapter 20, Problem 75

In an endothermic chemical reaction, do the products have more mass, less mass, or the same mass as the reactants? Explain.

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Understand the Law of Conservation of Mass: This law states that mass is neither created nor destroyed in a chemical reaction. It's important to remember this foundational principle when analyzing any chemical reaction, including endothermic reactions.
Define an endothermic reaction: An endothermic reaction is one where heat is absorbed from the surroundings. This means that the system gains energy from its environment, typically in the form of heat.
Relate energy change to mass change: According to Einstein's equation, E=mc^2, energy and mass are related. However, the amount of energy typically involved in chemical reactions is so small that the corresponding mass change is negligible and not detectable with ordinary measuring equipment.
Apply the Law of Conservation of Mass to the endothermic reaction: Since the law states that mass is conserved, and the typical energy changes in chemical reactions do not significantly affect mass, the total mass of the reactants and the total mass of the products in an endothermic reaction are equal.
Conclusion: In an endothermic reaction, the products have the same mass as the reactants. The absorption of energy does not affect the total mass, adhering to the Law of Conservation of Mass.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Law of Conservation of Mass

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. This principle implies that the total mass of the reactants must equal the total mass of the products, regardless of whether the reaction is endothermic or exothermic.
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Endothermic Reactions

Endothermic reactions are processes that absorb energy, usually in the form of heat, from their surroundings. This energy absorption can lead to a temperature drop in the environment, but it does not affect the mass of the reactants and products involved in the reaction.
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Chemical Reaction Products

In a chemical reaction, the products are the substances formed as a result of the reaction between the reactants. In the context of the question, the mass of the products will be equal to the mass of the reactants, as dictated by the Law of Conservation of Mass, regardless of the energy changes involved.
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