For each of the changes described, decide whether two or...

For each of the changes described, decide whether two or more elements formed a compound or if a compound decomposed (to form elements or other compounds). Explain your reasoning in each case. (a) After a reddish-colored metal is placed in a flame, it turns black and has a higher mass. (b) A white solid is heated in oxygen and forms two gases. The mass of the gases is the same as the masses of the solid and the oxygen.

For each of the changes described, decide whether two or more elements formed a compound or if a compound decomposed (to form elements or other compounds). Explain your reasoning in each case.
(a) After a reddish-colored metal is placed in a flame, it turns black and has a higher mass.
(b) A white solid is heated in oxygen and forms two gases. The mass of the gases is the same as the masses of the solid and the oxygen.

Key Concepts

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 is essential for analyzing both synthesis and decomposition reactions. In these examples, tracking mass changes—such as the increased mass of the metal after reacting, or the mass balance between the solid, oxygen, and the resulting gases—helps confirm that the reactions adhere to this fundamental law. It ensures that all reactants are accounted for in the products, even when a substance changes from one state or compound to another.

Synthesis Reaction

A synthesis reaction is a type of chemical reaction where two or more reactants combine to form a single product. In the context of the question, when a reddish metal reacts in a flame and turns black while increasing in mass, it indicates that the metal is combining with another element (such as oxygen) to form a new compound. This process typically involves the formation of chemical bonds and a change in physical properties, which is characteristic of synthesis reactions.

Decomposition Reaction

A decomposition reaction is a chemical process in which a compound breaks down into two or more simpler substances, which may be elements or simpler compounds. In the provided example, when a white solid is heated in oxygen and forms two gases, it suggests that the original compound is breaking apart into separate gaseous components. This type of reaction involves the breaking of chemical bonds and is fundamental in understanding how complex compounds can revert to their simpler building blocks.

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