Difficulty: Medium

Average Score: 64%

Which scenario demonstrates a chemical change?

Rationale

A cut of meat spoils when left out.

The spoiling of meat involves complex biochemical reactions, including the growth of bacteria that break down the proteins and fats, resulting in new substances and a change in the meat's chemical composition. This transformation exemplifies a chemical change, as it leads to irreversible alterations in the material.

A (An ice cube melts into water.) YOUR ANSWER

Melting is a physical change where the state of the substance changes from solid to liquid due to heat absorption. The chemical composition of water remains unchanged throughout this process, as both ice and liquid water are composed of H2O molecules.

B (Droplets form on a cold glass cup.) YOUR ANSWER

The formation of droplets on a cold glass cup is a physical change, specifically condensation. This process involves water vapor in the air transitioning to liquid due to cooling, but the molecular structure of water remains the same, indicating no chemical change has occurred.

C (Water is boiled to water vapor.) YOUR ANSWER

Boiling water to create vapor is another example of a physical change. The water molecules remain chemically identical as they transition from liquid to gas. This phase change does not alter the molecular structure of H2O, similar to the melting of ice.

D (A cut of meat spoils when left out.) CORRECT

The spoiling of meat involves the breakdown of complex organic molecules and the production of gases and other compounds by bacteria, resulting in new chemical substances. This irreversible process constitutes a chemical change, as it fundamentally alters the meat's original properties.

Conclusion

Chemical changes involve transformations that produce new substances with different properties, as seen in the spoiling of meat. In contrast, both melting, condensation, and boiling are physical changes, preserving the original chemical identities of the substances involved. Understanding these distinctions is crucial in fields such as food safety and chemical analysis.

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