Question

a student places a clear, effervescent tablet (like alka - seltzer) into a beaker of room - temperature water. immediately, bubbles begin to form and rise to the surface. after two minutes, the tablet has disappeared, and the water feels slightly colder to the touch than it did before. write a claim if this is a physical or a chemical change. support your choice with evidence and reasoning.

Explanation:

A chemical change produces new substances, while a physical change only alters the form of a substance without creating new matter. The formation of bubbles (gas production) is a key sign of a chemical reaction, as the effervescent tablet's components react with water to produce carbon dioxide gas. Additionally, the temperature drop indicates an endothermic chemical reaction where energy is absorbed from the surroundings (the water). The tablet disappearing alone could be a physical dissolution, but the gas formation and temperature change confirm a chemical change occurred, creating new substances.

Answer:

This is a chemical change.

• Claim: The reaction of the effervescent tablet with water is a chemical change.
• Evidence: Bubbles (gas) are produced, and the water temperature decreases.
• Reasoning: Gas formation is a definitive indicator of a chemical reaction, as new substances (carbon dioxide gas, dissolved reaction products) are formed. The temperature drop shows the reaction absorbs energy, which is characteristic of a chemical process, not just physical dissolution.