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:

1. Claim: This is a chemical change.
2. Evidence 1: Gas bubbles are produced. The formation of a gas (carbon dioxide, in the case of effervescent tablets) is a key indicator of a chemical reaction, as new substances are being formed from the tablet's components and water.
3. Evidence 2: A temperature change occurs (the water feels colder). This shows an endothermic reaction is taking place, where energy is absorbed from the surroundings as chemical bonds break and form new ones, which is characteristic of a chemical change.
4. Reasoning: Physical changes only alter the form or state of a substance without creating new chemical identities. Here, the tablet's components react with water to form new substances (including gas), and the energy change confirms a chemical reaction has occurred, not just a physical dissolving or breaking apart of the tablet.

Answer:

This is a chemical change. The formation of gas bubbles (a new substance, carbon dioxide) and the measurable temperature drop (indicating an endothermic chemical reaction) confirm that the tablet's components have reacted with water to form new chemical substances, rather than just undergoing a physical change like dissolving.