Justify Whether Reaction Occurred Practice Test

A student adds 5.0 g of table salt (NaCl) to 100 mL of water in a beaker and stirs for 2 minutes.

Observations/data:

• Salt crystals disappear; the liquid remains clear.
• Temperature changes from 21.0°C to 19.8°C.
• No bubbling, no odor, and no solid forms later.
• The student evaporates the water overnight and recovers white crystals that look like the original salt.

Based on the evidence, did a chemical reaction occur? Choose the best CER-style justification.

A student conducts two trials.

Trial 1: 3.0 g of sugar is stirred into 50 mL of water. The sugar disappears, the solution stays clear, and the temperature changes from 21.0°C to 20.2°C.

Trial 2: 3.0 g of sugar is heated strongly in a dry test tube. The sugar turns brown, then black, and a noticeable burnt smell appears. A dark solid remains stuck to the tube.

For Trial 2, did a chemical reaction occur? Choose the best CER justification.