Question

1. a student places a piece of zinc metal into a beaker of hydrochloric acid and records the following observations:

observation	evidence collected
2	the beaker becomes warmer over time
3	the metal gradually disappears
4	the liquid looks the same as before, just with fewer bubbles

based on the data, which students conclusion is best supported by the students observations?
a physical change occurred because the appearance of the liquid did not change.
a chemical change occurred because zinc mixed evenly into the hydrochloric acid without forming anything new.
a chemical change occurred because new substances formed and there was a change in thermal energy.
a physical change occurred because the zinc only changed size and shape.

Explanation:

Step1: Recall chemical and physical change definitions

A chemical change results in new substances being formed and often involves energy - changes. A physical change only alters physical properties like state, shape etc. without forming new substances.

Step2: Analyze the observations

Bubbles forming means a gas is produced, the beaker getting warmer indicates a heat - change (energy change), and the metal disappearing means new substances are formed as the zinc reacts with hydrochloric acid.

Step3: Evaluate the options

The first option is wrong as there are new substances formed and energy changes. The second option is wrong as new substances are formed. The third option is correct as new substances are formed (gas and a zinc - chloride solution) and there is a change in thermal energy. The fourth option is wrong as it is a chemical change not a physical change.

Answer:

A chemical change occurred because new substances formed and there was a change in thermal energy.