Question

A beaker was half filled with freshly distilled H2O and placed on a hot plate. As the temperature of the water reached 100°C, vigorous bubbling was observed in the beaker. The gaseous contents of the bubbles were analyzed. The presence of which of the following substances would support the claim that the observed phenomenon was a physical change?
1-H2(g)
2-O2(g)
3-CO2(g)
4-H2O(g)

Answer 1

Answer:

4-$H_{2}O_{(g)}$

Explanation:

Initially, the beaker contains distilled water which is liquid water at room temperature. When the beaker was placed on a hot plate and heat energy was applied the temperature of the system increases gradually until the boiling point was reached. Water generally boils at 100°C and at this temperature, liquid water changes to vapor or gas. In addition, liquid water and steam or water vapor are in equilibrium. Therefore, the presence of water vapor ($H_{2}O_{(g)}$) indicates that the process is a physical change.

Answer 2

Answer:

If anything but H2O were found, it would be evidence of a chemical change. Therefore, 4 is the only viable evidence that it was a physical change of H2O liquid to H2O gas.