Question

Which of the following statements about vaporization and steam is MOST accurate?

A. Steam produced in the upper layer of hot smoke and fire gases may cause the upper layer to expand downward.
B. Steam produced on contact with hot surfaces is more likely to result in complete vaporization of the fire stream.
C. Steam produced in the upper layer of hot smoke and fire gases will cause the upper layer to contract toward the ceiling.
D. Steam produced on contact with hot surfaces has little effect on the total volume of the upper layer of hot smoke and fire gases.

Answer 1

The most accurate statement is that steam produced in the upper layer of hot smoke and fire gases can cause the layer to expand downward. Thus, correct option is A.

Step-by-step explanation:

The statement about vaporization and steam that is MOST accurate is A: "Steam produced in the upper layer of hot smoke and fire gases may cause the upper layer to expand downward." During vaporization, heat is transferred to a substance, which then changes from liquid to gas. As water vaporizes to steam, it expands and can cause an upward expansion of the hot layer. This can result in the layer pushing downward as it expands.

Contrastingly, condensation is the reverse process where gas transforms back into liquid, and in this state, it might contract and result in a movement towards the ceiling.

For instance, when water boils in an open container, the produced steam is mixed with air, which means there is less likelihood of water molecules condensing. Hence, the liquid continues to vaporize.

Furthermore, at temperatures below boiling, such as room temperature, evaporation and condensation can still occur. The vapor pressure of water causes some liquid molecules to escape into the gas phase, and when these gas molecules lose energy, they can condense back into the liquid phase. This equilibrium maintains a consistent temperature, as seen when ice in a cup of water stays at 0 °C even on a hot day.