# Video: Identifying the Name of the Transition of a Substance from Solid to Gas without Going through the Liquid Phase in a Set of Names

Which of the following is the transition of a substance directly from the solid to the gas phase without going through the liquid phase? [A] Sublimation [B] Condensation [C] Critical point [D] Deposition [E] Triple point

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### Video Transcript

Which of the following is the transition of a substance directly from the solid to the gas phase without going through the liquid phase? (A) Sublimation, (B) condensation, (C) critical point, (D) deposition, or (E) triple point.

All substances can potentially exist as solids, liquids, or gases, depending on the conditions that they are under, such as temperature and pressure. When a solid changes to a liquid, this is called melting. The opposite process, when a liquid changes to a solid, is called freezing or solidification. These two processes occur at the same temperature called the melting point, or sometimes the freezing point.

When a liquid changes to a gas, this process is called boiling. Note that the boiling temperature of a substance depends on the air pressure. Also, boiling is not the same as evaporation. Even though evaporation is the change from a liquid to a gas, evaporation can occur at many temperatures. However, boiling occurs at one specific temperature unique to that substance and is dependent on the air pressure.

The change in state from a gas to a liquid is known as condensation, or sometimes liquification. The temperature at which boiling and condensation occur is called the boiling point, and occasionally called the condensation point. Melting, freezing, boiling, and condensation are very common processes for many substances.

The change in state from a solid to a gas or a gas to a solid directly without any liquid middle phase is unusual. However, it can occur if conditions are right, such as air pressure. The change of a solid directly to a gas is called sublimation. The opposite process, gas changing directly to a solid, is called deposition. So, we have seen that sublimation is the change directly from a solid to a gas. Condensation is the change from a gas to a liquid. And deposition, the change from a gas to a solid.

Critical point does not describe a state change but is rather the specific temperature and pressure at which a liquid and vapor of a substance can coexist. It is the specific temperature and pressure at which the density of a liquid and its vapor are the same. And so, the two phases are indistinguishable. Triple point is very similar. Triple point is also not the change of state or the process of a change of state. Triple point is a specific temperature and pressure at which the three phases, solid, liquid, and vapor, for a substance coexist at the same time.

The question asks, which of the following is the transition of a substance occurring from the solid to the gas? Transition means the change in state. So, we can rule out option (C), critical point, and option (E), triple point, because they are not changes but specific temperature and pressure values. We have seen that the transition or change in state of a substance directly from the solid to gas phase without going through the liquid phase is called sublimation. So, the answer is option (A), sublimation.