Final answer:
A crystalline solid requires the most heat energy to enter the gas phase due to the process of sublimation, which necessitates a large amount of energy to overcome the strong forces between its particles.
Step-by-step explanation:
The substance that will require the most heat energy to enter the gas phase is a crystalline solid. This is because the process to turn a solid directly into a gas is called sublimation, and it requires a significant amount of energy. Sublimation occurs when a solid transitions into a gas phase without passing through the liquid phase, demanding energy to overcome the strong intermolecular forces present in a solid. To sublimate, the energy required is given by the equation Q = mLs, where Ls is the heat of sublimation, indicating the energy necessary to change a substance from the solid to the vapor phase. Therefore, we can determine that a crystalline solid will need the most heat energy to become a gas as it undergoes sublimation.
If a substance has relatively strong intermolecular forces, a high melting point, and is not easily compressed, it will most likely be a solid.
When a substance is in the solid state, its particles are closely packed and have strong intermolecular forces holding them together. These strong forces require the most heat energy to overcome, making it more difficult for the substance to enter the gas phase.