The normal boiling point of ammonia, NH3, is 233°C, and its...

The normal boiling point of ammonia, NH3, is 233°C, and its freezing point is 278°C. Fill in the blanks. (a) At STP (0°C, 1 atm pressure), NH3 is a ________. (b) If the temperature drops to 240°C, the ammonia will ________ and become a ________. (c) If the temperature drops further to 280°C and the molecules arrange themselves in an orderly pattern, the ammonia will ________ and become a ________. (d) If crystals of ammonia are left on the planet Mars at a temperature of 2100°C, they will gradually disappear by the process of ________ and form a ________.

Key Concepts

States of Matter

Matter exists primarily in three states—solid, liquid, and gas—each characterized by distinct particle arrangements and energy levels. In solids, particles are closely packed in an orderly structure, providing rigidity and shape. In liquids, particles are less tightly packed, allowing flow while still maintaining definite volume. Gases have widely separated, fast-moving particles, making them highly compressible and allowing them to fill any available space.

Boiling Point

The boiling point is the temperature at which a substance transitions from its liquid phase to its gaseous phase under a given pressure. At this temperature, the vapor pressure of the liquid equals the atmospheric pressure, and bubbles of vapor form within the liquid, leading to a rapid phase change.

Freezing Point

The freezing point is the temperature at which a liquid becomes a solid as its particles lose energy and settle into an organized, fixed structure. This temperature is also referred to as the melting point in reverse, marking the boundary between the liquid and solid phases.

Phase Transitions

Phase transitions are the changes in the state of matter that occur due to variations in temperature and pressure. Key transitions include the transformation from liquid to gas (vaporization) and from gas to liquid (condensation), as well as the change from liquid to solid (freezing or solidification) and the reverse (melting). Additionally, some substances can transition directly between solid and gas through sublimation and deposition.

Condensation

Condensation is the process where a gas loses heat and transitions into the liquid state. This occurs when the temperature falls sufficiently low so that the vapor pressure drops below the surrounding pressure, allowing the particles to come together to form a liquid.

Deposition

Deposition is the direct transition of a substance from the gaseous state to the solid state, bypassing the liquid phase. This process occurs under conditions where the temperature is low enough for gas molecules to arrange themselves directly into an ordered, solid structure.

Sublimation

Sublimation is the phase change in which a solid transforms directly into a gas without passing through the liquid phase. This endothermic process occurs under certain conditions of temperature and pressure when the energy supplied is sufficient to break the intermolecular bonds in the solid, allowing the particles to disperse as gas.

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