Question

Supply the term that describes each of the following changes of physical state: (a) solid to liquid (b) liquid to gas

Short answer

(a) Melting; (b) Vaporization or Boiling.

Step-by-step solution

Identify the Transition

Understand that the question is asking for the name of the process when a substance changes from one state to another.

Understanding State (a)

Recognize that when a solid turns into a liquid, the process is known as melting. This occurs when a solid gains enough energy to overcome the forces holding it together and becomes a liquid.

Understanding State (b)

Recognize that when a liquid turns into a gas, the process is known as vaporization or boiling. This occurs when a liquid gains enough energy for the molecules to escape into a gaseous state.

Key concepts

Melting

Melting is the process where a solid changes into a liquid. This occurs when the solid absorbs enough heat energy to disrupt its molecules from their fixed positions.

• Heat is applied to the solid, increasing the kinetic energy of its molecules.
• The molecules begin vibrating more vigorously and eventually have enough energy to break free from their fixed positions.
• As a result, the solid becomes a liquid.

It's important to note that during melting, the temperature remains constant, known as the melting point, until the entire solid has transitioned into a liquid. This is because the energy absorbed is used to break intermolecular forces rather than increasing temperature.

Vaporization

Vaporization is the process of a liquid turning into a gas. This can happen in two primary ways: boiling and evaporation.

• Boiling: Boiling occurs when a liquid is heated to its boiling point, at which molecules throughout the liquid gain enough energy to form bubbles of gas that rise to the surface.
• Evaporation: Evaporation can occur at temperatures below boiling point and happens only at the surface of the liquid, where molecules gain enough energy to transition to gas.

During vaporization, like during melting, the temperature of the liquid remains constant while it changes state, as the energy is consumed in overcoming intermolecular forces.

States of Matter

States of matter refer to the distinct forms that different phases of matter take on, with the most familiar being solid, liquid, and gas.

• Solids: Have definite shape and volume due to closely packed molecules that are fixed in place.
• Liquids: Have a definite volume but take the shape of their container. Molecules are close together but move more freely than in a solid.
• Gases: Have neither definite shape nor volume; their molecules move freely and rapidly, allowing them to expand to fill their container.

Under certain conditions, matter can also exist in more exotic states, like plasma and Bose-Einstein condensates. Each state is characterized by distinct physical properties determined by the energy and arrangement of the molecules.