Question

Indicate whether the following changes of physical state require heating or cooling: (a) liquid to solid (b) liquid to gas

Short answer

(a) Cooling, (b) Heating.

Step-by-step solution

Identify Change of State for Liquid to Solid

The physical change of state where a substance transitions from a liquid to a solid is called freezing. During freezing, the temperature of the substance decreases until it reaches its freezing point.

Determine Energy Requirements for Freezing

Freezing is a process that involves the removal of heat energy from the liquid. As energy is removed, the particles lose kinetic energy and start to arrange themselves into a solid structure. Thus, freezing requires cooling.

Identify Change of State for Liquid to Gas

The physical change of state where a substance transitions from a liquid to a gas is called vaporization, which includes both evaporation and boiling. During vaporization, the temperature of the substance increases until it reaches its boiling point.

Determine Energy Requirements for Vaporization

Vaporization is a process that requires the addition of heat energy to the liquid. As energy is added, the particles gain kinetic energy and escape the liquid phase to become gas. Thus, vaporization requires heating.

Key concepts

Freezing

Freezing is an intriguing process where a substance transitions from liquid to solid. This change in state occurs when the temperature of the liquid drops to its freezing point. At this point, the forces between particles become strong enough to hold them in a fixed position, creating a solid.

For freezing to happen, heat energy must be removed from the liquid. This removal of heat decreases the particles' kinetic energy, allowing them to slow down and settle into a more ordered structure. Key points to remember about freezing include:

• Occurs at the freezing point of the substance.


• Involves the removal of energy.


• Results in a more ordered, solid state.

This process is common in everyday occurrences, like water turning into ice, and is essential for many natural and human-made processes.

Vaporization

Vaporization is the process where a liquid turns into a gas, and it can occur in two different ways: evaporation and boiling. Both processes involve the liquid reaching a point where its molecules have enough energy to break free from the surface and become gas.

Evaporation usually occurs at the surface of a liquid at temperatures below the boiling point, while boiling happens throughout the liquid once it reaches its boiling point. Understanding the nuances of vaporization involves remembering these points:

• Requires addition of heat energy.


• Can occur slowly (evaporation) or rapidly (boiling).


• Increases the kinetic energy of the particles.

Vaporization is vital in various applications, such as cooling mechanisms, where the process absorbs large amounts of heat, helping to maintain temperature.

Energy Requirements

The energy requirements for phase changes are crucial for understanding how substances move between states. Each phase change, whether freezing or vaporization, necessitates a specific energy shift—either adding or removing energy.

**For Freezing:**
- Requires removal of heat energy.
- Decreases kinetic energy of particles, leading to a solid state.

**For Vaporization:**
- Requires addition of heat energy.
- Increases kinetic energy of particles, allowing them to form a gas.
Understanding these requirements is essential in fields like thermodynamics and material science. They help explain phenomena such as why ice is used to cool drinks and how steam is generated. These energy dynamics are fundamental to both nature and technology, affecting climate, energy generation, and industrial processes.