# How is Energy Related to the Change of State Represented by the Model?

## Introduction

Matter can exist in different states, such as solid, liquid and gas. These states have different properties and behaviors, depending on the arrangement and movement of the particles that make up the matter. A change of state is a physical change in a matter. They are reversible changes and do not involve any changes in the chemical makeup of the matter. Common changes of state include melting, freezing, sublimation, deposition, condensation, and vaporization. These changes are shown in the figure given below.

In this article, we will explore how energy is related to the change of state represented by the model. We will also look at some examples of state diagrams that show the possible states of an object and the transitions that cause a change in state.

## Energy and Change of State

Energy is the ability to do work or cause change. Energy can be transferred from one object to another, or converted from one form to another. For example, when we heat a solid, we transfer thermal energy (heat) from the heat source to the solid. This thermal energy causes the particles in the solid to vibrate faster and move further apart, weakening the forces of attraction between them. When the thermal energy is enough to overcome these forces, the solid melts and becomes a liquid. This process is called melting.

Melting is an example of an endothermic process, where heat is absorbed during the change of state. The amount of heat required to melt a unit mass of a substance at its melting point is called the latent heat of fusion. Different substances have different latent heats of fusion, depending on the strength of the forces between their particles. The stronger the forces, the more heat is required to melt them.

Similarly, when we heat a liquid, we transfer thermal energy from the heat source to the liquid. This thermal energy causes the particles in the liquid to move faster and further apart, weakening the forces of attraction between them. When the thermal energy is enough to overcome these forces, the liquid boils and becomes a gas. This process is called boiling.

Boiling is another example of an endothermic process, where heat is absorbed during the change of state. The amount of heat required to boil a unit mass of a substance at its boiling point is called the latent heat of vaporization. Different substances have different latent heats of vaporization, depending on the strength of the forces between their particles. The stronger the forces, the more heat is required to boil them.

On the other hand, when we cool a gas, we transfer thermal energy from the gas to the surroundings. This thermal energy causes the particles in the gas to move slower and closer together, strengthening the forces of attraction between them. When these forces are strong enough to hold them together, the gas condenses and becomes a liquid. This process is called condensation.

Condensation is an example of an exothermic process, where heat is released during the change of state. The amount of heat released when a unit mass of a substance condenses at its condensation point is equal to its latent heat of vaporization.

Similarly, when we cool a liquid, we transfer thermal energy from the liquid to

the surroundings. This thermal energy causes the particles in the liquid to move slower and closer together, strengthening the forces of attraction between them. When these forces are strong enough to lock them into fixed positions, the liquid freezes and becomes a solid. This process is called freezing.

Freezing is another example of an exothermic process, where heat is released during

the change of state. The amount of heat released when a unit mass of a substance freezes at its freezing point is equal to its latent heat of fusion.

Some substances can change directly from solid to gas, or from gas to solid,

without becoming a liquid in between. This is called sublimation or deposition,

depending on whether it is endothermic or exothermic.

State Diagrams

A state diagram is a graphical representation that shows how an object can change

its state in response to certain events or conditions. A state diagram consists

of states and transitions.

A state is a condition or situation that an object can be in at any given time.

A state can have certain properties or behaviors associated with it. For example,

a solid has a fixed shape and volume, while a liquid has a fixed volume but can

flow and take the shape of its container.

A transition is a change from one state to another due to some event or condition.

A transition can have certain actions or effects associated with it. For example,

when a solid melts into a liquid due to heating, it absorbs heat and changes its

shape.

Graphically, a state is rendered as a rectangle with rounded corners. A transition

is rendered as a solid directed line. The name of the event or condition that

triggers the transition is written above or beside the line. The name of the action

or effect that results from the transition is written below or beside the line.

The following state diagram shows the possible states and transitions for water.

![State diagram for water](https://www.bbc.co.uk/bitesize/guides/zwsdgdm/revision/2/state-diagram-for-water.png)

The following state diagram shows the possible states and transitions for an incident.