Phase changes, like melting, boiling, and condensing, are great examples of how energy works in our world.

When something changes from solid to liquid, like ice melting, it takes in heat energy. This heat energy messes up the neat arrangement of tiny particles, which causes the solid to turn into a liquid.

There’s a term called enthalpy, written as $ΔH$, that helps us understand this heat change during the phase change.

Examples of Phase Changes:

1. Melting (Solid to Liquid): When ice melts at 0°C (32°F), it takes in heat but doesn’t get hotter right away.
2. Boiling (Liquid to Gas): Water boils at 100°C (212°F), and it needs a lot of energy to do this. We call this energy the heat of vaporization.

Key Energy Principles:

• First Law of Thermodynamics: This law says energy can’t just appear or disappear; it only changes from one form to another. When ice melts or water boils, thermal energy is turned into potential energy.

• Second Law of Thermodynamics: This law tells us that disorder, or entropy, increases during these changes. As solids turn into liquids or gases, the arrangement of molecules becomes more chaotic.

Knowing these concepts helps us understand how energy changes happen in different chemical reactions. It highlights the connection between matter and energy in the study of thermodynamics.