The atoms or molecules that make up substances are always vibrating as a result of thermal energy. When a substance is hotter, that means its atoms or molecules are vibrating faster. Thermal energy always moves from a hotter area to a colder area. Adding or removing thermal energy can cause a substance to change from one state to another, and chemical reactions can cause thermal energy to increase or decrease.
To better understand thermal energy…
LET’S BREAK IT DOWN!
What is thermal energy?
All matter is made up of particles, either atoms or molecules, and these particles are constantly vibrating. The energy of these moving particles is called thermal energy and is related to the temperature of the substance. Temperature measures the average kinetic (or motion) energy of the particles within a substance. Temperature measures an average because the particles within a substance do not all move at exactly the same speed. The particles in hotter substances are moving faster, whereas the particles in colder substances are moving slower.
Changing States of Matter
Thermal energy and temperature help us explain how matter changes from one state to another. Think about water as an example. The molecules in ice (solid water) are packed tightly together and just vibrating in place. The temperature of ice is low, 0°C or lower. The molecules in liquid water vibrate more and are constantly bumping into and sliding past each other. The temperature of liquid water is higher than ice, between 0°C and 100°C. The molecules in water vapor, a gas, move so fast that they spread far about. The temperature of water vapor, which is also called steam, is higher than liquid water, 100°C or higher. Matter can change state when thermal energy is transferred into or out of the substance. Ice melts and liquid water boils as thermal energy is added. Water vapor condenses and liquid water freezes as thermal energy is removed. Thermal energy always moves from a hotter area to a colder area, and this movement of thermal energy is called heat.