What Happens to the Speed of Molecules as They Absorb Heat?

Heat and Matter

• The known universe is comprised of matter and energy, both of which are very closely linked. What you see as solid matter is actually made of tiny building blocks called molecules. Molecules are propelled by energy and are never stationary. As molecules move around, they also collide into one another endlessly, and this kinetic energy transforms into thermal energy, or heat. The sensation you feel when you get warmer is the result of many molecules colliding with the molecules in your skin.

Heat and Energy

• Energy cannot be created or destroyed; it only changes form. Heat, or thermal energy, is one of those forms and is present in many conversions. For example, when lightning, or electrical energy, strikes a surface, it converts to thermal energy, causing the surface to heat up. If you quickly rub your hands together, such as when you are cold, that kinetic energy of your hands causes your skin to warm. Thermal energy is created from other energy in the same manner.

Adding Energy to Molecules

• Matter is made of molecules, and molecules are always moving and colliding with one another. However, different molecules move at different speeds, and when they collide, there is a transference of energy. That energy causes the molecules to move even faster, colliding more often and causing an increase in temperature. As matter absorbs more thermal energy, its molecules gain additional energy, which in turn cause them to move at higher speeds. Higher speeds cause more powerful collisions, causing molecules to rebound with more force as well. This is why matter expands slightly as it is heated up.

Testing the Phenomena

• You can test the increased speed of molecules that results from having more thermal energy using two clear bowls of water and food coloring. To conduct the experiment, fill both bowls with equal amounts of water. Use cold water in one bowl and hot water in the other. Allow both bowls of water to be still as you pour in equal amounts of food coloring into each bowl. You will notice that the food coloring behaves differently in each bowl. The bowl with more collisions between food coloring and water molecules will spread the food coloring faster.