Freezing is a common physical process that transforms a liquid into a solid. This common phenomenon, like water turning into ice or frost forming, involves a fundamental change in a substance’s energy. A frequent question arises regarding whether this process releases or absorbs energy from its surroundings. Understanding the energy dynamics of freezing requires distinguishing between two primary types of energy changes.
Understanding Energy Changes
Processes in nature can either release or absorb energy from their surroundings. An exothermic process releases energy, typically in the form of heat, into the environment. This release of energy often results in a warming effect on the surroundings. Chemical hand warmers, for instance, demonstrate an exothermic process as they generate warmth you can feel.
Conversely, an endothermic process absorbs energy from its surroundings. This absorption of energy usually leads to a cooling effect on the immediate environment. An example of an endothermic process is an instant cold pack, which feels cold to the touch because it draws heat away from your skin.
Freezing: Releasing Energy
Freezing is an exothermic process, meaning it releases energy into its surroundings. As a liquid transforms into a solid, its molecules slow down and arrange themselves into a more ordered, rigid structure. This transition to a more stable, lower-energy state necessitates the release of excess kinetic energy from the molecules.
The energy released during freezing is known as the latent heat of fusion. For water, approximately 334 kilojoules of energy are released for every kilogram that freezes at 0°C. This heat must be continuously removed from the liquid for the freezing process to continue. The temperature of the substance itself remains constant during this phase change until all of it has solidified, as the released energy is associated with the change of state rather than a change in temperature.
Everyday Examples
Beyond freezing, other exothermic processes include the burning of wood or natural gas, where combustion reactions release significant heat and light. The setting of concrete also involves an exothermic reaction, slowly releasing heat as it hardens.
Melting ice, for example, absorbs heat from its surroundings, which is why ice helps cool down a beverage. The evaporation of sweat from your skin is another endothermic process; it draws heat from your body, providing a cooling sensation.