Freezing

Freezing is the process when a liquid changes into a solid because its temperature gets colder than a certain point called the freezing point. When a liquid freezes, its molecules slow down because they lose heat energy. Then, the molecules line up in a neat and fixed pattern to form a solid. This change from liquid to solid is very important in many parts of nature and technology. For example, freezing affects the weather, helps keep food fresh, and is important in making materials and in living things. Freezing is the opposite of melting, and when it happens, heat is released from the liquid as it turns solid. The freezing point is the exact temperature where a liquid and its solid form can exist together without changing. This usually happens at normal air pressure, like the pressure around us. For pure liquids, like pure water, the freezing point is always the same temperature. But for mixtures, like salty water, the freezing point can change depending on what is mixed in. This is why salty seawater freezes at a lower temperature than pure water. Other things, like dirt or tiny particles (called nucleating agents), and changes in pressure can also affect how and when a liquid freezes by helping or slowing down the way crystals form.^[1][2]

Water dripping from a slab of ice and then freezing, forming icicles

Freezing happens in two main steps: nucleation and growth. Nucleation is the very first step, where tiny groups of molecules come together to form a small solid "seed." This seed is stable enough to start growing bigger. Nucleation can happen in two ways. Sometimes it happens inside the liquid by itself (called homogeneous nucleation). Other times, it happens on surfaces or on tiny impurities, like dust particles, which help crystals form (called heterogeneous nucleation). How fast freezing happens and what kind of crystals form depends on things like how quickly the liquid cools down, how pure the liquid is, and whether there are other substances mixed in. Scientists use this knowledge to control freezing in things like food storage and making medicines.^[3]

Freezing is very important for nature and the Earth's climate. When water freezes in oceans, lakes, and rivers, it affects the animals and plants living there. It also helps control how heat moves around the planet. Freezing happens every season and changes the soil, which affects how plants grow. Scientists also use freezing to help save biological samples and organs, a process called cryopreservation.^[4] Freezing water is also part of many weather events, like frost on the ground, hail falling from the sky, and snow forming in the clouds.^[5] Freezing is very useful in technology and everyday life. For example, freezing food helps keep it fresh for a longer time. When food is frozen, bacteria and enzymes that cause spoilage slow down or stop working, so the food stays good.^[6] Freezing is also used in different industries. It helps in freeze drying food, making metal and plastic parts, and producing very cold fuels called cryogenic fuels. Knowing how freezing works and controlling it is important in many areas, from farming to building airplanes and rockets.^[7][8]

Freezing is a process where a liquid turns into a solid, and during this change, heat is released. This heat is called the latent heat of fusion. Even though the liquid is cooling, its temperature stays the same while it is turning into ice until all of it has frozen.^[9] Scientists have studied freezing a lot and have created special chemicals called antifreeze agents. These antifreeze agents can change the freezing point of liquids, which means they stop ice from forming easily. Antifreeze is used in cars to keep the engine from freezing in cold weather. It is also used to protect living things like plants and animals by stopping ice from damaging their cells.^[10][11]

Related pages

• Freezing point
• Condensation
• Melting
• Vaporization
• Sublimation