The Snow Maiden – Page 40

Freezing or freezing is the release of heat from a substance to change the substance from a liquid to a solid. In order for the change to occur, the temperature must be below the freezing point of the substance. Freezing of water is a reversible change, when heated, frozen ice turns into water when heated. Freezing water is a physical change. It is not a chemical change. A chemical change occurs when the atoms in a molecule are either added to or lost. Physical changes occur when the molecule alters its form. Water that is frozen retains the same chemical formula, so it is not a chemical change. The transformation of water into ice is a physical change because the hydrogen and oxygen molecules that make up water remain the same despite the transition from liquid to solid. When water freezes, only a change in state (from liquid to solid) occurs with the formation of ice, but no new substance is formed. If liquid water turns into ice, then it undergoes physical rather than chemical changes. In the case of water freezing, the water particles did not change their composition. What Happens When Water Freezes When water freezes into ice, some of its properties change, but the essence of water remains the same. Before and after the change, the same number of water molecules are present, and the chemical properties of water remain constant. However, to form water, hydrogen and oxygen atoms must undergo chemical transformations. The addition or subtraction of atomic bonds changes the chemical properties of the substances involved. Oxygen atoms are positively charged, while hydrogen atoms are negatively charged, so water molecules stick to each other like tiny magnets. The hydrogen "ears" form loose bonds with the oxygen "faces" of other water molecules, called hydrogen bonds. In ice crystals, their hydrogen bonds hold them together, like acrobats standing together, arms and legs stretched out. This provides more space between molecules in the crystal structure of ice than in liquid water. Liquid water molecules are like droplets, but in their solid (frozen) state they need their own space. Each water molecule is made up of two hydrogen atoms (white) and one oxygen atom (red). This equation says that it takes two hydrogen molecules and one oxygen molecule to form two water molecules. This equation says that six carbon dioxide molecules combine with six water molecules to form one sugar molecule and six oxygen molecules. Light Provides Energy However, light energy does not produce the atoms that make up these sugars—which would violate the law of conservation of mass—it simply provides energy for chemical change. When water turns into a solid or gas, we say that it goes into another state of matter. Although the physical form of water changes, its molecules remain the same. When an ice cube melts, its shape changes as it gains the ability to flow. Matter can change form through physical and chemical changes, but with each of these changes, matter is preserved. Water is a very clear example of how matter moves in circles in our world, often changing shape but never disappearing. When water evaporates, it changes from liquid to gaseous, but it is still water; it has not changed in any other substance. The Physics of Boiling Water Boiling water is an example of physical and non-chemical change because water vapor still has the same molecular structure as liquid water (H2O). Since the actual molecular structure of water does not change and there is no chemical reaction involving water molecules, the transition is a physical change. A phase transition is a physical change because the molecules stay the same, but the chemical composition of the material does not change. The freezing of water to ice and the evaporation of water are physical changes because both processes are reversible and can be returned to their physical states. Melting, boiling, or freezing simply by changing temperature are examples of physical changes, as they do not affect the internal composition of an object or objects. Types of physical changes include boiling, tarnishing, dissolving, freezing, freezing, freezing, liquefying, melting, smoking, and evaporating. When the physical temperature changes, a substance, such as water, heats up. Water, like all other types of matter, requires the addition or removal of energy in order to change state. What Happens When Ice Melts When heat (a form of energy) is added, the ice melts and turns into liquid water. The removal of heat causes water (liquid) to freeze, forming ice (solid). When water becomes solid, it releases heat, warming the environment. Freezing occurs at temperatures below 0 degrees Celsius with water, while some other liquids become solid at higher or lower temperatures. Therefore, freezing a substance will not change its chemical composition, but its state. TL; DR (Too Long; Not Read) Physical changes affect the physical properties of a substance, but do not change its chemical structure. Examples of physical properties include melting, volatilization, change in strength, change in durability, change in crystal shape, structural change, shape, size, color, volume, and density. These changes are an integral part of our daily lives, such as food digestion, combustion, osmosis, and phase transitions. Research shows that students often use the term "chemical change" to describe changes in physical condition. If students view ice as a substance other than liquid water, they are likely to classify the melting of ice as a chemical change. Students can view the dissolution of potassium permanganate (Condys crystals) in water as a chemical change due to the strong color difference. The Conditions of Saltwater For example, the dissolution of salt in water is usually considered a physical change, however the chemicals in saline (sodium hydrate and chloride ions) are different from those in solid salt. The dissolution of water-soluble coffee appears to be a physical change, but in most cases the dissolution is accompanied by an energetic change and is probably best viewed as a chemical process, although the original components can be recovered by physical means. However, understanding the difference between purely physical processes such as melting, evaporation, and boiling, and the changes that occur in chemical reactions, especially the idea that new substances are formed, is important for understanding chemistry and for students who often confuse the two. The difference in this case is that the substances before and after the change have different physicochemical properties. Some non-metals, such as oxygen and radon, change color with phase transitions. This is an interesting example because a state change can cause a color change, even though the chemical composition before and after the change is the same. In their experiments, the children put the same amount of material -- the same amount of water -- in both cups but when they froze the water, the volume changed. After the water in the cups freezes, return the two cups to each set. To share with the kids, you will now freeze one of each set in a glass of water overnight, or until the next time you see them.