Explain why freezing, melting and burning are physical change
Answers
Answer:
When liquid water (H2O) freezes into a solid state (ice), it appears changed; However, this change is only physical as the the composition of the constituent molecules is the same: 11.19% hydrogen and 88.81% oxygen by mass. ... The melted ice cube may be refrozen, so melting is a reversible physical change.
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When you melt an ice cube (H2O), you have a physical change because you add energy. You added enough energy to create a phase change from solid to liquid. Physical actions, such as changing temperature or pressure, can cause physical changes. No chemical changes took place when you melted the ice. The water molecules are still water molecules.
Changing the Molecules
Iron atoms make new compounds as iron rusts. THe atoms combine with oxygen atoms.
Chemical changes happen on a much smaller scale. While some experiments show obvious chemical changes, such as a color change, most chemical changes are not visible. The chemical change as hydrogen peroxide (H2O2) becomes water cannot be seen since both liquids are clear. However, behind the scenes, billions of chemical bonds are being created and destroyed. In this example, you may see bubbles of oxygen (O2) gas. Those bubbles are evidence of the chemical changes.
Melting a sugar cube is a physical change because the substance is still sugar. Burning a sugar cube is a chemical change. Fire activates a chemical reaction between sugar and oxygen. The oxygen in the air reacts with the sugar and the chemical bonds are broken.
Iron (Fe) rusts when it is exposed to oxygen gas in the air. You can watch the process happen over a long period of time. The molecules change their structure as the iron is oxidized, eventually becoming iron oxide (Fe2O3). Rusty pipes in abandoned buildings are real world examples of the oxidation process.
Isomers
Isomers are compounds with the same number of atoms but have different structures. Glucose, galactose and fructose all have the formula C6H12O6. Some chemical changes are extremely small and happen over a series of steps. The resulting compounds might have the same number of atoms, but they will have a different structure or combination of atoms.
The sugars glucose, galactose, and fructose all have six carbon atoms, twelve hydrogen atoms, and six oxygen atoms (C6H12O6). Even though they are made of the same atoms, they have very different shapes and are called isomers. Isomers have atoms bonded in different orders.
Each of the sugars goes through different chemical reactions because of the differences in their molecular structure. Scientists say that the arrangement of atoms allows for a high degree of specificity, especially in the molecules of living things. Specificity means the molecules will only work in specific reactions, not all of them. For example, your body uses glucose as an energy source. If you eat galactose molecules, they need to be converted into glucose before your body can use them.
Answer:
Explanation
They can be changed.but burning is not a physical change because it only produces ashes