The conversion of water to ice is considered a physical change, whereas the conversion of iron to rust is considered a chemical change. Why?
A chemical change is a change in which something new is formed
Physical change is a change in which the substance changes form but keeps its same chemical composition
In ice, each of the molecules is connected to the molecules next to it, making it hard. Freezing is a change of state of a material and it is a physical (not a chemical) change
A rectangular container measuring 28 cm 43 cm 58 cm is filled with water. What is the mass of this volume of water in kilograms and grams? (Take the density of water to be 1000 kg/m3.)
kg
g
The conversion of water to ice is considered a physical change because it involves a change in the physical state of the substance without any change in its chemical composition. In other words, the water molecules rearrange themselves into a regular lattice structure when freezing without any alteration to their chemical properties. This change is reversible, meaning that ice can be melted back into water by providing heat.
On the other hand, the conversion of iron to rust is considered a chemical change because it involves a chemical reaction between iron and oxygen in the presence of water or moisture. This reaction, known as oxidation, results in the formation of a new compound called iron(III) oxide or rust. Unlike freezing water, the formation of rust involves a change in the chemical composition of the iron, as its atoms combine with oxygen to create a new substance with different properties. Once iron is converted to rust, it cannot be easily reversed back to its original form without undergoing a separate chemical process.
The conversion of water to ice is considered a physical change because it involves a change in the physical state of water without altering its chemical composition. When water freezes, its molecules slow down and come closer together, forming a crystalline structure. However, the H2O molecules remain intact, and no new substances are formed.
On the other hand, the conversion of iron to rust is considered a chemical change (specifically, an oxidation reaction) because it involves a chemical reaction that changes the composition of the substance. When iron reacts with oxygen and water in the presence of certain impurities, it forms hydrated iron(III) oxide, commonly known as rust. During this process, the iron atoms combine with oxygen and undergo a chemical transformation, resulting in the formation of a new compound with different properties.
To understand why these conversions fall into different categories, we can examine the key characteristics of physical and chemical changes:
1. Physical change: In a physical change, only the physical properties, such as size, shape, or phase, are altered, while the chemical composition remains unchanged. The change is generally reversible, meaning the substance can revert to its original state without forming any new substances.
2. Chemical change: In a chemical change, the chemical composition of a substance is altered, resulting in the formation of one or more new substances with different properties. Chemical changes typically involve breaking or forming chemical bonds, resulting in a change in the arrangement of atoms.
By understanding the nature of the processes involved in the conversion of water to ice and iron to rust, we can conclude that the former is a physical change and the latter is a chemical change.