Chemical and Physical Change

Every day you experience a variety of changes around yourself starting from days turning into nights to cooking food, buring of fuel, etc. They can be period, non-periodic, natural or man-made. However, on a larger front, changes are classified into two categories physical and chemical change.

So, what are physical and chemical changes? You need to know their differences in detail, not just for your examination, but also to understand other vital topics in this standard and the future. These are discussed below in detail.

Physical Change

The changes which are restricted to changes in the display, but no change occurs in the composition is called a physical change. They are also known as temporary changes because the change takes place for a particular period.

Some examples of temporary change are lighting of a bulb, heating a rod, changing of ice into water, etc.

Physical properties consist of several other features of a product, and they are:

• Lustre (shine)

• Malleability (can be beaten into sheets)

• Density

• Viscosity

• Solubility

• Mass

• Volume

• Ductility (can be drawn into thin wires)

Any alteration in the above mentioned physical properties is counted as a physical change.

Physical Changes which are Common

• Texture

A substance’s texture can vary with a physical change. For instance, if a wooden piece undergoes sanding, waxing and polishing, it will have a completely different texture than its initial state which was of a rough wood piece.

• Colour

Colour change does not indicate a chemical change. For example, changing the colour of a metal does not alter its physical properties. However, for a chemical reaction, change in colour is generally a sign that a reaction is taking place. By painting a metal object, it does not have any effect on the composition of the same. In fact, you can again paint it with some other colour. This is an example of a temporary change.

• Temperature

You cannot notice a change in temperature until there is any change of state. This is another physical change. Suppose if you have put an empty pan on a burning gas oven. You will not see any change in the shape, texture, colour, etc. of a pan. However, if you touch it, then only can you feel the heat, and it may even cause a burn. Similarly, if the pan is kept idle on a cupboard, it will become cold. No one can see this change visually; you have to use a thermometer or other apparatus to measure it.

• Shape

Change in the shape of an object can take place, and yet it may remain fixed to its original composition. Consider if you have folded a hundred rupee note, the note is still the same chemically.

• Change of state

State change is another physical change. Here, many physical properties are seen to get changed, like shape and viscosity. When ice melts and becomes water, it does not go back to its solid shape automatically but becomes a viscous liquid.

Physical Properties of a Substance

• Lustre

An element’s lustre is defined by the way it behaves when light falls on it. Lustre is a prime quality of metals. More or less all metals, metalloids and transition metals are lustrous. Gas and non-metals do not have the property of lustre.

• Malleability

Another quality of metals is malleability. The word malleability means that metal elements can be deformed by exerting a certain amount of stress. For instance, if a piece of metal is hit with a mallet and deformation takes place, it is considered malleable. A small metal paperclip can be shaped just with bare hands.

• Ductility

As mentioned earlier, ductility is the property of metals that allows it to be drawn into thin wires. Raw copper can be attained and then purified and wrapped into a coil. Non-metals do not hold this property.

• Density

An object’s density is its mass by volume. A body having a higher mass will have a high density in a constant amount of volume. For instance, a metal ball whose size is similar to that of a baseball is compressed from raw metal. Now, compare this with a paper made baseball. The metal baseball is much heavier in its same volume amount. Hence, metal baseball has high density. Moreover, the density of an object is the factor which determines whether it will float or sink in any chemical fluid. The density of water is 1 g/cm3, so any object that has density lesser than 1 g/cm3 will float and the objects having density more than 1 g/cm3 will sink in water.

• Viscosity

Viscosity refers to the deformation resistance of a specific chemical substance when force is exerted on it. Another way to think about viscosity is in regards to thickness. Thick substances have high viscosity than substances which are deemed ‘thin’. Honey and magma have much higher viscosities as compared to water.

Chemical Change

Chemical changes are quite different. A chemical change refers to a change in the composition of a substance. When bonds get broken, and new substances are formed. Following are the signs of chemical changes:

• Temperature change

• Colour change

• Noticeable odour or smell (after the beginning of reaction)

• Precipitate formation

• Bubble formation

Note: When two or more than two reactants are blended, and change in colour, temperature, etc. is seen, it is said that a chemical reaction is taking place. However, these are not precise indicators. It may happen that a chemical reaction is not occurring. Colour change of a substance is not always considered a chemical change. For example, if you are painting your car, it is not a chemical change; rather it is a physical change. The reason behind this is that the car’s composition has not altered.

Chemical Changes that are Common

• Temperature Change

Change in temperature is a trait of a chemical change. In experiments, one may insert a thermometer into the experimenting vessel to measure the temperature. If it rises (it does in maximum cases), a chemical change is taking place. Physical temperature change is different from this one. At the time of a physical change, for example, one substance like water is boiled. However, in case of a chemical change, one substance is mixed with another, and they yield a product.

• Colour Change

Change in colour of a substance is another feature of a chemical reacting. Suppose if you keep an eye on the rusting of iron, you will notice than colour change has occurred in the metal object and it has turned orange. However, again, you must remember that painting any object is not a chemical change.

• Odour

When more than one elements or compounds are mixed, an odour or scent is emitted by the reaction; it is a chemical change. For example, you must have seen rotten eggs which have foul odour is an example of a chemical reaction and occurs due to chemical decomposition. This is an example of a permanent change.

• Precipitate Formation

This property is the most common indicator of a chemical reaction. The solid that forms within another solid or a solution is called a precipitate. However, it should not be jumbled with suspensions. For example, when soluble carbonate undergoes reaction with barium, a precipitate of barium carbonate is formed.

• Bubble Formation

This is one more sign of a chemical reaction. When there is a formation of bubbles, change in temperature can also take place. These two things can occur simultaneously. For example, if sodium carbonate reacts with hydrochloric acid, it can yield bubbles, but enough hydrochloric acid must be present for the bubbles to be seen.

Below you will find a physical and chemical change worksheet that you must solve on your own to understand physical and chemical changes more clearly.

Question. Determine which of the following changes are physical or chemical:

1) cutting of hair, 2) mixing water with sugar, 3) making a mixture of pretzel, peanut and cereal, 4) reaction of baking soda with vinegar and yielding of a gas, 5) a metal piece is bent to half, 6) on burning methanol, it leaves a residue, 7) an aspirin tablet is crushed into dust, 8) on exposure to the environment, copper turns green, 9) resultant liquid becomes yellow when two clear liquids are mixed, 10) baking of cookies, 11) glass is scratched by diamonds, 12) burning of tree produces ash, 13) crumpling up a piece of paper, 14) freezing of water to ice.

The Chemical and Physical Change Worksheet Answer Key is Given In The Below Table:

Chemical and physical changes are an important concept of Chemistry which deals with various properties of matter. You must study them thoroughly to know the difference between physical and chemical changes.

Furthermore, you can download our Vedantu app to get access to online classes and study materials with ease.