Physical And Chemical Change

A physical change affects only the physical properties of a substance, such as shape, size, colour, or state (solid, liquid, gas). No new substance is formed, and the change is usually reversible. Examples include melting of ice, tearing of paper, or dissolving sugar in water.

Ripening of a fruit is a chemical change because new substances are formed inside the fruit, such as sugars and different pigments. The change is irreversible. Melting of wax, breaking of glass, and freezing of water are physical changes.

Iron is more reactive than copper. Iron displaces copper from copper sulphate solution to form iron sulphate, which is green in colour. The blue colour of copper sulphate fades and turns green. A brown coating of copper metal also forms on the iron nail.

In a displacement reaction, a more reactive element displaces a less reactive element from its compound. Here, iron (more reactive) displaces copper (less reactive) from copper sulphate, forming iron sulphate and copper metal.

In a chemical change, mass is conserved but energy is always either absorbed or released. For example, burning wood releases heat and light. The statement no change in mass or energy is incorrect because energy change always happens.

When a candle burns, the wax melts (physical change) and the melted wax vaporises and burns to produce carbon dioxide, water vapour, heat, and light (chemical change). So both types of changes occur together.

Copper sulphate is an ionic compound made of copper (Cu²⁺) and sulphate (SO₄²⁻) ions. Its chemical formula is CuSO₄. It is usually seen as blue crystals because it contains water of crystallisation (CuSO₄·5H₂O).

Vinegar and baking soda undergo a chemical reaction that produces carbon dioxide gas. This gas forms bubbles and causes fizzing. This is an example of an acid-base reaction.

Rusting occurs when iron reacts with oxygen and moisture from the air to form a new reddish-brown substance called iron oxide (rust). This is a chemical change because a new substance is formed and the change is irreversible.

Melting of ice is a physical change because solid ice changes into liquid water. This change can be reversed by freezing the water back into ice. No new substance is formed.

Iron sulphate (FeSO₄) solution has a light green colour. In the reaction between iron and copper sulphate, the blue copper sulphate solution turns green because iron sulphate is formed.

In a chemical reaction, the original substances (reactants) change into new substances (products) that have different chemical properties. The atoms are rearranged, not destroyed or created.

Magnesium reacts with oxygen in the air when heated. It burns with a brilliant white flame and forms a white powdery substance called magnesium oxide (MgO). This is a chemical change.

Iron (Fe) displaces copper (Cu) from copper sulphate (CuSO₄) to form iron sulphate (FeSO₄). Iron has a +2 charge in this compound, so the formula is FeSO₄.

Digestion of food is a chemical change because complex food molecules are broken down into simpler ones by enzymes in our body. New substances are formed, and the change cannot be reversed.

When iron reacts with copper sulphate solution, iron displaces copper. The displaced copper metal gets deposited on the surface of the iron nail as a reddish-brown coating.

Boiling water into steam is a physical change. Steam can be cooled to get back liquid water. This change is reversible. The other options are chemical changes and cannot be reversed easily.

Iron causes copper to be reduced (gain electrons) from copper sulphate. In doing so, iron itself gets oxidised to iron sulphate. Therefore, iron acts as a reducing agent in this displacement reaction.

Baking a cake involves chemical changes. The heat causes the batter to rise, change colour, and form new substances with different taste and texture. This cannot be reversed.

In this displacement reaction, one iron atom displaces one copper atom from copper sulphate. The balanced equation shows iron and copper sulphate producing iron sulphate and copper metal.

Evaporation is a physical change because liquid water changes into water vapour. No new substance is formed. The water vapour can condense back into liquid water.

Iron sulphate (FeSO₄) is green in colour. As iron displaces copper from blue copper sulphate, the solution gradually turns green because iron sulphate is formed.

Breaking a glass tumbler is a physical change because the glass pieces are still glass. No new substance is formed. The change is irreversible but remains physical.

According to the law of conservation of mass, matter is neither created nor destroyed in a chemical reaction. Therefore, the total mass of reactants always equals the total mass of products.

Iron is higher than copper in the reactivity series of metals. This means iron can displace copper from its salt solution, as seen in the reaction between iron and copper sulphate.

Burning of a matchstick is a chemical change (combustion) that releases energy in the form of heat and light. Physical changes like melting and freezing do not release light.

Hydrated copper sulphate (CuSO₄·5H₂O) has five water molecules attached to each formula unit. These water molecules give the crystals and solution a deep blue colour. When heated, the water is lost and the compound becomes white.

In a physical change, the substance changes only in physical appearance or state. The chemical composition remains the same, so no new substance is formed.

Zinc is more reactive than copper. It displaces copper from copper sulphate, forming zinc sulphate (colourless) and copper metal (brown coating). The blue colour fades, and the solution may appear greenish due to impurities.

Photosynthesis is a chemical change because new substances (glucose and oxygen) are formed from carbon dioxide and water in the presence of sunlight and chlorophyll.

Sublimation is a physical change. Examples include dry ice (solid carbon dioxide) turning into gas, and camphor or naphthalene balls disappearing over time without melting.

Burning of wood is a chemical change because wood reacts with oxygen to form new substances like ash, carbon dioxide, water vapour, and smoke. The change is irreversible.

The iron nail gets a reddish-brown coating because copper metal is deposited on it. This happens as iron displaces copper from the copper sulphate solution.

Frying an egg is a chemical change because the egg white and yolk change their structure and colour due to heat. New substances are formed, and the change cannot be reversed.

In a decomposition reaction, one compound breaks down into two or more simpler substances. For example, when electricity is passed through water, it decomposes into hydrogen and oxygen gases.

Rusting is a slow chemical change that takes days, months, or even years depending on conditions. It requires the presence of oxygen and moisture.

When copper reacts with oxygen, carbon dioxide, and water from the air over a long time, it forms a green layer of basic copper carbonate (Cu₂(OH)₂CO₃). This is called patina and is a chemical change.

As iron reacts and dissolves into the solution as iron ions, the iron nail loses mass. At the same time, copper metal deposits on the nail, so the coating gains mass.

Breaking of glass is a physical change because the pieces are still glass. However, it is not easily reversible because we cannot join the broken pieces back into the original glass without special techniques.

Anhydrous copper sulphate (CuSO₄) does not contain water molecules. It is a white powder. When water is added, it becomes hydrated copper sulphate and turns blue.

Chemical reactions can release or absorb energy in different forms. Burning releases heat and light; explosions release sound; batteries produce electricity; some reactions absorb heat (endothermic).

When a plant needs energy, it breaks down stored starch into glucose. This is a chemical change because a new substance (glucose) is formed from starch.

When copper nitrate is heated strongly, it decomposes to form copper oxide, oxygen, and a reddish-brown gas called nitrogen dioxide (NO₂). This is a chemical change.

Baking soda (sodium bicarbonate) reacts with vinegar (acetic acid) to produce carbon dioxide gas, which causes bubbling and fizzing. This is a chemical change.

In a reversible physical change, no new substance is formed, and the change can be reversed by simple physical methods like heating, cooling, or dissolving. Example: melting of wax.

The displacement reaction between iron and copper sulphate releases a small amount of heat. This means the reaction is exothermic, so the temperature of the solution rises slightly.

Cooking involves chemical changes. Raw food materials change into cooked food with different taste, texture, and smell. New substances are formed, making the food easier to digest.

Silver reacts with hydrogen sulphide gas present in the air to form a black layer of silver sulphide (Ag₂S). This is a chemical change called tarnishing.

Condensation is a physical change where water vapour (gas) changes into liquid water. No new substance is formed, and the change can be reversed by evaporation.

Initially, copper sulphate solution is blue. As iron reacts and displaces copper, iron sulphate (green) is formed. The solution gradually changes from blue to green. At the same time, a brown coating of copper appears on the iron nail.