Olympiad Test: Matter - 2 - Class 5 MCQ

The diagram has two boxes, one in which molecules are tightly packed and the other one in which the molecules are slightly loosely packed. Here solid is slowly converting to liquid state which occurs during melting. While, boiling is the process where a liquid turns into a gas. In this state change, particles gain enough energy to move freely and spread out, which does not match the situation described in the question.

In physical changes, the state of matter changes, but the substance itself remains the same and can be returned to its original form. This type of change is called reversible because it can be undone without altering the substance's basic nature. For example, water freezing and melting is a reversible physical change.

In the given scenario, the process shown is evaporation. This occurs when:

• Heat from the sun warms the water.
• Water changes from a liquid to water vapor.

Key characteristics of evaporation include:

• It happens at the surface of the liquid.
• It does not require the liquid to reach its boiling point.
• It differs from boiling, which occurs throughout the liquid at a specific temperature.

The melting point is defined as the temperature at which a solid transforms into a liquid. At this point:

• The solid absorbs sufficient heat energy.
• This energy enables the particles to overcome their binding forces.
• Consequently, the solid melts and becomes a liquid.

Matter is composed of tiny particles known as atoms. These atoms serve as the fundamental building blocks of matter.

Key points about atoms:

• They combine in different ways to create molecules.
• Molecules are the structures that form all types of substances.
• Atoms are essential for understanding the composition of matter.

The burning of wood is a chemical change because it creates new substances, including:

• Ash
• Carbon dioxide
• Water vapor
• Other gases

This process involves a chemical reaction known as combustion, which is irreversible. The original properties of the wood are completely altered.

• Statement A: Physical change is generally reversible, meaning that the substance can return to its original form (e.g., water freezing and melting).
• Statement B: Chemical change is typically irreversible, as it results in the formation of new substances that cannot easily be turned back to their original form (e.g., burning wood to form ash).

Therefore, only Statement B is true.

Water is a liquid, and liquids do not have a fixed shape. They take the shape of their container, which is why we can't make a statue out of water. A statue requires a material with a definite shape, which liquids like water do not have. Therefore, Option A is correct.

A chemical change happens when one form of matter transforms into another kind of matter. This involves a process where:

• The original substance undergoes a transformation.
• New substances with distinct properties are formed.
• Examples include burning wood, which turns into ash, carbon dioxide, and water.

Such changes are permanent, meaning the original matter cannot be easily restored.

Freezing is the process where a liquid transforms into a solid. The opposite of freezing is melting, which occurs when a solid changes back into a liquid. This process involves:

• Transition from a solid state to a liquid state.
• Increased temperature, as the solid absorbs heat.

In summary, melting is the direct reversal of freezing.

Boiling is a process that occurs at a specific temperature called the boiling point. During boiling, the entire liquid transforms into gas. In contrast:

• Evaporation can happen at a range of temperatures, even below the boiling point.
• It occurs only at the surface of the liquid.

In summary, boiling is distinct because it requires a specific temperature and affects the whole liquid, whereas evaporation is more gradual and can happen at various temperatures.

When the jeweller melts pure gold, he is converting solid gold into liquid gold. This process involves a physical change where the state of the gold changes but it remains gold throughout.

Key points to consider:

• The weight of pure gold remains the same in both solid and liquid forms.
• Therefore, after melting, the jeweller has 100 gm of gold.
• As a result, he will receive the price for 100 gm of gold.

Gases consist of particles that are very far apart and thus move easily.

As seen in the diagram, there are small water drops on the window. These water drops can be seen as a result of the conversion of water vapour in the air back into the water form. Thus this depicts the process of condensation.

Desublimation is the process where a gas (water vapor) directly changes into a solid (ice) without passing through the liquid state. This process is also known as deposition. It is the reverse of sublimation, where a solid directly turns into a gas.

The conversion of ice into water is an example of melting. This process occurs when a solid (ice) absorbs heat and transforms into a liquid. Key points include:

• Melting happens at a specific temperature called the melting point.
• During melting, the energy absorbed breaks the bonds holding the solid structure together.
• This transition is a fundamental concept in thermodynamics.

A liquid has a definite volume but lacks a definite shape. Here are some key characteristics:

• It adopts the shape of its container.
• It maintains a fixed volume regardless of the container's shape.
• Unlike solids, liquids do not have a fixed shape.
• Unlike gases, liquids do not expand to fill the entire space available.

The melting of ice is a physical change. It involves a transition from solid to liquid without changing the chemical composition of the substance.

• When ice melts, it simply changes state.
• No new substances are formed during this process.
• This distinguishes it from chemical changes, where the identity of the substance changes.

The conversion of a solid directly into a gas, without passing through the liquid state, is known as sublimation. Here are some key points about this process:

• Sublimation occurs when molecules in a solid gain enough energy to enter the gas phase.
• Common examples include the transformation of dry ice (solid carbon dioxide) into carbon dioxide gas.
• This process can be observed with substances like mothballs (naphthalene) and snow in very cold conditions.

Baking a cake involves both chemical change and irreversible change. The process includes:

• Ingredients undergoing a chemical transformation, such as rising due to baking powder.
• The creation of new substances during baking.
• Once baked, the cake cannot revert to its original ingredients, confirming it as an irreversible change.