HOTS Questions: Matter in our Surroundings for Class 9 - Free MCQ Test

Higher the melting point of a substance, greater will be the force of attraction between particles. The melting point of iron is considerably high, so the force of attraction between its particles is higher.

A gas is a substance with no definite volume and no definite shape. Solids and liquids have volumes that do not change easily. A gas, on the other hand, has a volume that changes to match the volume of its container. The molecules in a gas are very far apart compared with the molecules in a solid or a liquid.

The change of state from solid to liquid is known as Melting. This is a process in which a solid substance changes into a liquid on heating. Heat energy is required to break the bonds between molecules, allowing them to move around freely. This process is also known as fusion, and the amount of energy required is called the latent heat of fusion. In a phase diagram such as Figure 12.4.1, the melting point is the temperature at which a substance can transition from a solid to a liquid.

Dry ice, sometimes referred to as "cardice", is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue. 

Formula to change the value of celsius into kelvin is K = C + 273. As we know that boiling point of water is 100 c. SO, K = 100 + 273 K = 373 k.

The process of conversion of a substance from the liquid state to its vapor state at any temperature below boiling point is called evaporation or vaporization.

The turning of any liquid into vapour is called Evaporation. The factors affecting the evaporation are:

1. Temperature. As the temperature increases, the rate of evaporation also increases.

2. Surface Area. As the Surface area increases, the rate of evaporation increases.

The higher the temperature of liquid, the faster the rate of evaporation. This is due to the fact that as the liquid's temperature increase, the molecule of the liquid move about faster, thus increasing the rate of evaporation.

A fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas, and to some extent, plastic solids.

Sublimation is when a substance changes directly from a solid to a gas, skipping the liquid stage.

An example is naphthalene, commonly used in mothballs.

Key points about sublimation:

• Naphthalene balls disappear over time without leaving a solid behind.
• This happens because the solid naphthalene converts directly into a gas.
• Other substances like sugar and nitrogen do not sublimate under normal conditions.

Thus, sublimation is a special phase change observable in substances like naphthalene.

The process of changing from gaseous state to liquid state on cooling is called condensation. On cooling the kinetic energy of particles decreases and intermolecular forces of attraction increases therefore gas converted into liquid.

When a liquid is heated, it eventually reaches a temperature at which the vapor pressure is large enough that bubbles form inside the body of the liquid. This temperature is called the boiling point

The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. For ice, the melting point is 0°C at which ice a solid turn to water.

In gases, the atoms are much more spread out than in solids or liquids, and the atoms collide randomly with one another. A gas will fill any container, but if the container is not sealed, the gas will escape. Gas can be compressed much more easily than a liquid or solid.

A drop of ink spreads in a beaker of water through diffusion. This is because the particles in liquids can move around each other, which means that eventually they are evenly mixed. Diffusion is the process of a substance spreading out to evenly fill its container or environment. In a solution, a concentrated solute diffuses to spread evenly in its solvent. concentration to low concentration. 

Correct Answer- Option A

• The melting point is the temperature at which a solid becomes a liquid under atmospheric pressure.
• At this point, the solid and liquid phases coexist in equilibrium.
• The process involves enough energy being absorbed by the solid to overcome the forces holding its particles in a fixed position.
• This concept is distinct from the boiling point, which is the temperature at which a liquid turns into a gas.
• Diffusion and evaporation are unrelated to phase changes from solid to liquid.

To convert 373°C to the Kelvin scale:

Use the following formula:

• K = °C + 273

Now, applying the formula:

• K = 373 + 273
• K = 646

Therefore, the temperature of 373°C is equal to 646 K.

We know that °C = K - 273.15

C= K - 273
C= 270 - 273
C = -3

A plasma is a hot ionized gas consisting of approximately equal numbers of positively charged ions and negatively charged electrons. The characteristics of plasmas are significantly different from those of ordinary neutral gases so that plasmas are considered a distinct "fourth state of matter."

Sublimation is the process through which the solid substance changes directly into vapors or a gaseous state without passing through a liquid state. Dry ice is a common example of this process.

At low pressure

Explanation: Boiling occurs when the vapor pressure of a liquid equals the external pressure. At lower pressures, the boiling point of water decreases. So, if the external pressure is reduced significantly (below atmospheric pressure), water can boil at room temperature. This phenomenon can be observed in a vacuum chamber, where the pressure is significantly reduced, allowing water to boil at room temperature.

Diffusion is the property of matter which is based on the motion of its particles. Diffusion occurs in gases, liquids and solids. Diffusion is fastest in gases and slowest in solids. The rate of diffusion increases on increasing the temperature of the diffusing substance.

Evaporation causes cooling because the process requires heat energy. The energy is taken away by the molecules when they convert from liquid into gas, and this causes cooling on the original surface.

It's true because camphor is sublime and it changes directly into gas without passing through the state of liquid. The process in which solid directly changes into gas without passing through the state of liquid is called sublimation.

Boiling Point: The temperature at which the liquid boils and changes into gaseous state at the atmospheric pressure is called boiling point. For example, water boils at 100°C to form water vapour (at 76 cm pressure).

Surface phenomenon is a process in which only the surface of any substance or object is involved in the process. In Evaporation only the surface of the liquid involves in the process, its bulk remains unaffected by evaporation. Hence, it is a surface phenomenon.

Intermolecular force refers to the force that exists between two or more molecules. 

Intermolecular force of attraction is maximum in solids. 

This is because molecules in solid remain very close to each other which allot a definite shape to the objects that are solid. 

It is lesser in liquids and least in the gases.

Evapouration is the process by which water turns to water vapour and condensation from vapours to water. So evapouration is opposite of condensation freezing is the process by which water turns to ice and melting is ice to water.so freezing is opposite of melting as both of them are true, Option A is correct!

The large volumes of gases can be put into small volumes of cylinders because of their property known as compressibility. This is possible because of the large inter particle distance and weak force of attraction between the particles of gas.

The kinetic energy of molecules
K = 3/2 kB. T
K = average kinetic energy per molecule of gas (J)
kB = Boltzmann's constant ()
T = temperature (k)

Additional Explanation

1. The kinetic energy of the molecules of a substance can be defined as the average energy associated with the molecule due to its vibrational motion.
2. Kinetic energy of the molecules is directly proportional to the temperature.
3. Increasing temperature increases the speed of vibration and hence the kinetic energy too and vice-versa.