Very Shory Answer – Class 9- Chemistry – CH 1 -Matter In Our Surroundings

Q1. What is sublimation?

Sublimation is the process in which a substance transitions directly from the solid phase to the gas phase without passing through the intermediate liquid phase. In this process, the substance absorbs heat energy, causing its particles to gain enough kinetic energy to break free from the solid lattice and enter the gas phase. Examples of substances that undergo sublimation include dry ice (solid carbon dioxide) and mothballs (naphthalene).

Q2. What are the characteristics of the particles of matter?

The characteristics of particles of matter include:

Particles have mass and volume.

They are in constant motion, with varying speeds depending on the temperature.

They attract each other due to intermolecular forces.

They are arranged in different states of matter: solid, liquid, and gas.

They have negligible volume compared to the volume of the entire substance they compose.

Q3. Will increase or decrease of pressure help to liquefy a gas?

Increasing pressure generally helps to liquefy a gas, while decreasing pressure tends to favor the gas phase. According to the phase diagram of a substance, increasing pressure at constant temperature can cause a gas to condense into a liquid if the pressure is above the substance’s critical pressure. Similarly, decreasing pressure can cause a liquid to vaporize into a gas.

Q4. Define: Boiling point, Melting point

Boiling point: The boiling point of a substance is the temperature at which its vapor pressure equals the atmospheric pressure, causing the liquid to boil and transition into the gas phase.

Melting point: The melting point of a substance is the temperature at which it changes from the solid phase to the liquid phase.

Q5. Define: (a) Latent heat of fusion (b) Latentheat of vaporisation.

Latent heat of fusion: The latent heat of fusion is the amount of heat energy required to change a unit mass of a substance from the solid phase to the liquid phase at its melting point, without a change in temperature.

Latent heat of vaporization: The latent heat of vaporization is the amount of heat energy required to change a unit mass of a substance from the liquid phase to the gas phase at its boiling point, without a change in temperature.

Q6. Give reasons:

(a)  A gas fills completely the vessel in which it is kept:

(b) A gas exerts pressure on the walls of the container

(a) A gas fills completely the vessel in which it is kept: This happens because gas particles have negligible volume compared to the volume of the container. They move freely and rapidly, spreading out evenly to fill the available space.

(b) A gas exerts pressure on the walls of the container: Gas particles are in constant motion and collide with the walls of the container. These collisions create pressure, known as gas pressure, exerted by the gas on the container walls.

Q7. What is plasma?

Plasma is the fourth state of matter, distinct from solid, liquid, and gas. It is an ionized gas consisting of positively charged ions and free electrons. Plasma occurs at high temperatures, such as those found in stars, lightning bolts, and certain industrial processes. Examples of plasma include the sun’s surface, fluorescent light bulbs, and plasma TVs.

Q8. What are the full forms of CNG and LPG? Write their uses.

CNG: Compressed Natural Gas

Uses: CNG is primarily used as a fuel for vehicles, particularly in buses, taxis, and personal vehicles. It is considered a cleaner alternative to gasoline or diesel, as it produces fewer emissions.

LPG: Liquefied Petroleum Gas

Uses: LPG is commonly used for cooking, heating, and as a fuel in vehicles. It is stored in liquid form under pressure but vaporizes when released from its container, making it convenient for use in various applications.

Q9.(a) Change the following Celsius temperatures to the Kelvin scale:

(i)-2730C  (ii)-1000C  (iii)-400C  (iv) + 300C

(b) Convert: (a) 300 K (b) 573 K into celsius scale

Ans:

(a).(i) -273°C = 0 K (absolute zero)

(ii) -100°C = 173 K (add 273 to Celsius temperature)

(iii) -40°C = 233 K

(iv) +300°C = 573 K

(b). Convert: (a) 300 K (b) 573 K into celsius scale

(a) 300 K to Celsius scale:

300K-273 =27°C

(b) 573K – 273 =300°C

Q10. Why does our palm feel cold when we put some acetone petrol as perfume on it?

When acetone or any other volatile liquid evaporates from our skin, it absorbs heat energy from the surroundings (including our skin) to overcome the intermolecular forces holding the liquid molecules together. This rapid absorption of heat causes a cooling sensation on the skin, making it feel cold.

Q11. How do aquatic plants and animals survive? From where do they get oxygen?

Aquatic plants produce oxygen through the process of photosynthesis, where they use sunlight to convert carbon dioxide and water into oxygen and glucose. Aquatic animals obtain oxygen dissolved in water through their gills or other respiratory structures, extracting it from the surrounding aquatic environment.