Chapter 1 Matter in Our Surroundings Solutions
Question - 1 : - Which of the following are matter?
Chair, air, love, smell, hate, almonds, thought, cold, lemon water, smell of perfume.
Answer - 1 : -
The following substances are matter:
Chair
Air
Almonds
Lemon water.
Question - 2 : - Give reasons for the following observation:
The smell of hot sizzling food reaches you several meters away, but to get the smell from cold
food you have to go close.
Answer - 2 : -
Particles in the air, if fueled with higher temperatures, acquire high kinetic energy which aids them
to move fast over a stretch. Hence the smell of hot sizzling food reaches a person even at a distance
of several meters.
Question - 3 : - What are the characteristics of the particles of matter?
Answer - 3 : -
The characteristics of particles of matter are:
(a) Presence of intermolecular spaces between particles
(b) Particles are in constant motion
(c) They attract each other
Question - 4 : - The mass per unit volume of a substance is called density. (density=mass/volume). Arrange the following in the order of increasing density – air, exhaust from the chimneys, honey, water, chalk, cotton and iron.
Answer - 4 : -
The following substances are arranged in the increasing density:
Air
Exhaust from chimney
Cotton
Water
Honey
Chalk
Iron
Question - 5 : - Answer the following.
a) Tabulate the differences in the characteristics of matter.
b) Comment upon the following: rigidity, compressibility, fluidity, filling a gas container, shape, kinetic energy and density.
Answer - 5 : -
(a) The difference in the characteristics of the three states of matter.
| Characteristics | Solid | Liquid | Gas |
| Shape | Fixed shape | No Fixed shape | No Fixed shape |
| Volume | Fixed volume | Fixed volume | No Fixed volume |
| Intermolecular force | Maximum | Less than solids | Very less |
| Intermolecular space | Very less | More than solids | maximum |
| Rigidity/Fluidity | Rigid/cannot flow | Can flow/not rigid | Can flow/not rigid |
| Compressibility | negligible | compressible | Highly compressible |
(b) (i) Rigidity: It is the propensity of a substance to continue to remain in its shape when treated with an external force.
(ii) Compressibility: It is the attribute of the particles to contract its intermolecular space when exposed to an external force thereby escalating its density.
(iii) Fluidity: It is the ability of a substance to flow or move about freely.
(iv) Filling the gas container: The particles in a container take its shape as they randomly vibrate in all possible directions.
(v) Shape: It is the definite structure of an object within an external boundary
(vi) Kinetic energy: Motion allows particles to possess energy which is referred to as kinetic energy. The increasing order of kinetic energy possessed by various states of matter are:
Solids < Liquids < Gases
Mathematically, it can be expressed as K.E =1/2mv2, where ‘m’ is the mass and ‘v’ is the velocity of the particle.
(vii) Density: It is the mass of a unit volume of a substance. It is expressed as:
d = M/V, where ‘d’ is the density, ‘M’ is the mass and ‘V’ is the volume of the substance
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.
c) A wooden table should be called a solid.
d) We can easily move our hand in the air but to do the same through a solid block of wood we need a karate expert
Answer - 6 : -
a) Kinetic energy possessed by gas particles is very high which allows them to randomly move
across all directions when contained, hence the particles fills the gas vessel entirely.
b) Gas molecules possess high kinetic energy, due to which they are under constant motion inside
the container in random directions which causes them to hit the walls of the container and hence create vibrations. These collisions with the walls of the container generate pressure.
c) A wooden table should be called a solid as it possesses all the properties of a solid such as:
- Definite size and shape
- Intermolecular attraction between closely packed particles.
- It is rigid and cannot be compressed
d) Molecules in gases are loosely packed as compared to solid molecules which are densely packed.
Hence we are easily able to break the force of attraction when we move our hand through air but find it difficult to break through a solid (because of greater forces of attraction between molecules) which a karate expert is able to smash with the application of a lot of force.
Question - 7 : - Liquids generally have a lower density than solids. But you must have observed that ice floats on water. Find out why.
Answer - 7 : -
Density of ice is less than the density of water. The low density of ice can be attributed to the small pores it has which allows it to trap air hence ice floats on water.
Question - 8 : - Convert the following temperature to Celsius scale:
a. 300K b. 573K
Answer - 8 : -
a. 0°C=273K
300K= (300-273)°C = 27°C
b. 573K= (573-273)°C = 300°C
Question - 9 : - 2. What is the physical state of water at:
a. 250°C b. 100°C ?
Answer - 9 : -
(a) At 250°C – Gaseous state since it is beyond its boiling point.
(b) At 100°C – It is at the transition state as the water is at its boiling point. Hence it would be present in both liquid and gaseous state.
Question - 10 : - For any substance, why does the temperature remain constant during the change of state?
Answer - 10 : - It is due to the latent heat as the heat supplied to increase the temperature of the substance is used up to transform the state of matter of the substance hence the temperature stays constant.