Matter in our surrounding Worksheet-5

Matter in our surrounding Worksheet-5

 

  1. Why does steam produce more severe burns on the skin as compared to boiling water?

 

  1. Carbon dioxide gas is heavier than both nitrogen and oxygen. Why it does not form lower layer in the atmosphere?

 

  1. Ammonia and hydrogen chloride gases are both pungent smelling in nature. These are released from the two opposite corners in a room. Which gas will first reach a person sitting in the centre of the room?

 

  1. Solids are normally not compressible. Why a sponge can be readily pressed?

 

  1. Why is it not proper to regard the gaseous state of ammonia as vapours?

 

  1. What happens to the heat energy which is supplied to the solid once it has started melting?

 

  1. Kelvin scale of temperature is regarded better than the Celsius scale. Assign reason.

 

  1. Gases can be compressed but solids cannot. Explain.

 

  1. A rubber band changes its shape when stretched. Can it be regarded as solid ?

 

  1. Name one property which is shown by naphthalene and not by sodium chloride.

 

Answer:

  1. When water is converted into steam at 100°C (373 K) it absorbs latent heat of vaporisation. Therefore, steam has more energy than water at 100°C. When steam condenses, it releases more energy. Because of this, steam produces more severe burns on the skin as compared to boiling water.

 

  1. The rate of diffusion of gas is not affected by gravity. So Carbon dioxide (CO2) remains uniformly mixed in air. Therefore, the gas does not form the lower layer in the atmosphere.

 

  1. Rate of diffusion of gas varies inversely with mass of gas molecules. The particles of the lighter gas will diffuse faster as compared to those of heavier gas. Out of the two gases, ammonia is lighter than hydrogen chloride gas. (Molecular mass of NH3 = 17u) Molecular mass of HCl = 36.5u Therefore, smell of ammonia will reach the person first.

 

  1. A sponge made up of a material, which has large number of fine pores in which air remains filled. When the sponge is pressed, the air from the pores escapes and vacant spaces are left. Therefore, the sponge can be readily on applying pressure. Whereas in solids particles are compactly packed, thus it cannot be readily compressed.

 

  1. The gaseous state of a substance can be regarded as vapour only when it exists in liquid state at room temperature. Since ammonia is a gas at room temperature, its gaseous state cannot be regarded as vapours.

 

  1. Once the solid has started melting heat energy absorbed is consumed in bringing about the change in state from solid to liquid (overcoming the force of attraction between the particles of solids). The heat absorbed is known as latent heat of fusion.

 

  1. In the Celsius scale of temperature we often come across a negative sign for the temperature (e.g.,–8-5°C). In the Kelvin scale sign of temperature is always positive hence, it is a better scale.

 

  1. In gases, interparticle spaces are quite large. On applying pressure, these spaces decrease and the molecules of gas come closer. As a result, the gases can be compressed. Whereas in solids, particles are compactly packed leaving negligible interparticle space thus solids cannot be compressed.

 

  1. Rubber is a solid. It has elastic property due to which it undergoes change in shape when pressure is applied and regains its original shape when pressure is released.

 

  1. Naphthalene undergoes sublimation upon heating i.e. it directly changes into vapours. Whereas Sodium chloride (common salt) does not undergo sublimation. It melts on strong heating.