Question Answers of matter in our surrounding

Q1. How melting point of a substance indicates the strength of of its intermolecular forces of attraction
Ans: More strong is the force of attraction more energy is required to break 20 forces of a fraction hence the substance which has high melting point indicates that its particles are tightly packed.

Q2. Suggest a method to liquefy gases
Ans: By applying pressure and reducing temperature.

Q3. Define latent heat of vaporization
Ans: latent heat of vaporization is defined as the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.

Q4.Define latent heat of fusion

Ans:It is defined as the heat required to change 1 kg of solid to liquid at its melting point.

Q5. When a solid melts its temperature remains the same so where does the heat energy go?
Ans: During the experiment of melting the temperature of the system does not change even after the melting point is reached till all the ice melts. This happens even though we continue to apply heat . This heat gets used up in changing the state by overcoming the forces of attraction between the particles. As the heat energy is absorbed by ice, Without showing any rise in temperature it is considered that it gets hidden into the contents of the beaker I known as latent heat of fusion.

Q6. Why sometime temperature does not rise even when heat is supplied?

Ans: During the change of state heat is absorbed but the heat is used up in changing the state by overcoming the forces of attraction between the particle. Thus there is no change in temperature.

Q7. Which gas is called dry ice and why

Ans: Solid carbon dioxide is called dry ice as it's directly converted to to gaseous state on decrease of pressure to 1 atmosphere without changing into liquid state. Due to this fact solid carbon dioxide is also known as dry ice.

Q8 Give reason for the following;
(a) naphthalene ball disappear which time without leaving any solid.
Ans: By absorbing heat energy from the surrounding naphthalene balls directly e gets converted into vapour and disappear with time without leaving any solid.

(b) we can get the smell of perfume sitting several Metres away
Ans: The molecules of perfume Elante near diffuse in all directions as they are volatile and therefore we can smell The Perfume sitting several metres away.

Q9. Why are we able to SIP hot tea or milk faster from a saucer rather than a cup?
Ans; As we know that the surface area is directly proportional to the rate of evaporation .Thus the milk in saucer cools at faster rate as compared to cup.

Q10. Why does a desert cooler cool better on hot and dry day?
Ans: Desert cooler cool better on a hot dry day because the higher temperature on the hot day increases the rate of evaporation of water from the maths and the dryness of hair indicates low humidity which also increases the rate of evaporation full stophands due to increased rate of evaporation a desert cooler cool better on a hot dry day.

Q11. Suggest method to liquefy gases?

Ans; Gases can be liquefied by applying pressure and reducing temperature.

Q12. Why sometimes temperature does not rise even when heat is supplied?

Ans: during the change of state heat is absorbed but this heat it gets used up in changing the state of matter by overcoming the forces of attraction present between the particles. Hence there is no change in temperature although heat is being absorbed constantly. 

Q13 What produces more severe burns ,boiling water or steam?

Ans: Steam produces more severe burns because it has high latent heat of vaporization.Thus,1 kg of steam at 100⁰c contains 2260 kJ of more heat energy than 1 kg of water  at 100⁰c.It is enormous amount of hidden heat in steam which causes more severe burns.

Q14.Define evaporation.write the factors affecting rate of evaporation.

Ans: 

Evaporation is the process in which a liquid state of matter (water)  is converted into a gaseous state of matter (vapour) at all temperatures without reaching at its boiling point.

Factors That Affect the Evaporation

• Temperature: As the temperature increases, the rate of evaporation also increases. Temperature and rate of evaporation are proportional to each other
• Surface area: As the surface area increases, the rate of evaporation increases. The surface area and rate of evaporation are proportional to each other.
• Humidity: The rate of evaporation decreases with an increase in humidity. Humidity and the rate of evaporation are inversely proportional to each other.
• Wind speed: Increase in wind speed results in increased evaporation. Wind speed and rate of evaporation are proportional to each other.

Q15.(a) Evaporation causes cooling.

Ans:Evaporation Causes Cooling

Evaporation causes cooling is the general process. The principle involved here is the matter must either gain or lose energy to change its state. Here molecules move from liquid to gaseous state and so it needs potential energy and kinetic energy. Due to this energy transfer occurs in the surroundings as well and this is transferred from substance to surroundings or vice versa. The change in temperature till the evaporation process will lead to cooling. Hence evaporation causes cooling effect. When a liquid evaporates, the particles of the liquid absorb energy from the surroundings to compensate for the loss of energy during evaporation. Since evaporation causes cooling, this makes the surroundings cool.

Q16.Why are we able to sip hot tea or milk faster from saucer rather than from a cup?

Ans: The rate of evaporation increases with increase in surface area.The surface area of saucer is more than that of the cup, hence the rate of evaporation is faster in saucer and the hot te or milk cools faster in saucer.So, we are able to sip hot te or milk faster from saucer rather than from cup.

Q17.Define sublimation 

Ans: It is a process in which the solid is directly changes to gas.

Eg ; camphor, carbon dioxide etc