This is my homework page and I will do my homework regularly.
DATE 04/April/2016
Q - Why do we observe that level of water does not change even after the dissolving of salt in it?
A - The molecules of water have space between them ,the level of water does not increase because the molecules of salt fit between them and do not increase the level of the water.
DATE 05/April/2016
Properties of particles
- The particles of matter are very small
- The particles of matter are continuously moving means they have kinetic energy.
- The particles of matter have space between them.
DATE 07/April/2016
Extra questions.
Q1- Why is a diver able to cut through water easily but not through a solid block?
A1- A diver can cut through water because the intermolecular force is less and intermolecular space is high in water than that of solids.
In case of the block the intermolecular space is less and the intermolecular force is very high making it difficult for the diver to make a dive.
Q2- How does the smell of hot food reaches us a several metres away but not of cold food?
A2- Hot food has high temperature and hence high kinetic energy thus giving it's particles a long range whereas cold food has comparatively low temperature hence its particles cannot travel a long distance.
Q3- Why do solids have a fixed shape?
A3- Solids have a fixed shape because they have high interparticle force and low interparticle force giving them a strong and rigid structure.
DATE 10/April/2016
DATE 10/April/2016
Homework
- Latent heat of vaporisation
The Latent heat of vaporisation is the amount of heat energy required to convert one kg of a liquid to gas at atmospheric pressure at it's boiling point.
- Latent heat of fusion
Latent heat of fusion is the amount of heat energy required to convert one kg of solid into liquid at it's melting point.
Evaporation
Evaporation is a process in which particles from the surface gain enough energy to overcome the force of attraction of the liquid and convert to the
gaseous state.
Factors affecting rate of evaporation
gaseous state.
Factors affecting rate of evaporation
The following are some factors which affect the rate of evaporation:-
(1) Surface area : Surface area is directly proportional to evaporation , an increase in surface area means increase in evaporation.
(2) Temperature : Temperature is also directly proportional to evaporation because temperature provides enough kinetic energy to the particles to get converted into the vapour state.
(3) Humidity : Humidity is inversely proportional to evaporation because if Humidity is high then the air cannot hold more water vapours and thus decreases the rate of evaporation.
(4) Wind speed : Wind speed is directly proportional to evaporation because it helps in carrying away the water vapours making the substance dry.
DATE 18/April/2016
EXERCISES
1. Convert the following temperatures to Celsius scale.
(a) 300 K
► 300 K = (300 - 273) °C
= 27 °C
(b) 573 K
► 573 K = (573 - 273) °C
= 300 °C
2. Convert the following temperatures to Kelvin scale.
(a) 25°C
►25 °C = (25 + 273) K
= 298 K
(b) 373°C
► 373 °C = (373 + 273) K
= 646 K
3. Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Answer
(a) Naphthalene balls disappear with time without leaving any solid because they undergo sublimation ( directly convert from solid to gas.)
(b) The perfume is a liquid whose rate of vaporisation is very high and all of it's particles get evaporated and reach us a several metres away.
4. Arrange the following substances in increasing order of forces of attraction between particles-- water, sugar, oxygen.
Answer
5. What is the physical state of water at-
(a) 25°C
► Liquid State
(b) 0°C
► Solid State
(c) 100°C
► Gaseous State
6. Give two reasons to justify-
(a) water at room temperature is a liquid.
(b) an iron almirah is a solid at room temperature.
Answer
(a) Water at room temperature is a liquid because it has fluidity also it has no shape but has a fixed volume that is, it occupies the shape of the container in which it is kept.
(b) An iron almirah is a solid at room temperature because it is rigid and has a fixed shape.
7. Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer
Ice at 273 K has less energy than water becaause water possesses the additional latent heat of fusion. Hence, at 273 K, ice is more effective in cooling than water.
8. What produces more severe burns, boiling water or steam?
Answer
Steam has more energy than boiling water. It possesses the additional latent heat of vaporization. Therefore, burns produced by steam are more severe than those produced by boiling water.
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