Q1 Why gases fill their container completely?
Q2 At what temperature does solid ice and liquid water co-exist together?
Q3 Define latent heat of fusion and boiling point of a liquid
Q4 Convert the following temperature into Kelvin
(i) 120 o C (ii) -15 o C
Q5 Suggest an activity to show that air contains water vapour?
Q6 When you put Acetone on your palm you will cold, Why?
Q7 Water kept in earthen pot becomes cool during summer, explain the phenomenon behind this?
Q8 When a person suffering from fever, doctor advise him to put a cold wet cloth on forehead. Why?
Q9 Compare the properties of solid, liquid and gases on the basis of following:-
Density, Kinetic energy of particle, inter-particle space, force of attraction between particles.
Q10 What is the effect of the following on the rate of diffusion?
Temperature and Density of liquid
Q11 Which gas is called dry ice and why?
Q12 Liquids like alcohol and ether are kept in cool places. Why?
Q13 Define melting point. What does melting point of a substance indicate?
Q14 Name the factors affecting evaporation also explain each of them.
Q15 After morning exercise, you feel cold. Why?
Answers
Answer:
Explanation:
1) Because Gases are loosely packed.So,it will be spread over completely in a container.
2)273.16 K or 0.01°C
3)The amount of heat energy required to change 1kg of a solid into liquid at atmospheric pressure at its melting point is called the latent heat of fusion.
The temperature at which a liquid starts boiling is called its boiling point. The boiling point of water is 1000C or 373K ( 273 + 100).
4) K=°C+273
So, (i)120+273=393 K
(ii)-15+273=273-15=258 K
7)Evaporation.Because some water molecules inside the pot will escape through the pores and reach outside surface of the pot.That water will absorb the heat of the internal water also. Evaporation always causes cooling.
11)Carbon di oxide is freezed at high pressure to form dry ice.
13)The temperature at which a solid melts is called its melting point. The melting point of ice is 00C or 273 K.
14)The rate of evaporation depends upon surface area, temperature, humidity and wind speed.
⇒ Increase in the surface area increases the rate of evaporation.
⇒ Increase in temperature increases the rate of evaporation.
⇒ Increase in humidity decreases the rate of evaporation.
⇒Increase in wind speed increases the rate of evaporation.
Sorry,friend I know answers for only these questions.I don't know for others.
Answer:-
Q5. Take out a bottle of water(cold) from the refrigerator and place it on the table. You will see small drops of water appearing on the outer surface of the bottle. This is because water vapour present in the air condenses and forms small drops of water. This activity proves that air contains water vapour.
Q6. When we put some acetone or petrol or perfume on our palm, it evaporates. During evaporation, particles of the liquid absorb energy from the surface of the palm to compensate for the loss of energy, making the surroundings cool. The acetone, petrol or perfume take this latent heat of vaporisation from our palm.
Q8. Because the water evaporates and absorb the heat from the body that cause cooling and lowering the body temperature. that is why the doctor advices to put strips of wet cloth on the forehead of a person having fever.
Q9. density:- solids have highest density, liquids have less density than solids and gases have the least density.
kinetic energy of particles:- solids have very less kinetic energy, liquids have medium kinetic energy and gases have very high kinetic energy.
inter-particle space:- The inter-particle space is minimum in solid, Liquid has more inter-particle space than solid and gases have maximum inter-particle space.
force of attraction between particles:- Solids have highest force of attraction between particles, liquids have lesser force of attraction between them and gases have negligible force of attraction between them.
Q10. temperature:- Higher temperatures increase the energy and therefore the movement of the molecules, increasing the rate of diffusion.
Density of liquid:- As the density of a liquid increases, the rate of diffusion decreases.
Q12. it is because both of them have extremely low flash points (the temperature where they become a gas) and extremely low ignition points ( the temperature where they burn). They are expected to evaporate at a fast rate in case temperature is at room temperature and they may explode if the temperature is increased . Therefore, the temperature has to be lowered or they are to be kept in cool place.
Q15. When we perform various exercise, we generally sweat. Sweat formed on the skin evaporates into the atmosphere by absorbing heat energy from our body. As evaporation causes cooling effect. Hence our body temperature reduces and we feel cool.
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