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Three
States of Matter
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Scientific
Reasons
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| Q1) Steam produces severe burns, then boiling water, although both have same temperature. | ||
| Both steam and boiling water have the same temperature i.e. 100 oC. But heat content of steam is greater than the boiling water because latent heat of steam is 2.26 x 105 J/kg .That’s why steam produces severe burn as compared to boiling water. | ||
| Q2) evaporation causes cooling. | ||
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Temperature is the measurement of average kinetic energy of molecules. As liquid evaporates, high kinetic energy molecules escape from the liquid and lowers the average kinetic energy molecules remain in the liquid. Due to this reason temperature falls down |
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Q3) In mountain areas food takes longer time to cook. |
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Boiling point of a liquid depends on the outer atmospheric pressure.At normal atmospheric pressure boiling point of water is 100 0C. on mountain areas such as Quetta and Swat, atmospheric pressure is below 760 torr. Due to this reason B.P of water decreases and food takes longer time to cook. |
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Q4) Glycerin distilled at 290 0C but it decompose at this temperature, how would you distilled it? |
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| At 760 torr, B.P of glycerin is 290 0C but at 290 0C temperature glycerine evaporates and it become difficult to distill it. In order to overcome this difficulty it is distilled at 50 torr . At 50 torr it’s B.P decreases to 210 0C. At 210 0C it does not decompose and distiledl easily. | ||
| Q5) Evaporation of a liquid is accelerated on heating? | ||
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Rate of evaporation increases with the increase in temperature because on heating kinetic energy of molecules becomes high enough to overcome intermolecular forces of attraction. Thus number of molecules leaving the liquid surface is increased. So the rate of evaporation increases on heating |
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| Q6) Falling drop of liquid is spherical. | ||
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Falling drop of a liquid is always spherical in shape due to surface tension. The inward forces on the surface molecules of the liquid droplet tend to cause the surface to volume ratio as small as possible. Since surface to volume ratio is minimum for the spherical shape that’s why falling drop of a liquid is spherical. |
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| Q7) Under similar conditions surface tension of water is higher than the surface tension of ether. | ||
| Surface tension depends upon the strength of intermolecular forces of attraction. Water has higher surface tension due to polar nature of its molecules. In water there exist hydrogen bond as compared to ether, which is non-polar and has no hydrogen bond. We know that hydrogen bond increases intermolecular attraction. Consequently water has high surface tension. | ||