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ICSE Class 8 Answered

GIVE REASONS 1)dry ice is actually CO2 gas. 2)solids do not take the shape of the containerthay are kept in. 3)steam causes more severe burns than boiling water does. 4)snow on the top of mountains does not melt all at once. 5)drink are cooled more effectively by storing them in ice pieces rather than in ice cold water at 0 degree centrigate 6)change of state takes place at a fixed temperature    
Asked by nathsantanukumar | 22 Mar, 2018, 03:42: PM
answered-by-expert Expert Answer
CO2 gas is compressed and refregirated to get liquid state. Then this liquid state CO2 is further cooled to get solid state CO2. This solid state CO2 is dry ice.
Very stron intermoleculer force exist in solid state between molecules, so solid state object has its own shape and it does not take shape of container.
 
Steam contains the absorbed latent heat of vaporaisation (2260 kJ/kg). Hence it contains more heat energy compared to the 100°C water.
 
Ice, which is solid state of water, requires 336 kJ/kg of heat energy (latent heat of fusion) to convert from 0°C ice to 0°C water.
Hence the snow on the mountain does not melt at once.
 
drinks are cooled more effectively by keeping ice pieces, because when ice melts it absorbs 336 kJ/kg heat energy from liquid. Hence liquid becomes more cooled
 
Change of state takes place fixed temperature, because the absorbed energy is not utilized to increase the kinetic energy of molecules but to break the chemical bond in order to increase the potential energy. Since kinetic energy of molecules is not changed during the change of state, temperature remains constant.

Answered by Thiyagarajan K | 24 Mar, 2018, 12:02: PM

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