Question

give reason
a) The density of water is maximum at 4°C
b)The burn caused by steam (at 100°C) is more painful than burn caused by water(at 100°C)​

Answer 1

Answer:a) The maximum density of water occurs at 4 °C because, at this temperature two opposing effects are in balance. Explanation: In ice, the water molecules are in a crystal lattice that has a lot of empty space. When the ice melts to liquid water, the structure collapses and the density of the liquid increases.b) Steam will produce  more severe burns than boiling of water because steam has more heat energy than water due to its latent heat of vaporisation and additionally latent heat of condensation. Steam and boiling water can exist at varing temperature but it is only correct to assume here that both are at same temperature.

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Answer 2

a) Because there is a phenomenon which water has, and it is called "anomalous expansion of water". When cooling water, the water molecules slow down and the density increases. At 4°C, the clusters start forming. The molecules are slowing down but the formation of clusters make them be further apart. That is why density of water is maximum at 4°C.

b) Because steam has more latent heat of vaporization. When steam falls on the skin and condenses to produce water, it gives out more heat than boiling water at the same temperature because of the latent heat. (precisely 22.5×105 KJ more than boiling water). That is why burn caused by steam is more painful than burn caused by boiling water.