Anomalous Expansion of Water
The way substances generally react to heat is that they expand when heated as the density decreases and vice versa takes place then they are cooled. This is not the case with water. The general tendency of cold water remains unchanged until 4oC. The density of water gradually increases as you cool it. When you reach 4oC, its density reaches a maximum. When you cool water further to make ice (i.e. 0oC), it expands with a further drop in temperature; meaning the density of water decrease when you cool it form 4oC to 0oC.
The effect of this expansion of water is that the coldest water is always present on the surface which is why ice is seen on the surface of water. Since water at 4oC is the heavest, this water settles on the bottom of the water body and the lightest i.e. the coldest layer accumulates on the top layer. This is why the top of the water is always the first to freeze. Since ice and water are both bad conductors of heat, this top layer of ice insulates the rest of the water body from the cold thereby protecting all the life in the water body.
The way substances generally react to heat is that they expand when heated as the density decreases and vice versa takes place then they are cooled. This is not the case with water. The general tendency of cold water remains unchanged until 4oC. The density of water gradually increases as you cool it. When you reach 4oC, its density reaches a maximum. When you cool water further to make ice (i.e. 0oC), it expands with a further drop in temperature; meaning the density of water decrease when you cool it form 4oC to 0oC.
The effect of this expansion of water is that the coldest water is always present on the surface which is why ice is seen on the surface of water. Since water at 4oC is the heavest, this water settles on the bottom of the water body and the lightest i.e. the coldest layer accumulates on the top layer. This is why the top of the water is always the first to freeze. Since ice and water are both bad conductors of heat, this top layer of ice insulates the rest of the water body from the cold thereby protecting all the life in the water body.
Anomalous Expansion of Water
The way substances generally react to heat is that they expand when heated as the density decreases and vice versa takes place then they are cooled. This is not the case with water. The general tendency of cold water remains unchanged until 4oC. The density of water gradually increases as you cool it. When you reach 4oC, its density reaches a maximum. When you cool water further to make ice (i.e. 0oC), it expands with a further drop in temperature; meaning the density of water decrease when you cool it form 4oC to 0oC.
The effect of this expansion of water is that the coldest water is always present on the surface which is why ice is seen on the surface of water. Since water at 4oC is the heavest, this water settles on the bottom of the water body and the lightest i.e. the coldest layer accumulates on the top layer. This is why the top of the water is always the first to freeze. Since ice and water are both bad conductors of heat, this top layer of ice insulates the rest of the water body from the cold thereby protecting all the life in the water body.
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