# A 2.5kW kettle is left switched on for one minute after the water has started to boil. The kettle contains 100g of water. Would the kettle boil dry?The answer is 33g will remain, have no idea how...

A 2.5kW kettle is left switched on for one minute after the water has started to boil. The kettle contains 100g of water. Would the kettle boil dry?

The answer is 33g will remain, have no idea how to get the answer though.

jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted on

Once the water start to boil if we further heat the water then it will start to evaporate by using the latent heat for vaporization.

The latent heat for vapourization is 2260j J/g for water.

So the kettle kept one minute at boiling temperature.

Energy given from the kettle = 2.5*1000*60 J

= 150000 J

This 150000 J energy was absorbed by water for vaporization. If the mass of water that left as vapour is m

m*2260 = 150000

m = 150000/2260

= 66.37 g

So the water remains in the kettle = 100-66.37 = 33.63 g

Bottle will not dry.

Assumption

Usually when heating water a small amount of water will left as gas before it come to boiling temperature due to the evaporation. Here we have assumed that no evaporation has occurred.

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