The latent heat of fusion of ice is 80 calories per gram. This means that if we have 20 grams of ice to be melted from solid to liquid at the freezing point of 0 degrees C, we find the total heat requirement by:
Q = m(Lf) = (20 g)(80 cal/g) = 1600 calories
So the total heat requirement is 1600 calories.
Answer is (A)
Pottasium and Sodium salts are soluble in water. When these soaps are added to hard water. Hard water contains calcium or magnesium ions and they form Magnesium or Calcuim salts. These salts of magnesium and calcium precipitates out and are insoluble in water. This precipitation is called as dirt (the exact word for dirt is not acceptable here). This process is considered as the disadvantage of soap as well as using hard water.
2NH₃(g) + CO₂(g) → CO(NH₂)₂(s) + H₂O(l)
is the balanced equation for the synthesis of urea.
It would be an physical change ; if you melt butter the butter goes from a solid to a liquid so therefore the physical state is changed.