Change of state in mixing
Suppose you want to drink cool water on a hot day, but you only have some hot water. So you put in some ice cubes to cool down the water. Let's calculate how much ice is needed to cool down the water to a given temperature.
You are given 200 g of water at 90
. How much ice at 0 is
needed to cool down the water to 10 .
Suppose no heat is lost to the surroundings,
Therefore 179 g of ice is needed to cool down the water.
In following animation, we will calculate the temperature of water obtained by mixing ice and hot water.
We can use a domestic electric boiler to boil some water and ice mixture. From the time required, we can estimate the specific latent of fusion of water. See the following activity.
Have you ever seen how people prepare cold Horlicks drink
in a restaurant? They first use a small amount of hot water to dissolve
the Horlicks powder completely, and then add some ice cubes to the drink.
The ice cubes absorbs latent heat of fusion as they melt, thus cooling
down the drink quickly.