How much energy is released when 34.2 g of water freezes?

Solution 59P

Step 1:

Amount of water = 34.2 g

Energy released when 34.2 g of water freezes = ?

Heat must be removed from the water to cause it to freeze and become ice.

The amount of heat released by freezing 1 mole of water is 6.02 kJ/mol.

Formula to calculate the heat required :

 q = mHf

where, q = heat in kJ,

m = mass(in grams),

Hf = heat of fusion

We have Hf in terms of moles, but the mass is given in grams. So let’s find the number of moles for the given amount of water.

So, let’s find number of moles :

        Number of moles(m) =  

Molar mass of water = 18.01 g/mol

        Therefore, number of moles =

                                          = 1.89 moles.

So, number of moles in 34.2 g of water is 1.89 moles.