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We first need to calculate the amount of heat energy required to raise the temperature of water to its boiling point(100°C) using the formula Q= mc? where Q is the amount of heat energy required, m is the mass of the sample of water, c is the specific heat capacity of water and ? is the change in temperature. 

Q= (20.0)(0.999043976)(100-25) 

= 1.49*10³ cal .

We now need to calculate the amount of heat energy required to convert the sample of water to steam at its boiling point using the formula Q= mL where Q is the amount of heat energy required, m is the mass of the sample of water and L is the latent heat of vaporization of water. 

Q= (20.0)(540) 

 = 1.08*10? cal 

so,total heat energy required= (1.49+10.8)*10^4 cal