how much heat energy is released when 5g of water at 20 degrees changes into ice at 0 degrees C?
take specific heat capacity of water = 4.2j g k and specific latent of fusion of ice as 336

Question

aaronandyson · Answer

@Michele_Laino

michele_laino · Answer

we have to apply this formula:
$$Q = Lm + cm\Delta \theta $$
since, we have subtract heat in order to go from water at 20 degrees to water at 0 degrees, plus we have to subtract heat to go from water at 0 degrees to ice at zero degrees

aaronandyson · Answer

What do you mean..??

michele_laino · Answer

after a substitution, we get:
 $$\Large  Q = Lm + cm\Delta \theta  = \left( {336 \cdot 5} \right) + \left( {4.2 \cdot 5 \cdot 20} \right) = ...Joules$$

aaronandyson · Answer

2100 J?

michele_laino · Answer

here the physical system, namely the  sample of water releases energy to the surrounding environment.
Such energy (heat) is composed by 2 parts or 2 amounts:
1) the energy released during the temperature decresing, from 20 to 0 degrees
2) the energy released by the so formed sample of water at 0 degrees to form a corresponding sample of ice at zero degrees

michele_laino · Answer

I got this: the sample of water releases $2130$ Joules to the surrounding environment