Question

7. Calculate the amount of energy required heat 100.g to the following: a. H2O(s) changes to H2O(l) at 0°C b. H2O(l) changes to H20 (s) at 0°C c. H2O(l) at 10°C changes to H2O(l) at 20°C​

Answer 1

a=b=33400 J

c=4180 J

Further explanation

Heat can be calculated using the formula:  

Q = mc∆T  

Q = heat, J  

m = mass, g  

c = specific heat, joules / g ° C  

∆T = temperature difference, ° C / K  

The heat to change the phase can be formulated :

Q = mLf (melting/freezing)

Q = mLv (vaporization/condensation)

Lf=latent heat of fusion

Lv=latent heat of vaporization

The heat of fusion for water at 0 °C : 334 J/g and the heat of vaporization at 100 °C : 2,230J/g

a. melting

$\tt Q=100.334=33400~J$

b. freezing

$\tt Q=100.334=33400~J$

c.raise the temperature(c water = 4.18 J/g C)

$\tt Q=100\times 4.18\times (20-10)=4180~J$