A food product is being frozen in a system capable of removing 6000 kJ of thermal energy. The product has a specifi c heat of 4 kJ/(kg C) above the freezing temperature of 2 C, the latent heat of fusion equals 275 kJ/kg, and the frozen product has a specifi c heat of 2.5 kJ/(kg C) below 2 C. If 10 kg of product enters the system at 10C, determine the exit temperature of the product..

Answer : The exit temperature of the product is,

Explanation :

Total heat = Heat lost by liquid + Latent heat of fusion + Heat lost by frozen

where,

Q =  Total heat = 6000 kJ

m = mass of product = 15 kg

= specific heat of liquid =

= latent heat of fusion =

= specific heat of frozen =

= initial temperature of liquid =

= final temperature of liquid =

= initial temperature of frozen = ?

= final temperature of frozen =

Now put all the given value in the above expression, we get:

Thus, the exit temperature of the product is,

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.