for bs chemical engineering study

2. Latent heat
Latent heat (also known as latent
energy or heat of transformation) is energy
released or absorbed, in change of phase is
not externally manifested by any rise or fall
of temperature.

3. Types
•latent heat of fusion(Melting)
•Latent heat of vaporization(Boiling)
•They describe the direction of flow of
energy when changing from one phase
to other : solid to liquid and liquid to
gas.

6. State

7. problem
Calculate the amount of heat added to 1
gram gold to change phase from solid to
liquid. The heat of fusion for gold is 64.5 x
103 J/kg.
Data :
Mass (m) = 1 gram = 1 x 10-3 kg
Heat of fusion (LF) = 64.5 x 103 J/kg
find: Heat (Q)
Solution :
Q = m LF
Q = (1 x 10-3 kg)(64.5 x 103 J/kg)
Q = 64.5 Joule

9. Problem
Determine the amount of heat absorbed by 1 kg
water to change phase from liquid to vapor
(steam). Heat of vaporization for water = 2256 x
103 J/kg
Data :
Mass (m) = 1 kg
Heat of vaporization (LV) = 2256 x 103 J/kg
find: Heat (Q)
Solution :
Q = m LV
Q = (1 kg)(2256 x 103 J/kg)
Q = 2256 x 10

10. Enthalpy
Enthalpy is the heat content of a
system. The enthalpy change of a
reaction is equivalent to the amount of
energy lost or gained during the
reaction.
Enthalpy is equal to the internal energy.

11. Formula
H=E+PV
H=enthalpy
E=internal energy
P=pressure
V=volume

12. Change in enthalpy
Enthalpy is a state function . It is
measured in joules. It is not possible
to measure the enthalpy of a system
in a given state . However , change in
enthalpy(∆H) can be measured for a
change in the state of system . A
change in enthalpy is given below:
∆H= ∆E+ ∆(PV)
∆H= ∆E+V ∆P+P ∆V
Since gas is kept constant, ∆P=0
Hence, ∆H= ∆E+P ∆v

13. In case of liquid and solid?
The change in state do not cause
significant volume change i.e. ∆V=0.
For such process, ∆H and ∆P are
approximately the same i.e. ∆H ≈
∆E.
According to first law of
thermodynamics :
∆E= q+w

14. Is enthalpy positive or negative?
The change in enthalpy in an exothermic reaction
is negative, since overall heat is lost (
"exo"thermic means that heat is leaving).
The opposite of this would be a positive change
in enthalpy during an endothermic reaction.