thermodynamics
1. Internal Energy, Heat, Work
Internal Energy (U):
Energy stored inside the system due to molecular motion and interactions.
→ It is a state function.
Heat (Q):
Energy transferred because of temperature difference.
→ It is NOT stored in the system.
Work (W):
Energy transferred due to force acting through distance (like expansion).
Physics sign convention:
→
dQ > 0 Heat is given to the system
→
dW > 0 System does work on surroundings
→
dU > 0 Internal energy of system increases
First Law of Thermodynamics (physics form):
dU = dQ − dW
Meaning:
Change in internal energy = heat given to system − work done by system
---
2. Enthalpy (H)
Real life chemistry mostly happens at constant pressure.
So a new quantity was defined:
H=U+P×V
Read as:
Enthalpy equals internal energy plus pressure times volume
At constant pressure:
Change in enthalpy = heat absorbed at constant pressure
So:
Delta H = Q at constant pressure
Meaning:
Enthalpy measures energy of system + energy to make room in surroundings
1. Internal Energy, Heat, Work
Internal Energy (U):
Energy stored inside the system due to molecular motion and interactions.
→ It is a state function.
Heat (Q):
Energy transferred because of temperature difference.
→ It is NOT stored in the system.
Work (W):
Energy transferred due to force acting through distance (like expansion).
Physics sign convention:
→
dQ > 0 Heat is given to the system
→
dW > 0 System does work on surroundings
→
dU > 0 Internal energy of system increases
First Law of Thermodynamics (physics form):
dU = dQ − dW
Meaning:
Change in internal energy = heat given to system − work done by system
---
2. Enthalpy (H)
Real life chemistry mostly happens at constant pressure.
So a new quantity was defined:
H=U+P×V
Read as:
Enthalpy equals internal energy plus pressure times volume
At constant pressure:
Change in enthalpy = heat absorbed at constant pressure
So:
Delta H = Q at constant pressure
Meaning:
Enthalpy measures energy of system + energy to make room in surroundings
