Thermodynamics

- Study of energy changes and flow of energy

- kinetics NOT thermodynamics

- Enthalpy changes, ΔH (heats of reaction)
Heat exchange between system and surroundings
- Nature's trend to randomness or disorder
Entropy

- Internal energy, E
System's total energy
Sum of KE and PE of all particles in system
or for chemical reaction
>> ΔE + energy into system
>> ΔE – energy out of system

Heat q Work w
ΔE = q + w
- Conventions of heat and work

- Energy can neither be created nor destroyed
- It can only be converted from one form to another
> Kinetic ↔ Potential
> Chemical ↔ Electrical
> Electrical ↔ Mechanical
- E is a state function
> ΔE is a change in a state function
> Path independent
> ΔE = q + w

1. Electrical
2. Pressure-volume or PΔV
- w = –PΔV
- Where P = external pressure
- If PΔV only work in chemical system, then

- Reaction done at constant V
ΔV = 0
PΔV = 0, so
ΔE = qV
- Entire energy change due to heat absorbed or lost
- Rarely done, not too useful

More common
Reactions open to atmosphere
Constant P
Enthalpy
H = E + PV
Enthalpy change
ΔH = ΔE + PΔV
Substituting in first law for ΔE gives:
- ΔH = (q – PΔV) + PΔV = qP
- ΔH = qP
>> Heat of reaction at constant pressure pressure on the system is constant
If a pressure in a balloon is greater then 1 atm will push up vise versa —- if you tie off the balloon it is the same as the external pressure !!