Chemistry 9 (Thermodynamics)

Front 1

Thermodynamics

Back 1

Transfer of energy from one form to another

Front 2

"In" to system/"Out" of system

Back 2

In: +q
Out: -q

Front 3

Physical Thermodynamic Equations (2)

Back 3

(1) E = q + w
(2) W = -P*V

Front 4

Compressed Gases ____
Expanding Gases _____

Back 4

WARM!
COOL!

Front 5

Isobaric

Back 5

- Constant P
- Area under the boxed curve is work done

Front 6

Isochoric

Back 6

- Constant V
- No work is done and the total energy is equal to q.
- Piston didn't move!

Front 7

Isothermal

Back 7

- Constant T
- Heat is transferred freely between system and the environment
- E = 0, q = -w

Front 8

Adiabatic

Back 8

- no heat is transferred between the system and the environment
- all energy is work
- q = 0 (no heat), so E = w.
- Also known as a perfectly insulated system

Front 9

Second Law of Thermodynamics

Back 9

- The important one...two ways to interpret it:
- Disorder increases in a spontaneous process
- All processes run in direction leading to maximum disorder

Front 10

Entropy

Back 10

ΔS = S(prod) - S(reactants)

Increase in disorder is +++
Decrease in disorder is ----

Front 11

Enthalpy

Back 11

ΔH = H(prod) - H(reactants)

- Measure of heat released or absorbed at a constant pressure. Always the same for a rxn.
- "Breaking Up Is Hard To Do"
- If energy is required, ΔH +++
- If energy is released, ΔH -----

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Exothermic

Back 12

- Energy Released
- Typically when we form bonds
- Products in a lower state of energy than the reactants
- NEGATIVE NEGATIVE NEGATIVE ΔH!

Front 13

Endothermic

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- Energy Needed
- Typically when we break bonds
- Reactants in a lower energy state than products
- POSITIVE ΔH! POSITIVE ΔH!

Front 14

Three Ways We Can Calculate ΔHrxn

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- ΔHrxn is basically just the enthalpy change of a reaction
- Heat of Formation
- Hess's Law of Summation
- Bond Energy

Front 15

Heat of Formation (ΔHf)

Back 15

- Amount of energy required to make one mol of a compound from its constituent elements in their natural state (where ΔHf = 0)

ΔHrxn = (n*Products) - (n*Reactants)

Conclusions:
(+) ΔHf, making compound from element requires heat (endo)
(-) ΔHf, making compound from element gives off heat (exo)

Front 16

What are the Standard State parameters used for Thermodynamics?

Back 16

- 25°C, 298K, 1M
- This is called ΔH°.

Front 17

Hess's Law of Summation

Back 17

- Sum of the ΔH in individual steps will equal the overall ΔH.
- Notes: if reaction is reversed, sign reversed too, and if multiplied by a constant to balance equation, ΔH must be multiplied too

Front 18

Summation of Bond Enthalpies

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- ΔH can be viewed as energy stored in chemical bonds
- "Breaking Up Is Hard To Do"

ΔHrxn = (BDE broken) - (BDE formed)

Front 19

Gibbs Free Energy

Back 19

- Energy available to do useful work in a chemical reaction


ΔG = ΔH - TΔS

Front 20

Thermodynamics and Equilibrium

Back 20

ΔG° = -RTln(Keq)

ΔG = ΔG° + RTln(Keq)