Rucete ✏ Chemistry In a Nutshell
1. Energy
Energy is the capacity to do work.
Two major forms:
Thermal energy: energy due to particle motion (heat).
Chemical energy: stored in chemical bonds.
Unit: kilojoules (kJ)
2. Temperature vs. Heat
Temperature: average kinetic energy of particles in a substance.
Heat: thermal energy transferred due to temperature difference.
3. System vs. Surroundings
System: the part of the universe being studied.
Open system: exchanges mass and energy.
Closed system: exchanges energy only.
Isolated system: no exchange of mass or energy.
Surroundings: everything outside the system.
4. State Functions
Properties that depend only on the current state, not the path (e.g., ΔH, ΔS, ΔG).
Examples: pressure, volume, temperature, enthalpy.
5. Standard State
Conditions: 1 atm, 1 M concentration, 298 K (25°C).
Standard enthalpy (ΔH°), entropy (ΔS°), and free energy (ΔG°) values are measured under these.
6. Laws of Thermodynamics
First Law:
Energy cannot be created or destroyed, only transformed.
ΔE = q + w (change in internal energy = heat + work)
Second Law:
In any spontaneous process, entropy (ΔS) increases.
Systems tend toward disorder.
Third Law:
Entropy of a perfect crystal at 0 K = 0.
7. Enthalpy (ΔH)
Measure of heat at constant pressure.
Exothermic (ΔH < 0): releases heat.
Endothermic (ΔH > 0): absorbs heat.
8. Spontaneity
A reaction is spontaneous if it occurs without external input.
Driven by enthalpy (ΔH) and entropy (ΔS).
9. Hess’s Law
The total enthalpy change is the same, regardless of how the reaction occurs.
ΔH (overall) = sum of ΔH for each step.
10. Heat of Formation
Heat change when one mole of a compound forms from its elements.
11. Specific Heat and Heat Capacity
Specific heat (c): energy needed to raise 1 g of a substance by 1°C.
Heat capacity (C): energy needed to raise a given mass by 1°C.
Formulas:
12. Calorimetry
Measurement of heat flow in a system.
Used to determine:
Heat of neutralization
Heat of dilution
13. Entropy (ΔS)
Measure of randomness/disorder.
More gas molecules = higher entropy.
ΔS increases with temperature, volume, and number of particles.
14. Gibbs Free Energy (ΔG)
Combines enthalpy and entropy to predict spontaneity.
Spontaneity:
ΔG < 0 → spontaneous
ΔG > 0 → non-spontaneous
ΔG = 0 → equilibrium
15. Energy Diagrams
Activation energy (Ea): barrier that must be overcome for a reaction.
ΔH is the difference between products and reactants.
Exothermic: products lower than reactants.
Endothermic: products higher than reactants.