Chemical thermodynamics: Entropy, free energy and equilibrium

Nội dung text: Chemical thermodynamics: Entropy, free energy and equilibrium

1. CHEMICAL THERMODYNAMICS: ENTROPY, FREE ENERGY AND EQUILIBRIUM ..Recapturing 4 April 2025 PH 101: PHYSICAL CHEMISTRY 1
2. Chemical Thermodynamics • Science of interconversion of energy – Heat into other forms of energy – Amount of heat gained/released from a system – Spontaneity of a reaction – Gibbs free energy function – Relationship between Gibbs Free Energy and chemical equilibrium 4 April 2025 PH 101: PHYSICAL CHEMISTRY 2
3. Spontaneous Processes • Main objective • Spontaneous Reaction- a reaction does occur under specific conditions • Non-spontaneous Reaction- a reaction does not occur under specific conditions • Main objective of thermodynamics is to be able to determine if a reaction will occur when reactants are brought together under certain conditions 4 April 2025 PH 101: PHYSICAL CHEMISTRY 3
4. Spontaneous Processes • A waterfall runs downhill • A lump of sugar dissolves in a cup of coffee • At 1 atm, water freezes below 0ºC and ice melts above 0ºC • Heat flows from a hotter object to a colder object • Iron exposed to oxygen and water forms rust 4 April 2025 PH 101: PHYSICAL CHEMISTRY 4
5. Spontaneous Processes 4 April 2025 PH 101: PHYSICAL CHEMISTRY 5
6. Spontaneous Processes • Which is spontaneous? Be logical. • When it comes down to reactions that cant be seen with the naked eye, we have to look at the properties of the reactions. • Enthalpy, which is a measure of the heat in the system may be able to help determine the spontaneity of a reaction. 4 April 2025 PH 101: PHYSICAL CHEMISTRY 6
7. Spontaneous Processes Does a decrease in enthalpy mean a reaction proceeds spontaneously? Spontaneous reactions 0 CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) H = -890.4 kJ + - 0 H (aq) + OH (aq) H2O (l) H = -56.2 kJ 0 H2O (s) H2O (l) H = 6.01 kJ H O 2 + - 0 NH4NO3 (s) NH4 (aq) + NO3 (aq) H = 25 kJ 4 April 2025 PH 101: PHYSICAL CHEMISTRY 7
8. . • The first two reactions have low enthalpy values and the second two have slighlty positive values. Cannot rely on enthalpy because it does not guarantee a correct prediction of spontaneity. • It allows us to recognize that most exothermic reactions are spontaneous, and that most endothermic reactions are nonsponstaneous. • It is not a guarantee. • We have to look at another thermodynamic quantity to make an accurate prediction. • This is entropy. 4 April 2025 PH 101: PHYSICAL CHEMISTRY 8
9. Entropy • To predict spontaneity we need: – Change in enthalpy – Entropy – Entropy- a measure of the randomness or disorder of a system. – ↑ Disorder = ↑ Entropy 4 April 2025 PH 101: PHYSICAL CHEMISTRY 9
10. Entropy • New Deck Order • Shuffled Deck Order • Probability • Ordered state • Disordered State 4 April 2025 PH 101: PHYSICAL CHEMISTRY 10