Entropy and Free Energy

1. Entropy and Free Energy 19.4

2. After reading Section 19.4, you should know: • How to calculate the amount of free energy of a reaction • How to use the free energy to determine whether a reaction will be spontaneous or not

3. Entropy – a quantitative measure of the disorder of a system • Symbol = ΔS0 (Joule / Kelvin* mol) • ΔS0= ΔS0 (products) -ΔS0 (reactants) • Table 19.2 on page 558

4. Practice • Using Table 19.2, determine the standard entropy change(ΔS0 ) for the following reaction. 2NO(g) + O2(g) 2NO2(g) • ΔS0 = ΔS0 (products) -ΔS0 (reactants) ΔS0 = -145.2 J/K • *** Remember to multiply the ΔS0by 2 since • you have 2 mol of NO and NO2

5. Gibbs Free Energy – the energy available to do work • Symbol = ΔG0 (kJ / mol) • ΔG0 = ΔG0 (products) -ΔG0 (reactants) • Table 19.4 on page 563

6. Gibbs Free Energy • If the ΔH (enthalpy) and the ΔS (entropy) are known, the (free energy) can be found by: • ΔG0 = ΔH -T ΔS0 • T = temp in Kelvin • Must convert units!!! • ΔG0 (kJ / mol) • ΔH0 (kJ / mol) • Δ S0 (Joule / Kelvin*mol)

7. Spontaneous or not?? • Spontaneous reactions release free energy • ΔG0 is negative • The system loses free energy • ΔH0 = negative • Δ S0 = positive

8. Spontaneous or not?? • Nonspontaneous reactions absorb free energy • ΔG0 is positive • The system needs the free energy to make the reaction happen • ΔH0 = positive • Δ S0 = negative ** A system may be spontaneous under one set of conditions and nonspontaneous under another (example – if the temperature changes)

9. Values in the book • Free Energy (ΔG0) values – pg 563 • Enthalpy (ΔH0)values – pg 316 • Entropy (Δ S0)values – pg 558

10. After reading Section 19.4, you should know: • How to calculate the amount of free energy of a reaction • How to use the free energy to determine whether a reaction will be spontaneous or not