Thermodynamics Entropy, Free Energy, and the Direction of Chemical Reactions

Thermodynamics Entropy, Free Energy, and the Direction of Chemical Reactions 

Down s Easier than Up After an initial push, a sled goes down a hill by itself, but you must continually pull it up. In the same sense, as you ll learn in this chapter, some reactions occur by themselves once started, while others occur only through a continual input of energy. 

A process, such as a rock falling or a fuel burning, is called spontaneous because, once started, it continues by itself. A nonspontaneous process requires a continuous input of energy to occur. A reaction proceeding toward equilibrium is a spontaneous process. 

The total kinetic energy of a system is the sum of the translational, rotational, and vibrational energies of its particles, each of which is quantized. A microstate of fhe system is any specific combination of the quantized energy states of all the particles. The entropy of a system is directly related to the number of microstates over which the system disperses its energy, which is closely associated with the freedom of motion of the particles. A substance has more entropy in its gaseous state than in its liquid state, and more in its liquid state than in its solid state. 

We predict the direction of a spontaneous change from the second iaw of thermodynamics a spontaneous change occurs in the direction that increases the entropy of the universe (system plus surroundings). In other words, a change occurs spontaneously if the energy of the universe becomes more dispersed. 

The free energy of a system decreases in a spontaneous process that is, if ASi k, 0. AGsys 0. In a coupling of reactions, a spontaneous step with a larger negative AG drives a nonspontaneous step with a smaler positive AG. 

1 The Second Law of Thermodynamics Predicting Spontaneous Change Lrnitations of the First Law The Sign of AH and Spontaneous Change Freedom of Motion and Dispersal of Energy Entropy and the Number of Microstates Entropy and the Second Law Standard Molar Entropies and the Third Law 

The Standard Entropy of Reaction Entropy Changes ri the Surroundings Entropy Change and the Equiibrium State Spontaneous Exothermic and Endothermic Reactions 

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