Entropy and FREE ENERGY! Spontaneous or NOT!

The change in energy in a reaction is the first factor that allows scientists to predict whether a reaction is spontaneous or not. The randomness of the particles in a system is the second factor in determining the spontanaeity of a reaction.

Most spontaneous reactions are exothermic because they don’t require an input of energy But some endothermic reactions can be spontaneous for example ice melting (energy is absorbed from the atmosphere). This indicates that there is another factor other than enthalpy that drives the reaction.

In nature reactions progress from higher energy to lower energy to become more stable. In general this means from a more orderly state to a more disorganized state.

ENTROPY This is the degree of randomness in a system. For example solid particles are more orderly than liquid particles…….liquid particles are more random and therefore have more entropy. ΔS = change in entropy Increase in entropy = +ΔS Decrease in entropy = -ΔS

FREE ENERGY Nature causes reactions to proceed towards least enthalpy and more entropy. A combined enthalpy and entropy function is called the free energy (G) of a system. Natural processes tend to lower the free energy in a system.

Free-energy change ΔG = ΔH - T ΔS

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