International Baccalaureate IB Chemistry

Entropy, $S$, is a measure of the dispersal or distribution of matter and/or energy in a system. The more ways the energy can be distributed, the higher the entropy. Under the same conditions, the entropy of a gas is greater than that of a liquid, which in turn is greater than that of a solid.

Predict whether a physical or chemical change will result in an increase or decrease in entropy of a system. 

Calculate standard entropy changes, $\Delta S^\circ$, from standard entropy values.

Change in Gibbs energy, $\Delta G$, relates the energy that can be obtained from a chemical reaction to the change in enthalpy, $\Delta H$, change in entropy, $\Delta S$, and absolute temperature, $T$.

Apply the equation $\Delta G^{\circ} = \Delta H^{\circ} - T\Delta S^{\circ}$ to calculate unknown values of these terms.

At constant pressure, a change is spontaneous if the change in Gibbs energy, $\Delta G$, is negative.

Interpret the sign of $\Delta G$ calculated from thermodynamic data. 

Determine the temperature at which a reaction becomes spontaneous.