Topic 15.3: Entropy

15.3.1 State and explain the factors that increase the entropy in a system

The degree of disorder of a system is quantified by its entropy (S)

Two factors that affect the disorder of a system:

• State of matter

Solid don't move around as much as a gas particle.

• Number of moles

More particles, more chaos (More people at a party, More chaos and fun)

(After IB)

15.3.2 Predict whether the entropy change for a given reaction or process is positive or negative

• First, you check how many moles of molecules. In this case both sides of the equation are equal.
• Second, check the state of matter. The right hand side has a solid instead of an aqueous. Thus we could conclude that this reaction has a lowering entropy value.

Thus, in this equation, entropy value is decreasing.

15.3.3 Calculate the standard entropy change for a reaction using standard entropy values.

This is the equation for entropy change.

It is important to note that all entropy values are positive. With the entropy values increase in the order of solid < liquid < gas. As entropy depends on the temperature and pressure, tabulated entropy values refer to standard conditions.

Table 11 of the data booklet has a list of values for organic compounds.