# Entropy Key Points and Definitions

## 1. The standard entropy change of a reaction can be calculated using the standard entropies of the reactants and products:

• ΔSºreaction = ΣSº(products) - ΣSº(reactants)
• The entropy content of one mole of the substance under standard conditions
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## 2. If a change makes a system more random ΔH is positive, and if a change makes a system more ordered, ΔS is

• Negative
• ΔSºreaction = ΣSº(products) - ΣSº(reactants)

## 3. The standard entropy S, of a substance is

• The entropy content of one mole of the substance under standard conditions
• S is always a positive number

## 4. In a reaction where there is an increase in the number of gaseous molecules, entropy

• Increases
• ΔSºreaction = ΣSº(products) - ΣSº(reactants)
• Decreases

## 5. For an endothermic reaction to take place spontaneously, ΔS must be positive, and the temperature must be high enough so that

• TΔS>ΔH
• TΔS
• The balance between enthalpy, entropy, and temperature for a process: ΔG = ΔH - TΔS