Enthalpy and Entropy
Thermodynamics describes how energy is transferred in chemical reactions, with enthalpy measuring heat exchange and entropy measuring the degree of disorder in a system.
What You Need to Know
Key Concept Diagram
Enthalpy (H) is the heat content of a system; change in enthalpy (delta H) is the heat released or absorbed
Exothermic reactions release heat to the surroundings (delta H < 0)
Endothermic reactions absorb heat from the surroundings (delta H > 0)
Entropy (S) measures the degree of disorder or randomness in a system
Reactions are spontaneous when the decrease in Gibbs free energy (G = H - TS) is negative
Key Vocabulary
Enthalpy
A measure of the total heat content of a system at constant pressure
Exothermic reaction
A reaction that releases heat energy to the surroundings; delta H is negative
Endothermic reaction
A reaction that absorbs heat energy from the surroundings; delta H is positive
Entropy
A measure of the disorder or randomness of a system
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
In an exothermic reaction:
Question 2
Which process involves an increase in entropy?
Question 3
If delta H is negative and delta S is positive, the reaction is:
Key Concepts Summary
- ●Enthalpy (H) is the heat content of a system; change in enthalpy (delta H) is the heat released or absorbed
- ●Exothermic reactions release heat to the surroundings (delta H < 0)
- ●Endothermic reactions absorb heat from the surroundings (delta H > 0)
- ●Entropy (S) measures the degree of disorder or randomness in a system
- ●Reactions are spontaneous when the decrease in Gibbs free energy (G = H - TS) is negative