AP Chemistry Unit Review
Unit 6: Thermodynamics
How it applies to our lives
Have you ever used a hot or cold pack in your life? Have you wondered how heat is transferred from these things? When you pop an instant cold pack, it starts an endothermic reaction that absorbs heat and makes your injured ankle feel cold. On the other hand, activating a chemical hand warmer starts an exothermic reaction that releases heat, making your freezing hands feel hot.
Key Vocabulary
Select a card to reveal its definition.
Energy
Kinetic energy (KE)
Potential energy (PE)
First Law of Thermodynamics
Second Law of Thermodynamics
Heat (q)
Main Takeaways
The First Law of Thermodynamics and Internal Energy: Energy cannot be created nor destroyed, only transferred between a system and its surroundings as heat (q) and work (w).
Enthalpy and Heat Flow: Enthalpy change (delta H) measures the heat gained or lost by a system at constant pressure. Exothermic reactions release heat (negative delta H), while endothermic reactions absorb heat (positive delta H).
Hess’s Law and State Functions: Enthalpy is a state function; the total enthalpy change for a reaction is the same whether it happens in one single step or multiple steps.
Calorimetry Measures Heat Transfer: This experimental technique uses a substance’s heat capacity to calculate how much energy is required to change its temperature during a chemical or physical change.
Standard Enthalpies of Formation: Total enthalpy change is calculated by subtracting the total enthalpy of formation of the reactants from that of the products (Products - Reactants).
Common Misconceptions
Many believe breaking chemical bonds releases energy. In reality, breaking a bond ALWAYS requires energy (endothermic), and energy is only released when NEW bonds are formed (exothermic).
Unit Quiz
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