AP Chemistry 6.2 Energy Diagrams Study Notes - New Syllabus Effective fall 2024
AP Chemistry 6.2 Energy Diagrams Study Notes.- New syllabus
AP Chemistry 6.2 Energy Diagrams Study Notes – AP Chemistry – per latest AP Chemistry Syllabus.
LEARNING OBJECTIVE
Represent a chemical or physical transformation with an energy diagram.
Key Concepts:
- Energy of Phase Changes
- Exothermic & Endothermic Reactions
- Energy Diagrams
- Thermal Energy & Molecular Collisions
6.2.A.1 Energy Diagram: Endothermic vs. Exothermic Processes:
1. Energy Diagrams:
i. Reaction Coordinate (x-axis): The progress of the reaction from reactants to products.
ii. Energy (y-axis): The system’s energy during the reaction.
iii. Reactants: Starting energy level on the left side.
iv. Products: Ending energy level on the right side.
v. Activation Energy (Ea): Energy required to reach the transition state (the peak).
vi. Transition State: The unstable, high-energy position of the reaction.
Endothermic vs. Exothermic:
– Endothermic Reactions: Products are more energy-rich than reactants (energy is absorbed). The diagram curves upwards, and energy difference is the energy absorbed.
– Exothermic Reactions: Products are less energy-rich than reactants (energy is released). The diagram curves downwards, and the energy difference is the energy released.
Energy diagrams help in the determination of activation energy, reaction rate, and the determination if a reaction is endothermic or exothermic.
2. Endothermic vs. Exothermic Processes:
| Property | Endothermic Processes | Exothermic Processes |
|---|---|---|
| Energy Flow | Absorb energy (heat) from the surroundings | Release energy (heat) to the surroundings |
| Energy of Products | Higher than the reactants | Lower than the reactants |
| Temperature Change | Feels cold to the touch (energy absorbed) | Feels warm or hot to the touch (energy released) |
| Energy Requirement | Require continuous energy input to proceed | Do not require continuous energy input |
| Examples | – Photosynthesis | – Combustion (e.g., burning wood, gasoline) |
| – Melting ice | – Respiration (energy release in cells) | |
| – Boiling water | – Freezing water | |
| – Evaporation of water | – Condensation of steam |
3. Activation Energy and Enthalpy:
i. Activation Energy (Ea):
– Energy needed for the reaction to be started.
– Regulates the rate of the reaction: bigger Ea = slower reaction, smaller Ea = faster reaction.
– The energy hurdle to create the transition state.
ii. Enthalpy (ΔH):
– ΔH = Energy of products – Energy of reactants.
– Endothermic Reactions: ΔH > 0 (energy is absorbed, products higher in energy).
– Exothermic Reactions: ΔH < 0 (energy released, products less energetic).
iii. Summary:
– Activation energy is the energy needed to start a reaction.
– ΔH tells us if a reaction is endothermic (ΔH > 0) or exothermic (ΔH < 0).
4. Real-World Applications:
i. Industrial Chemistry:
– Maximize reaction rates by adjusting temperature and catalysts to lower activation energy.
– Example: Haber Process for the production of ammonia.
ii. Biochemical Reactions:
– Explain how enzymes lower activation energy to speed up metabolic processes.
– Example: Digestion.
iii. Combustion Reactions:
– Forecast energy release and optimize fuel consumption in power plants and engines.
– Example: Gasoline Engines.
iv. Environmental Science:
– Models chemical reactions that affect the environment, i.e., ozone depletion.
– Example: Ozone Layer Depletion.
v. Pharmaceuticals:
– Helps in designing medications by explaining activation energy and pathways of reaction.
– Example: Drug Synthesis.
Endothermic
- Products have more energy than reactants
- +
- Ex: decomposition reaction
- +
- Forward reaction has higher activation energy than reverse
Exothermic:
- Products have less energy than reactants
- –
- Ex: synthesis reactions
- –
- Reverse reaction has higher activation energy that forward reaction
- Energy gained by the surroundings must be equal to the energy lost by the system
