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Energy Changes & Reaction Rates - Coggle Diagram
Energy Changes & Reaction Rates
Energy Changes
Endothermic
absorbs heat
Energy is absorbed because product bonds are weaker than reactant bonds.
ΔH > 0
Temperature of surroundings decreases.
Enthalpy (ΔH)
endothermic / − exothermic
Represents the overall heat change of a chemical reaction under constant pressure.
ΔH = H(products) − H(reactants)
+ΔH → Endothermic (absorbs heat)
−ΔH → Exothermic (releases heat)
kJ/mol
Exothermic
releases heat
combustion of alkanes
Release heat energy to surroundings
Energy is released because product bonds are stronger than reactant bonds.
ΔH < 0 (negative enthalpy change).
Temperature of surroundings increases.
Reaction Rate Factors
Concentration ↑
more collisions
Temperature ↑
faster molecular motion
Surface Area ↑
faster reactions
Catalysts
lower activation energy
(e.g., Ni in hydrogenation)
Pressure ↑
faster gas reactions
Energy Diagram
Endothermic
products higher than reactants
Label
Activation Energy
ΔH
Reactants
Products
Exothermic
products lower than reactants
Real-life Applications
Combustion
cars
alkanes burn exothermically
Industrial synthesis
polyethylene from ethene
Biological systems
ATP reactions
Environmental impact
CO₂ emissions
green chemistry
Incomplete combustion → CO (toxic
Organic Chemistry Example
Alkanes
exothermic combustion
Catalytic hydrogenation
uses catalyst to lower Eₐ
Alkenes/Alkynes
undergo addition reactions
nthalpy changes explain reactivity trends
Addition reaction → exothermic
Hydrogenation (Ni catalyst, ΔH < 0)
C₂H₄ + H₂ → C₂H₆