Energy in Reactions
Learn
Exothermic vs. Endothermic
- Exothermic: Releases energy (products have less energy than reactants). Temperature rises.
- Endothermic: Absorbs energy (products have more energy than reactants). Temperature drops.
Activation Energy
The minimum energy needed to start a reaction. Catalysts lower activation energy without being consumed.
Practice Problems
Problem 1: Combustion of methane releases heat. Is this exothermic or endothermic?
Answer: Exothermic (releases energy)
Problem 2: Photosynthesis requires sunlight energy. Classify this reaction.
Answer: Endothermic (absorbs energy)
Problem 3: In an energy diagram, products are lower than reactants. What type of reaction?
Answer: Exothermic (energy was released)
Problem 4: A cold pack feels cold when activated. Is the reaction exothermic or endothermic?
Answer: Endothermic (absorbs heat from surroundings)
Problem 5: Hand warmers release heat. Classify this reaction.
Answer: Exothermic
Problem 6: What does a catalyst do to activation energy?
Answer: Lowers it, making the reaction faster
Problem 7: Melting ice requires energy input. Classify this process.
Answer: Endothermic
Problem 8: Rusting of iron releases small amounts of heat over time. Classify.
Answer: Exothermic (slow oxidation)
Problem 9: Baking soda and vinegar feel cold when mixed. Is this exo- or endothermic?
Answer: Endothermic
Problem 10: The summit of an energy diagram represents what?
Answer: The transition state (highest energy point, activation energy barrier)