Exothermic Reaction MCQs Quiz | Class 10
This Class X Science (Code 086) quiz covers Unit I: Chemical Substances – Nature and Behaviour. The topic focuses on Exothermic Reactions, including heat released, specific examples like respiration and combustion, and identification methods. Test your knowledge, submit your answers, and download the solution PDF for revision.
Understanding Exothermic Reactions
An exothermic reaction is a chemical reaction that releases energy by light or heat. It is the opposite of an endothermic reaction. In thermodynamics, the term describes a process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in the form of light (e.g., a spark, flame, or flash), electricity (e.g., a battery), or sound (e.g., explosion heard when hydrogen burns).
Key Characteristics
- Temperature Rise: The most common sign of an exothermic reaction is an increase in the temperature of the reaction mixture and container.
- Energy Release: Energy is released because the total energy of the products is less than the total energy of the reactants.
- Enthalpy Change: The change in enthalpy (Delta H) is negative for exothermic reactions.
Common Examples in Class 10 Syllabus
It is crucial to remember specific examples often asked in exams:
- Respiration: Glucose combines with oxygen in the cells of our body and provides energy. This is an exothermic process.
- Burning of Natural Gas: Methane burns in oxygen to produce carbon dioxide, water, and heat.
- Decomposition of Vegetable Matter: The breakdown of vegetable matter into compost is also an example of an exothermic reaction.
- Reaction of Quicklime with Water: When Calcium Oxide reacts vigorously with water to produce Calcium Hydroxide (slaked lime), a large amount of heat is released.
Comparison: Exothermic vs. Endothermic
| Feature | Exothermic | Endothermic |
|---|---|---|
| Heat Flow | Releases heat to surroundings | Absorbs heat from surroundings |
| Temperature | Temperature increases | Temperature decreases |
| Delta H Sign | Negative | Positive |
Quick Practice Questions
- 1. Is photosynthesis exothermic or endothermic? (Answer: Endothermic)
- 2. What gas is evolved when zinc reacts with dilute sulfuric acid? (Answer: Hydrogen)
- 3. True or False: Bond breaking releases energy. (Answer: False, bond breaking requires energy; bond formation releases energy.)
- 4. What happens to the test tube when quicklime is added to water? (Answer: It becomes hot.)
- 5. Is the burning of a candle exothermic? (Answer: Yes)
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