Understanding how energy works in chemical reactions is an important part of chemistry. In this chapter, you will learn about system and surroundings, which explain how energy moves during a reaction. You will also study enthalpy, a key concept used to measure heat changes.
In addition, this chapter covers aerobic and anaerobic respiration, helping you understand how living organisms release energy with or without oxygen. These topics are very important for exams and also help in understanding real-life processes.
These Class 9 Chemistry Chapter 5 Energetics Notes are designed according to the 2026 new syllabus. The notes are written in simple English so that every student can easily understand and revise the concepts.
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❓ Frequently Asked Questions (FAQs)
Q1: What is energetics in chemistry?
Energetics is the study of energy changes that occur during chemical reactions.
Q2: What is the difference between system and surroundings?
System is the part of the universe being studied, while surroundings include everything around it.
Q3: What is enthalpy?
Enthalpy is the heat energy change during a reaction at constant pressure.
Q4: What is aerobic respiration?
Aerobic respiration is the release of energy using oxygen.
Q5: What is anaerobic respiration?
Anaerobic respiration is the release of energy without oxygen.
MCQs – Chapter 5 Energetics
Q1: Where does the energy come from to break the bonds of H₂ and Cl₂?
(a) By collisions between the molecules
(b) From sunlight
(c) From the surrounding ✅
(d) By collisions of the molecules with
Q2: In chemistry, the part under study is called:
(a) Atom
(b) Molecule
(c) System ✅
(d) Surrounding
Q3: The standard conditions for enthalpy are:
(a) 25°C and 1 atm ✅
(b) 100°C and 760 mm
(c) 0°C and 760 mm
(d) 37°C and 1 atm
Q4: The heat content of a system is called:
(a) Kinetic energy
(b) Enthalpy ✅
(c) Temperature
(d) Work
Q5: What type of reaction absorbs heat from the surroundings?
(a) Exothermic
(b) Combustion
(c) Endothermic ✅
(d) Neutralization
Q6: Anaerobic respiration produces energy by converting glucose into:
(a) Carbon dioxide and water
(b) Carbon dioxide and ethanol ✅
(c) Oxygen and ethanol
(d) Oxygen and carbon dioxide