What is the difference between exothermic and endothermic reactions?
Difference Between Exothermic and Endothermic Reactions is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. This concept is fundamental for all learners—from Class 10 up to JEE, NEET, and Olympiad aspirants—as it underpins thermodynamics, energy changes, and real-world chemical processes.
What is Difference Between Exothermic and Endothermic Reactions in Chemistry?
A difference between exothermic and endothermic reactions refers to how energy is transferred during a chemical reaction. In an exothermic reaction, energy (usually as heat) is released to the surroundings, making the environment warmer. In contrast, an endothermic reaction absorbs energy from the surroundings, causing a drop in temperature. This concept appears in chapters related to thermodynamics, chemical energetics, and heat flow, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
While exothermic and endothermic reactions are not compounds with a formula, they involve reactants and products interacting based on their bond energies. Both types of reactions involve the breaking of old bonds and the formation of new ones—where energy absorbed or released determines if the reaction is endothermic or exothermic. The overall energy balance comes from comparing the enthalpy (ΔH) of reactants and products.
Preparation and Synthesis Methods
Exothermic and endothermic reactions can be demonstrated with simple lab experiments. Exothermic reactions include burning magnesium ribbon, neutralization between HCl and NaOH, and the thermite process. Endothermic reactions are observed in adding ammonium nitrate to water or dissolving potassium chloride in water. Industrial processes, like combustion in power plants and photosynthesis in nature, also display these phenomena.
Physical Properties of Difference Between Exothermic and Endothermic Reactions
The main physical property differentiating exothermic and endothermic reactions is temperature change:
- Exothermic reactions: Temperature of the surroundings increases; reaction vessel gets warm.
- Endothermic reactions: Temperature of the surroundings decreases; reaction vessel feels cold.
These changes can be tracked using a thermometer during classroom experiments.
Chemical Properties and Reactions
Exothermic reactions commonly involve combination (e.g. fuel combustion) or neutralization, while endothermic reactions are often decomposition (such as thermal decomposition of calcium carbonate) or dissolution processes. The key property is the sign of enthalpy change (ΔH): exothermic (ΔH < 0), endothermic (ΔH > 0).
Frequent Related Errors
- Confusing exothermic and endothermic reactions based only on whether heat is present, without considering overall energy flow.
- Ignoring the use of enthalpy (ΔH) signs in explanation or equations.
- Misunderstanding bond-breaking (usually endothermic) versus bond-making (usually exothermic).
Uses of Difference Between Exothermic and Endothermic Reactions in Real Life
Exothermic and endothermic reactions are everywhere around us. Exothermic reactions are used in hand warmers, self-heating cans, and combustion for cooking or transport. Endothermic reactions appear in instant cold packs for injuries, photosynthesis (plants absorbing energy), and cooking processes like boiling or melting ice. Understanding these helps explain cooling/heating effects in daily activities.
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with difference between exothermic and endothermic reactions, as these concepts appear in reaction-based MCQs, graphs, and energetics problems. Clear knowledge helps in fast elimination and accurate diagram interpretation in exams. Practice with energy profile diagrams and typical reaction equations is highly recommended.
Relation with Other Chemistry Concepts
The difference between exothermic and endothermic reactions is closely related to topics such as enthalpy change, heat of reaction, and types of chemical reactions. Mastery of these connections builds a strong foundation for advanced physical chemistry and connects reaction energetics to practical and theoretical learning.
Step-by-Step Reaction Example
1. Consider the neutralization reaction between hydrochloric acid and sodium hydroxide:2. Write the balanced equation:
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l) + Heat
3. Observe the temperature increase—exothermic reaction (ΔH < 0).
4. For an endothermic example, dissolve ammonium nitrate in water:
5. Balanced Equation:
NH₄NO₃(s) + Heat → NH₄⁺(aq) + NO₃⁻(aq)
6. Temperature falls—endothermic reaction (ΔH > 0).
Lab or Experimental Tips
To remember difference between exothermic and endothermic reactions, always observe the temperature change in the beaker. Vedantu educators recommend holding the test tube after the reaction to “feel” if it's hot (exothermic) or cold (endothermic). Always record initial and final temperatures to support your answer.
Try This Yourself
- List two real-life examples each of exothermic and endothermic reactions.
- Draw and label energy profile diagrams for both reaction types.
- Write the sign of ΔH for an exothermic versus endothermic process.
- Identify from an experiment if a reaction is exothermic or endothermic by observing temperature change.
Final Wrap-Up
We explored difference between exothermic and endothermic reactions—explaining their definitions, features, diagrams, and importance in real life and competitive exams. For more in-depth explanations, solved questions, and revision notes, be sure to check live sessions and study materials on Vedantu.
| Type of Reaction | Heat Flow | Sign of ΔH | Temperature Change | Example |
|---|---|---|---|---|
| Exothermic | Heat is released to surroundings | Negative (< 0) | Increases | Combustion of fuels |
| Endothermic | Heat is absorbed from surroundings | Positive (> 0) | Decreases | Photosynthesis, Melting ice |
Keep revising concepts like enthalpy, chemical reactions, and combustion reaction to strengthen your grasp on difference between exothermic and endothermic reactions.
FAQs on Difference Between Exothermic and Endothermic Reactions Explained
1. What is the difference between exothermic and endothermic reactions?
Exothermic reactions release energy to their surroundings, usually as heat, causing a temperature increase. Endothermic reactions absorb energy from their surroundings, also usually as heat, resulting in a temperature decrease. The key difference lies in the direction of energy flow.
2. Give two examples each of exothermic and endothermic reactions with equations.
Exothermic:
- Combustion of methane: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + heat
- Neutralization of an acid and base: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) + heat
- Photosynthesis: 6CO2(g) + 6H2O(l) + light energy → C6H12O6(aq) + 6O2(g)
- Decomposition of calcium carbonate: CaCO3(s) + heat → CaO(s) + CO2(g)
3. How does temperature change in exothermic vs. endothermic reactions?
In exothermic reactions, the temperature of the surroundings increases because heat is released. In endothermic reactions, the temperature of the surroundings decreases because heat is absorbed.
4. How to identify a reaction as exothermic or endothermic using graphs?
In an exothermic reaction graph, the products have lower energy than the reactants. The difference represents the heat released. In an endothermic reaction graph, the products have higher energy than the reactants; the difference shows the heat absorbed. Look for the relative positions of the reactants and products on the energy axis.
5. What happens to ΔH in these reactions?
ΔH (change in enthalpy) is negative for exothermic reactions (energy is released), and positive for endothermic reactions (energy is absorbed).
6. What is an example of an endothermic reaction in everyday life?
Melting ice is a common example of an endothermic process. The ice absorbs heat from its surroundings to change from a solid to a liquid state.
7. What is an example of an exothermic reaction in everyday life?
Burning wood in a campfire is a classic example of an exothermic reaction. The combustion process releases heat and light into the surroundings.
8. What is the significance of activation energy in exothermic and endothermic reactions?
Activation energy is the minimum energy required to initiate a chemical reaction. Both exothermic and endothermic reactions need this initial energy input, even though exothermic reactions overall release more energy than they consume.
9. How do bond breaking and bond formation relate to reaction energetics?
Breaking chemical bonds requires energy (endothermic), while forming new bonds releases energy (exothermic). Whether a reaction is overall exothermic or endothermic depends on the net energy change: the difference between the energy required to break bonds and the energy released when forming new bonds.
10. What is Gibbs Free Energy and its relevance to exothermic and endothermic reactions?
Gibbs Free Energy (ΔG) predicts the spontaneity of a reaction. It considers both enthalpy (ΔH) and entropy (ΔS). A negative ΔG indicates a spontaneous reaction, which can be exothermic or endothermic, depending on the interplay between ΔH and ΔS.
11. Can a reaction be both exothermic and endothermic?
A single reaction cannot be simultaneously exothermic and endothermic under the same conditions. However, a reaction might exhibit different characteristics at different stages or under varying conditions. For example, the overall reaction may be exothermic but some intermediate steps might be endothermic.
12. How is heat of reaction measured?
The heat of reaction, or enthalpy change, is measured using a calorimeter. This device measures the heat absorbed or released during a chemical reaction, allowing for the calculation of ΔH.
