Understanding Exothermic and Endothermic Reactions
Analogy- Consider you’re holding two beakers.
- In one, you mix hydrochloric acid with magnesium, and almost immediately, the beaker becomes warm to the touch.
- In the other, you dissolve ammonium nitrate in water, and the beaker feels cold.
- Why do these reactions behave so differently?
- The answer lies in how energy is transferred between the reaction system and its surroundings, defining the concepts of exothermic and endothermic reactions.
Energy Transfer in Reactions: The Basics
- Every chemical reaction involves breaking bonds in reactants and forming bonds in products.
- The overall energy change of a reaction depends on the balance between these two processes.
Breaking bonds requires energy (endothermic), while forming bonds releases energy (exothermic).
The System and the Surroundings
- System: The part of the universe where the reaction occurs (e.g., the reactants and products).
- Surroundings: Everything else, including the container and the air around it.
Energy transfer can occur in two directions:
Definition
Exothermic reactions
Energy is released from the system into the surroundings, increasing the temperature of the surroundings.
Definition
Endothermic reactions
Energy is absorbed by the system from the surroundings, decreasing the temperature of the surroundings.
- This transfer of energy is most commonly observed as heat.
- Let’s explore these two types of reactions in detail.
Exothermic Reactions: Energy Released
- In an exothermic reaction, the energy required to break bonds is less than the energy released when new bonds are formed.
- The excess energy is transferred to the surroundings, often as heat.
