Mada za sehemu hiiChemical Kinetics, Equilibrium And EnergeticsMada 4
- The rate of chemical reactions
- Factors affecting the rate of chemical reactions
- Reversible and irreversible reactions
- Endothermic and exothermic reactions
Exothermic and endothermic reactions
Exothermic and endothermic reactions are types of reactions that involve changes in the internal energy of reactants and products, which then affect the surrounding environment in terms of heat release or absorption.
Internal energy
Internal energy is the energy stored within the molecules of chemical substances. During a chemical reaction, the internal energy can either decrease (exothermic) or increase (endothermic) depending on whether the reaction releases or absorbs heat. This energy change is reflected by the surrounding temperature, which becomes either hotter or colder after the reaction stops.
Exothermic reactions
An exothermic reaction is one in which heat is released into the surrounding environment, causing the surroundings to get hotter. The internal energy of the reactants decreases as energy is released during the reaction.
Example of exothermic reactions:
- H2(g) + ½O2(g) → H2O(l); ΔH = -286 kJ/mol
- C(s) + O2(g) → CO2(g); ΔH = -406 kJ/mol
In these reactions, the negative sign (ΔH = -) indicates that heat is released, resulting in a decrease in internal energy.
Endothermic reactions
An endothermic reaction is one in which heat is absorbed from the surrounding environment, causing the surroundings to become cooler. The internal energy of the reactants increases as heat is taken in during the reaction.
Example of endothermic reactions:
- ½N2(g) + ½O2(g) → NO(g); ΔH = +90.3 kJ/mol
- C(s) + 2S(s) → CS2(l); ΔH = +117 kJ/mol
In these reactions, the positive sign (ΔH = +) indicates that heat is absorbed, resulting in an increase in internal energy.
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