Endothermic and Exothermic Reaction

Endothermic and Exothermic reaction

You will find those words if you have studied about chemistry. The endothermic and exothermic reaction is very important if we talk about the delta of temperature of a reaction.

These are the simplest definition about endothermic and exothermic reaction.

·         Endothermic reaction.

Endo mean inner, thermic mean temperature, and reaction mean reaction. So, we can conclude that endothermic reaction is a chemical reaction that absorb heat from surrounding that make the temperature of the reaction raises. So, if we measure the surrounding temperature, the surrounding temperature will decrease. See the illustration.

Illustration of endothermal reaction

Because absorb the heat from surrounding so the deltaH of reaction is always + (positive)

Example

CaCO3(s) →  CaO(s) + CO2(g) ; DH = +178.5 kJ (with deltaH)

CaCO3(s) →  CaO(s) + CO2(g) – 178.5 kJ (without deltaH)

The other example of endothermic reaction is

KNO3(s) + H2O(l) → KNO3(aq)

·         Exothermic reaction.

Same with endothermic reaction, Exo mean outer, thermic mean temperature, and reaction mean reaction. So, we can conclude that exothermic reaction is a chemical reaction that release heat to surrounding that make the temperature of the reaction falls. So, if we measure the surrounding temperature, it will raises. See the ilustration.

Illustration of exothermal reaction

Because release the heat to surrounding so the deltaH of reaction is always - (negative)

Example

 C(s) + O2(g)  →  CO2(g) ; DH = -393.5 kJ (with deltaH)

 C(s) + O2(g)  →  CO2(g) + 393.5 kJ (without deltaH)

The other example of endothermic reaction is

C3H8(g) + 3O2(g) → 3CO2(g) + 4H2O(l)

2Mg(s) + O2(g) → 2MgO(s)

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

H2SO4(aq) + 2KOH(aq) → K2SO4(aq) + 2H2O(l)

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