Wanna know what is the difference between endothermic and exothermic reactions in tabular form? If yes, then look no further! As per the laws of thermochemistry, a chemical reaction can be divided into two sub-categories. These are endothermic and exothermic reactions.
An endothermic reaction absorbs energy from its surroundings. And, an exothermic reaction releases energy to its surrounding. The energy released or absorbed can be either in the form of heat, cold, light, or, sound.
Endothermic vs Exothermic
| Endothermic Reaction | Exothermic Reaction | |
| 1. | An endothermic reaction absorbs energy from its surroundings. | An exothermic reaction releases energy to its surrounding. |
| 2. | Energy is absorbed in the form of heat. | Energy is released in the form of sound, heat, and light. |
| 3. | The change in enthalpy is positive. | The change in enthalpy is negative. |
| 4. | The enthalpy of products is always greater than the reactants. | The enthalpy of products is always less than the reactants. |
| 5. | Temperature decreases with the progression of endothermic reactions. | Temperature increases with the progression of exothermic reactions. |
| 6. | An endothermic reaction is a type of endergonic reaction. | An exothermic reaction is a type of exergonic reaction. |
| 7. | Examples of endothermic reactions include Evaporation, Instant Cold packs, cooking, etc. | Examples of exothermic reactions include condensation, nuclear reactions, rusting of iron, etc. |
What is an Endothermic Reaction?
By definition, Endothermic reactions are a type of chemical reaction during which a system absorbs energy from its surroundings. One can also say that the endothermic process requires additional energy from its surroundings to proceed further. That is why the temperature of the surroundings decreases.
For example, when drying wet clothes, the water droplets inside the clothes (system) pull the heat from the surroundings. As a result, the enthalpy of the system (wet clothes) increases which in turn decreases the temperature of the surrounding, at least, a little bit.
Why Change in Enthalpy of Endothermic Reactions is always positive?
Just because the energy (heat) is absorbed by the system from its surroundings, the change in enthalpy of endothermic reactions is always positive. Not to mention, as per other definitions, the enthalpy (energy) of products is higher than the reactants. That’s why it always has a positive value. (See the above diagram and equation written below to understand it properly)
A + B => C +D
ΔH = {HC + HD} – {HA + HB}
ΔH = (Hproducts – Hreactants ) = positive value
where,
A and B are Reactants
C and D are Products
ΔH = Change in enthalpy during the reaction
HA and HB = Enthalpy of A and B
HC and HD = Enthalpy of C and D
Examples of Endothermic Reaction
Some examples of Endothermic reactions are:
- Evaporation
- Photosynthesis
- Instant Cold Pack
- Cooking food
- Salt Dissolving in Water
- Sublimation
- Thermal Decomposition
- Pressure Cookers
- Hydrolysis, etc.
What is an Exothermic Reaction?
By definition, Exothermic reactions are a type of chemical reaction during which a system releases energy to its surroundings. One can say that the exothermic process releases additional energy to its surroundings to proceed further. That is why the temperature of the surroundings increases.
For example, in the case of a nuclear fission reaction, when the uranium is bombarded with a neutron. It splits into two smaller nuclei releasing a large amount of energy which in turn increases the temperature of the surroundings.
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Why Change in Enthalpy of Exothermic Reactions is always negative?
Just because the energy (heat) is released by the system to its surroundings, the change in enthalpy of exothermic reactions is always negative. Not to mention, as per the other definition, the enthalpy (energy) of the products is less than the reactants. That’s why it always has a positive value. (See the above diagram and equation written below to understand it properly).
S + T => U +V
ΔH = {HU + HV} – {HS + HT}
ΔH = (Hproducts – Hreactants ) = negative value
where,
S and T are Reactants
U and V are Products
ΔH = Change in enthalpy during the reaction
HS and HT = Enthalpy of S and T
HU and HV = Enthalpy of U and V
Examples of Exothermic Reaction
Some examples of Exothermic reactions are:
- Nuclear Reactions
- Burning of Candle
- Rusting of Iron
- Deposition
- Condensation
- Lightening a Matchstick
- Hot Packs
- Respiration
- Combustion, etc.
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