What are the differences between endothermic and exothermic reactions?

Question

Accepted Answer

Basis of Differentiation
Endotherimic Reaction
Exothermic Reaction

Definition
A chemical reaction that absorbs energy from its surrounding into the reaction 
A chemical reaction that releases energy from the reaction into the surrounding

Form of energy absorbed/released
The energy absorbed is  in the form of heat
The energy released may be in the form of heat, light, electricity, or sound

Energy provision
Energy needs to be provided from the outside environment for the initiation and progression of the reaction
No external energy is required, instead internal energy is released from the system to the outside environment as the chemical reaction starts and progresses

Increase/decrease in temperature
Because energy is provided from the outside, the temperature decreases as the reaction progresses
Because internal energy is released from the system, the temperature increases as the reaction progresses

Enthalpy (the sum of the internal energy of the reaction + the energy required to maintain the volume and pressure of that system in that environment)
The enthalpy of the reaction is higher than the enthalpy of the reactants – this is because energy is absorbed into the system 
The enthalpy of reaction is lower than that of reactants – this is because energy is released from the reaction

Change in enthalpy
Change in enthalpy of the reaction is a positive value
Change in enthalpy of the reaction is a negative value

Touch test 
After the reaction, the beaker or test tube where the reaction has taken place will be colder than before the reaction started – this is because of the absorption of energy from the outside
After the reaction, the beaker or test tube where the reaction has taken place will be warmer than before the reaction started – this is because the reaction releases energy

Examples
Evaporation, Melting Ice, Photosynthesis, Splitting a Gas Molecule, Cooking an Egg
Rusting Iron, Making Ice, Combustion, Explosions, Nuclear Fission and Fusion, Rain Formation

Basis of Differentiation	Endotherimic Reaction	Exothermic Reaction
Definition	A chemical reaction that absorbs energy from its surrounding into the reaction	A chemical reaction that releases energy from the reaction into the surrounding
Form of energy absorbed/released	The energy absorbed is in the form of heat	The energy released may be in the form of heat, light, electricity, or sound
Energy provision	Energy needs to be provided from the outside environment for the initiation and progression of the reaction	No external energy is required, instead internal energy is released from the system to the outside environment as the chemical reaction starts and progresses
Increase/decrease in temperature	Because energy is provided from the outside, the temperature decreases as the reaction progresses	Because internal energy is released from the system, the temperature increases as the reaction progresses
Enthalpy (the sum of the internal energy of the reaction + the energy required to maintain the volume and pressure of that system in that environment)	The enthalpy of the reaction is higher than the enthalpy of the reactants – this is because energy is absorbed into the system	The enthalpy of reaction is lower than that of reactants – this is because energy is released from the reaction
Change in enthalpy	Change in enthalpy of the reaction is a positive value	Change in enthalpy of the reaction is a negative value
Touch test	After the reaction, the beaker or test tube where the reaction has taken place will be colder than before the reaction started – this is because of the absorption of energy from the outside	After the reaction, the beaker or test tube where the reaction has taken place will be warmer than before the reaction started – this is because the reaction releases energy
Examples	Evaporation, Melting Ice, Photosynthesis, Splitting a Gas Molecule, Cooking an Egg	Rusting Iron, Making Ice, Combustion, Explosions, Nuclear Fission and Fusion, Rain Formation

What are the differences between endothermic and exothermic reactions?

Posted May 13, 2022