Endothermic reaction absorbs heat from environment
An exothermic reaction occurs when the temperature of a system increases due to the evolution of heat. This heat is released
into the surroundings, resulting in an overall negative quantity for the heat of reaction (-ΔE ).
An endothermic reaction
occurs when the temperature of an isolated system decreases while the surroundings of a non-isolated system gains heat.
Endothermic reactions result in an overall positive heat of reaction (+ΔE ).
Exothermic and endothermic reactions cause energy level differences and therefore differences in enthalpy (ΔE ), the sum of
all potential and kinetic energies.
ΔH is determined by the system, not the surrounding environment in a reaction.
A system
that releases heat to the surroundings, an exothermic reaction, has a negative ΔH by convention, because the enthalpy of the
products is lower than the enthalpy of the reactants of the system.
The enthalpies of these reactions are less than zero, and are therefore exothermic reactions.
A system of reactants that absorbs
heat from the surroundings in an endothermic reaction has a positive , because the enthalpy of the products is higher than
the enthalpy of the reactants of the system.
Because the enthalpies of these reactions are greater than zero, they are endothermic reactions.
EDIT ( See this )
I understand your confusion. See, in endothermic reaction the product will be &quot;colder&quot;....this might seem counterintuitive as in endothermic reaction heat is absorbed by the system form the environment. Therefore the heat absorbed must increase the temperature right?
No! See temperature shows the direction of heat flow. If the temperature of the system increased ( assuming that previously the system and environment were in thermal equilibrium ~ same temperature ) this would mean that heat should flow from system to the environment as the system has a higher temperature than environment.
The following example makes everything clear:
$$T_{(env)}= 25°$$
$$A + B _{(25°)}  = C _{(20°)}  ...... (1)$$
$$A' + B' _{(25°)}  = C' _{(30°)} ..... (2)$$
Compare the temperature of system and environment in the above rxn.
Therefore in rxn. 1 heat flows from environment to system ( from 25° to ~20°).
This heat energy is used to break bonds and stuff.( Endothermic )
And in rxn. 2 heat flows from system to environment ( from 30° to 25°).( Exothermic )
Also see this practical video:
https://youtu.be/NHOHKH3808c