To figure out a reaction type (if it is Exothermic Vs Endothermic), what can help?
How to decide system vs environment ?

for example,
A metal pipe is cooling-----> Here the system is metal pipe and the environment is atmosphere. System is releasing(losing heat) and it is exothermic.

If we pour H2SO4 in water (like dilution of H2SO4) water temperature increases.-->
Here system is H2SO4 and environment is the water around H2SO4?
Or
H2SO4 with water forms the system
and the environment is the atmosphere?

In this scenario, water temperature increase and that's why it is exothermic OR heat is released to the atmosphere and that's why it is exothermic...What is the right way of understanding?

Appreciate your reply..

The heat release by a chemical reaction is called exothermic. The opposit is endothermic. So it's the dilution of sulfuric acid. H2SO4 + H2O => H3O+ + HSO4- + heat. which produce the most heat.
The exchange with the environment like cooling down a hot pipe  is not called like this.

Quote from: prasamb@yahoo.com on November 05, 2022, 09:59:03 AM
To figure out a reaction type (if it is Exothermic Vs Endothermic), what can help?
How to decide system vs environment ?

for example,
A metal pipe is cooling-----> Here the system is metal pipe and the environment is atmosphere. System is releasing(losing heat) and it is exothermic.

If we pour H2SO4 in water (like dilution of H2SO4) water temperature increases.-->
Here system is H2SO4 and environment is the water around H2SO4?
Or
H2SO4 with water forms the system
and the environment is the atmosphere?

In this scenario, water temperature increase and that's why it is exothermic OR heat is released to the atmosphere and that's why it is exothermic...What is the right way of understanding?

Appreciate your reply..

System is the part in observation and everything around the system is the surroundings.
In case of your metal pipe --immediate surroundings is atmosphere and if you put this pipe in water than water is the surroundings.
In case of H₂SO₄ dilution ?H₂SO₄ is the system and its dissociation in water is the reaction and part of the system However all remaining water which is in excess is the surroundings.
In cup calorimeter ?.water is the surroundings and you are measuring rise or fall of temperature of water.
If reaction is exothermic then water temperature will rise and process is endothermic for water.
If reaction is endothermic then it will take heat from water and there is fall in temperature  of water.
q _system = - q _water
This is the equation we use in cup calorimeter questions.
delta H (reaction) = - q _water / n