Question

what are the observations which help you to determine whether a chemical reaction has taken place give an example of chemical reaction for each observation​

Answer 1

if there is irreversible change takes place then there is chemical reaction occur.for ecample rusting of iron.

Answer 2

The observation are as follows :-

1. There is a change in Temperature.
2. Change in colour.
3. change in state.
4. Evolution of Gas.

for Example :-

1. CaO + H2O ---> Ca(OH)²

here it is a change in temperature .

here the temperature rise up.

2. Ca(OH)²(aq) + CO2(g) ----> CaCO3(s) + H2O(l)

it is a example of change in state.

3. Zn + H2SO4 -----> ZnSO4 + H2

it is a example of evolution of Gas.

HERe hydrogen gas is evolved.

What is Endothermic reaction ?

the Reaction in which heat is absorbed is called endothermic reaction.

for example :-

CaCO3 + Δ -------> CaO + CO2

it is a example of endothermic reaction.

What is Exothermic reaction?

The reaction in which heat is evolved is known as exothermic reaction.

for example :-

CaO + H2O ----> Ca(OH)² + Δ

beacuse here the heat is evolved.

here is your answer....