Question

Define a chemical reaction state 4 observations which help us to determine that a chemical reaction has taken place. write one example of each observation with a balanced chemical equation?

Answer 1

a process in which two or more substances reacts to form some other new substances with new set of properties is called Chemical reaction.

1)change in colour

Zn+CuSO4------ZnSo4+Cu
the colour of cuso4 changes from blue to pale green

2)change in temperature

Zn + H2SO4------ZnSO4 +H2
heat is evolved

Answer 2

Chemical reaction is a process in which one or more reactants are converted into products. The product may be one or more. The chemical reaction can involve an element or a compound which leads to the formation of product or products.

The observation which may be used to show that a chemical reaction has taken place may include;

1. Change in colour- Reaction of Bromine and ethene

( Br2(l) +  C2H4⇒ CHBrCHBr)

2. formation of a precipitate- silver nitrate and NaCl

(AgNO3 (aq) + NaCl= AgCl(s) + NaNO3)

3. Temperature change

4. Change of smell