Chemistry
One of the conditions necessary for a chemical reaction to occur is :
- Evolution of a gas
- Physical contact between reactants
- Change in colour
- Formation of a precipitate
Chemical Reaction
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Answer
Physical contact between reactants
Reason — For a chemical reaction to take place, the reactants must come into close contact, i.e., they should be mixed.
Others are outcomes of a reaction not necessary conditions for a chemical reaction. Gas may or may not be produced in some reactions. Some reactions show colour change. But many reactions occur without any visible colour change. A precipitate is formed only in certain reactions not in all.
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Related Questions
This gas has a rotten egg smell:
- Ammonia
- Hydrogen
- Hydrogen sulphide
- Oxygen
When sodium carbonate reacts with dilute hydrochloric acid, the gas evolved is:
- Carbon dioxide
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What happens when a chemical reaction takes place ?
- A precipitate is formed
- A gas is evolved
- The substance changes its colour
- All of the above
Assertion (A): A chemical reaction can be written in the form of a chemical equation with the help of symbols and formulae of the substances involved.
Reason (R): In a chemical equation, the reactants are written on the right hand side and products are written on the left hand side of the arrow.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.