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प्रश्न
Give examples of exothermic reactions i.e. heat evolved in each of the following:
(a) reaction between a solid and a liquid
(b) reaction between two gases
Give two examples of exothermic reactions seen in everyday life.
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उत्तर
(a) Reaction between a solid and a liquid:
CaO + H2O → Ca(OH)3 + Δ
(b) Reaction between two gases are:
\[\ce{N2 + 3H2 ⇌[Fe-450°][200 atoms.] 2NH3 + \triangle}\]
[finely divided iron (Fe) - catalyst]
Examples of exothermic reactions are:
- Rusting of iron – the reaction is slow and the heat evolved is very less, hence unnoticeable.
- Setting of cement – cement setting liberates heat, hence concrete structures are set slowly.
- Human Body – many chemical reactions in our body are exothermic & provide energy to survive.
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संबंधित प्रश्न
Give one example that illustrates the following characteristics of a chemical reaction:
Change in state
MULTIPLE CHOICE QUESTIONS
Tick the most appropriate answer.
Reduction is a chemical reaction in which there is
- removal of hydrogen
- removal of oxygen
- addition of oxygen
- none of these
FILL IN THE BLANK
In a ............ change, new substances are formed.
Name three reducing agents ?
Fill in the blank
A new substance is always formed in a _______ change.
Fill in the blank:
The substances which undergo chemical change are called _______
What is the reaction called when oxidation and reduction take place simultaneously? Explain with one example.
Out of sodium and sulphur which is a metal? Explain its reaction with the oxygen.
Explain by writing a word equation.
Hard water gets softened on mixing with a solution of washing soda.
Show with the help of diagram of electronic configuration how the following compound is formed from the constituent atoms.
Hydrogen chloride
State the conditions necessary for a chemical change or reaction.
State the original colour of the following substance and colour of residue obtained after heating.
Lead nitrate
A chemical reaction is often accompanied by external indications or characteristics.
Give two examples where a chemical reaction is accompanied by a change in colour of the reactants and products on completion of the reaction.
Complete the statement by filling in the blank with the correct word:
The reddish-brown precipitate obtained during a double decomposition precipitation reaction between an iron salt and alkali is __________.
Explain the following statement: Digestion is a chemical change.
The water we drink is a combination of hydrogen and oxygen.
Write some materials prepared by chemical changes.
When magnesium is burnt in the air, a new substance is formed which is ______.
Both CO2 and H2 gases are ______.
