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Question
A chemical reaction is often accompanied by external indications or characteristics which include –
- Colour change
- Effervescence or gas evolved
- Evolution or absorption of heat
- Formation of a precipitate.
With reference to each of the above indications, state the external indication seen during – Addition of dilute acid to an active metal.
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Solution
Addition of dil. acid to an active metal: Gas is evolved, test tube or flask becomes hot (heat is produced).
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RELATED QUESTIONS
Changes in which new substances are formed are called ______ changes.
Give one example that illustrates the following characteristics of a chemical reaction:
Change in state
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A .............is a substance which changes the rate of a chemical reaction without undergoing a chemical change.
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........... electrolytes dissociate completely in aqueous state and allow large amount of electricity to flow through it.
MATCH THE COLUMNS
| 1 . `H_2` + `CI_2` `→` 2HCI | a. displacement reaction |
| 2. `2FeCI_3`+ `H_2` `→` `2FeCI_2` +2HCI` | b. addition of an electronegative redical |
| 3. Fe + `CuSO_4` `→``FeSO_4` +Cu` | c. removal of an electronegative redical |
| 4. `2H_2O` +`4NO_2`+`O_2` `→` `4HNO_3` | d.reduction by adding hydrogen |
| 5. 3Fe +`3CI_2` `→` `2FeCI_3` | e.electrolysis of water |
| 6. `FeCI_3`+ 3NaOH `→``Fe(OH)_3``↓`+NaCI | F.double decomposition,precipitation reaction |
| 7.`2H_2O` `→` `2H_2``↑`+`O_2` | e. combination or synthesis reaction |
TRUE \ FALSE
A precipitation reaction takes place only in a solution.
Write true or false :
When iron and sulphur are heated together a grey mass is formed which is attracted by a magnet .
Choose the correct option from the bracket and explain the statement giving reason.
(Oxidation, displacement, electrolysis, reduction, zinc, copper, double displacement, decomposition)
To prevent rusting, a layer of ______ metal is applied on iron sheets.
Complete the statement by filling the gap using an appropriate term from the terms given in the bracket.
(slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign)
An ______ is drawn in between the reactants and products while writing the equation for a chemical reaction.
Define the following term:
Precipitate
Give an example of a reaction where the following are involved
Heat
Multiple choice:
Which of the following is not a characteristic of a chemical change?
Complete and balance the following reaction:
NaCl(aq) + AgNO3(aq) →
Distinguish by heating the following in dry test tubs.
Ammonium Chloride and iodine.
Which of the following is a chemical change?
When magnesium is burnt in the air, a new substance is formed which is ______.
Write the equation for the process of formation of rust.
Assertion (A): Cutting paper into very small pieces is an irreversible change.
Reason (R): Physical changes are always reversible.
The reaction of H2 gas with oxygen gas to form water is an example of ______.
Write the effects of chemical reactions.
