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प्रश्न
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 water to quicklime.
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उत्तर
Addition of water to quick lime: Hissing sound accompanied by a lot of heat (boiling).
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संबंधित प्रश्न
Changes in which new substances are formed are called ______ changes.
Complete and balance the following chemical equations:
Ba`"CI"_2` + `"H"_2"SO"_4` `→`
(aq.) (aq.)
FILL IN THE BLANK
A .............. change is a temporary change.
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........... electrolytes dissociate completely in aqueous state and allow large amount of electricity to flow through it.
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Positively charged ions are called ........
Give an example of a reaction where the following are involved
Heat
Write the chemical reaction where the following changes are observed.
Colour change is noticed
Write the chemical reaction where the following changes are observed.
Precipitate is formed
Multiple choice:
Which of the following is not a characteristic of a chemical change?
State the main characteristics of chemical reactions. Give at least one example in each case.
Give a chemical test to distinguish between the following gases.
H2 and O2
Distinguish by heating the following in dry test tubs.
Ammonium Chloride and iodine.
Match the chemical reactions in List I with the appropriate answer in List II.
| List I | List II | ||
| 1. | \[\ce{XY⇌[heat]X + Y}\] | A: | Displacement reaction |
| 2. | \[\ce{XY->X + Y}\] | B: | Double decomposition |
| 3. | \[\ce{X+Y- + A+B^-->X+B- + A+Y-}\] | C: | Endothermic reaction |
| 4. | \[\ce{X + YZ->XZ + Y}\] | D: | Thermal dissociation |
| 5. | \[\ce{X + Y->[heat]XY -\Delta}\] | E: | Decomposition reaction |
State whether the following reaction is oxidation or reduction.
\[\ce{Na->Na+}\]
________ is a chemical substance which alters the speed of a chemical reaction.
Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.
Which of the following is/are true when milk changes into curd?
- Its state is changed from liquid to semi solid.
- It changes colour.
- It changes taste.
- The change cannot be reversed.
Choose the correct option from below:
Chemical changes are important in our day-to-day life. Give examples.
Why is spoiling food a chemical change?
Both CO2 and H2 gases are ______.
