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प्रश्न
Give reason for the following:
Even though rusting is an exothermic reaction, the heat evolved when an iron nail rusts is unnoticeable.
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उत्तर
Rusting of iron – the reaction is slow and the heat evolved is very less, hence unnoticeable.
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संबंधित प्रश्न
Changes in which new substances are formed are called ______ changes.
Complete and balance the following chemical equations
NaCI + `AgNO_3` `→`
FILL IN THE BLANK
In a ............ change, new substances are formed.
TRUE \ FALSE
Ammonia is a good oxidizing agent.
What are biocatalysts ?
True or false
New substances are formed in a chemical change.
Fill in the blank
A change in which the substance can be brought back to its original state is called a _______ change.
Name the type of chemical reaction shown by the following equation:
CaCO3 → CaO + CO2
Write the chemical reaction where the following changes are observed.
Colour change is noticed
When hydrogen burns in oxygen, water is formed; when electricity is passed through water, hydrogen and oxygen are given out. Name the type of chemical change involved in the two cases.
Name: A greenish-yellow gas.
On heating which of the following substances i.e. copper carbonate, zinc carbonate, washing soda, copper sulphate, zinc nitrate, copper nitrate, lead nitrate, ammonium chloride and ammonium dichromate – relate to the reaction given below.
A coloured substance which leaves a black residue and evolves two gases one of which is acidic and coloured and the other neutral and colourless.
A chemical reaction is often accompanied by external indications or characteristics.
Assertion: The formation of iron oxide from iron is a chemical change.
Reason: For the rust to form from iron, it must be exposed to air and water.
Match the following:
| 1. | Sodium Chloride | a. | CaSO41/2H2O |
| 2. | Calcium sulphate dihydrate | b. | C2H5Oh |
| 3. | Magnesium sulphate hydrate | c. | CaSO4.2H2O |
| 4. | Calcium sulphate hemihydrate | d. | NaCl |
| 5. | Phenol | e. | MgSO4.H2O |
Classify each of the following, as a physical or a chemical change. Give reasons.
(a) Drying of a shirt in the sun.
(b) Rising of hot air over a radiator.
(c) Burning of kerosene in a lantern.
(d) Change the colour of black tea by adding lemon juice to it.
(e) Churning of milk cream to get butter.
Which of the following statement is incorrect for a chemical reaction?
Give two examples for the following case:
Chemical changes
The chemical formula of rust is ______.
Photosynthesis is a chemical charge. Justify your answer.
