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प्रश्न
What are (i) positive catalysts and (ii) negative catalysts? Support your answer with one example for each of them.
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उत्तर
(i) Positive catalyst: When a catalyst increases the rate of chemical reaction, it is called positive catalyst.
e.g. when potassium chlorate heated to 700°C decomposes to evolve oxygen gas, when MnO2is added the decomposition takes place at 300°C
\[\ce{2KCIO3->[MnO2][300°C] 2KCl + 3O2}\]
(ii) Negative catalyst: When a catalyst decreases the rate of chemical reaction it is called negative catalyst.
Example. Phosphoric acid acts as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide. Alcohol too acts as a negative catalyst in certain chemical reactions.
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संबंधित प्रश्न
FILL IN THE BLANK
A .............. change is a temporary change.
Fill in the blank
A change in which the substance can be brought back to its original state is called a _______ change.
Copper carbonate when heated, it turns :
Complete the statement by filling the gaps using 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)
Electron ______ is complete in each hydrogen in a hydrogen molecule.
Complete the statement by filling the gaps using 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)
Chlorine (Cl2) molecule is formed by ______ of electrons between two chlorine atoms.
Give an example of the following chemical change.
Two gases combine to form white solid
Write the chemical reaction where the following changes are observed.
Physical state is changed
Multiple choice:
Which of the following is not a characteristic of a chemical change?
Name: Two carbonates do not produce carbon dioxide on heating.
State the original colour of the following substance and colour of residue obtained after heating.
Ammonium dichromate
What do you observe when dilute sulphuric acid is added to the following:
Sodium Sulphide
Explain the term ‘chemical reaction’ with special reference to – ‘reactants’ and ‘products’.
Select the correct answer for the following options:
The black residue obtained on heating copper carbonate.
Give balanced equation for the following conversion affected by heat alone on the substance:
Zinc nitrate to nitrogen dioxide
State the following reaction represent oxidation or reduction.
\[\ce{Cu++->Cu}\]
Can a nickel spatula be used to stir copper sulphate solution? Justify your answer.
A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?
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.
Give an example of a chemical reaction for the following situation:
A change in colour is observed
Write the equation for the process of formation of rust.
