Chemical reactions and equations model test questions

Please refer to notes and solved questions for any query as all questions here are explained there.

Q. Balance a chemical equation of Fe + H2O ———–> Fe3O+ H2 with steps.


Step 1: Balance atoms of elements present in the highest number in the reaction.

e.g. Fe + 4H2O ———–> Fe3O+ H2

Step 2: Balance other elements.

3Fe + 4H2O ———–> Fe3O+ 4H2

Step 3: Check if the equation is balanced. (If not write the value in the factorial form and multiply all number with its denominator)

Step 4: Add the state of the elements and compound formed and conditions. e.g. Solid(s), Liquid(l), Gas(g), Sunlight, Heat

3Fe(s) + 4H2O(l) ———–> Fe3O4(s) + 4H2(g)

Q. Write a short note on the types of chemical reaction with an example.


a. Combination reaction:

CaO(s) + H2O(l) ———-> Ca(OH)2(aq)


Carbon(s) + O2(g) ———-> C02(g)

b. Decomposition reaction


CaCO3(s) —————>   CaO   +   CO2(g)

Limestone                    Quick lime

c. Displacement reactions:

Iron displaces Copper from  Copper sulphate solution(Blue) to form colourless Ferrous sulphate.

Fe(s) + CuSO4(aq) ———–> FeS04(aq) + Cu(s)

d. Double displacement reaction

Take a salt with another salt or a acid with base

2NaS04(aq) + 2BaCl2(aq)  ————–>  2BaS04(s) + 2NaCl(aq)

e. Oxidation- reduction reaction

Oxidation: Copper on heating combines with oxygen to form its oxide(Black).


2Cu(s) + O2  ———-> 2CuO(s)

Reduction: Copper oxide on heating in presence of hydrogen gas yields pure copper

Q. What is corrosion.

Hint: Rusting of iron, Blackening of silver, copper.

Q. What is rancidity? How is it prevented?

Hint: Oxidation of fats and oils.

Prevented by use of anti-oxidant, nitrogen gas

Q. Give an example of precipitation reaction.

Hint: Silver nitrate with NaCl, Barium chloride with sodium sulphate.

Q. Why halides of silver like Agcl and AgBr are used in photography?
Q. Give the significance of using quick lime in whitewashing.

Please refer to solved question and notes for any clarification.

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