Chemistry

Chemical Reactions and Processes

571 Questions

Chemical reactions and processes questions cover the transformation of substances through electrolysis, thermal decomposition, and catalysis. Key areas include identifying gas evolution, balancing chemical equations, and understanding industrial chemical applications. This general chemistry topic is a staple in the science sections of multiple competitive examinations.

Thermal decompositionElectrolysis processGas evolution reactionsHeterogeneous catalystsFuel cell components

Chemical Reactions and Processes Questions

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

When hydrogen and oxygen combine to form water, they form:

  1. an unstable compound

  2. a stable mixture

  3. an unstable mixture

  4. an extremely stable compound
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When hydrogen and oxygen combine to form water, they form water an extremely stable compound. We can say water is a stable compound because tremendous energy is released is a signal that hydrogen and oxygen are very eager to become water or in another way it is very hard to break water molecules apart into its components.

$2H _2+O _2\longrightarrow 2H _2O$

Multiple choice evs let's play with water law of constant proportion - i law of constant proportion law of definite proportions

If you put a waterproof, nine-volt battery in a mug of water containing two teaspoonfuls of salt, the water will be broken into gases and bubbles will start forming. What are these gases?

  1. Carbon dioxide and nitrogen

  2. Hydrogen and oxygen

  3. Fluorine and chlorine

  4. Sulphur dioxide and 'laughing gas'
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Water will start comparing electrostatically,


$2H _2O \underset{electroysis}{\rightarrow} 2H _2+O _2$


These gases are hydrogen and oxygen.

Multiple choice chemistry general principles of metallurgy extraction of copper and zinc extraction of copper and zinc from their oxides basics of metallurgy

A brown and bright element 'X' when heated in presence of air turns into black substance 'Y'. If hydrogen gas is passed over this heating material again 'X' is obtained 'X' and 'Y' are -

  1. Cu & CuO
  2. S & $SO _2$
  3. C & $CO _2$

  4. Na & NaH
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$2 Cu + O _2\xrightarrow {(\Delta)} 2CuO$
(x)                            (y)
Brown & Bright         Black
$CuO + H _2 \rightarrow Cu + H _2O$

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

During hydrogenation reaction, H-H bond splits and hydrogen atoms are attached to Ni catalyst through through strong chemical forces.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In hydrogenation reaction, the H-H bond splits and the hydrogen atom is chemically bonded to the Ni catalyst.

Here the Ni catalyst provides the surface on which reaction takes place.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

The decomposition of hydrogen peroxide can be slowed down by the addition of a small amount of acetamide. The added acetamide acts as:

  1. inhibitor

  2. promoter

  3. moderator

  4. poison
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The chemical substance added to another substance, to slow down a reaction or to prevent an unwanted chemical change is called inhibitor. The decomposition of hydrogen peroxide. Unwanted chemical change can be slowed down by the addition of a small amount of acetamide. The latter acts as an inhibitor.

Multiple choice enzymes and catalysts catalysis adsorption and colloids surface chemistry chemistry adsorption theory of heterogeneous catalysis

Which are not examples of autocatalysis?

  1. Breakdown of atomic fuel in reactor.

  2. Shock decomposition of glycerol trinitrate.

  3. ZSM-5 used to convert alcohol in petrol.

  4. Storage of chloroform along with little ethanol.
Reveal answer Fill a bubble to check yourself
A,C,D Correct answer
Explanation

A chemical reaction is said to have undergone autocatalysis if the reaction product itself is the catalyst for that reaction.
Shock decomposition of glycerol trinitrate is autocatalysis due to the mixture of gases which acts as autocatalyst. The reaction is as follows:
$4C _3 H _5 (ONO _2) _3 \rightarrow 12CO _2 + 10H _2O + 6N _2 +O _2$

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

State True or False.
Electrolysis of H$ _2$O gives H$ _2$ at the anode.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The given statement is false.
The electrolysis of $H _2O$ is explained below:
Cathode (reduction):
$2 H _2O(l) + 2e^- \rightarrow  H _2(g) + 2 OH^-(aq)$
Anode (oxidation):
$ 4 OH^-(aq) \rightarrow O _2(g) + 2 H _2O(l) + 4 e^-$
Thus the electrolysis of $H _2O$ gives $H _2$ at the cathode.
Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

______ is prepared by the electrolysis of molten $KHF _2$ and anhydrous $HF$.

  1. $H _2$
  2. Solid $K$
  3. $F _2$

  4. none of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Moissan in 1896 prepared $F _2$ as :
$KHF _2 \rightleftharpoons KF + HF$
$KF \rightleftharpoons  K^{\oplus} + F^{\ominus}$
At anode : $2F^{\ominus} \rightarrow F _2 + 2e^{-}$
At cathode : $K^{\oplus} + e^{-} \rightarrow K$
$K + 2HF \rightarrow 2KF + F _2$

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

During electrolysis of fused calcium hydride, the hydrogen is produced at:

  1. cathode

  2. anode

  3. hydrogen is not liberated at all
  4. $H _2$ produced reacts with oxygen to form water
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$CaH _2\, \xrightarrow {Electrolysis}\, Ca^{2+}\, +\, 2H^{-}$


At cathode (reduction) :
$Ca^{2+}\, +\, 2e^-\, \rightarrow\, Ca$

At anode (oxidation) :
$2H^{-}\, \rightarrow\, H _2\, +\, 2e^-$

At the anode, hydrogen is produced. 

Hence, option $B$ is correct.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Which of the following does not evolve oxygen at anode when the electrolysis is carried out of:

  1. Dilute $H _{2}SO _{4}$ with $Pt$ electrodes
  2. Fused sodium hydroxide with $Pt$ electrodes
  3. Acidic water with $Pt$ electrodes
  4. Dilute sulphuric acid using $Cu$ electrodes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$E^{\ominus} _{ox}$ of $Cu$ =$ - 0.34 $
Using copper electrodes, copper will oxidize : 
$Cu\, \rightarrow\, Cu^{2+}\, +\, 2e^{-}$
So oxygen is not evolved.

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

In Hall's process, in the production of Al, carbon is used as the anode material. The reactions are:

  1. Anode: $Al^3+3e^-\, \rightarrow\, Al$

    Cathode: $C(s)+2O^{2-}\, \rightarrow\, CO _2(s)\, +\, 4e^-$
  2. Anode: $C(s)+2O^{2-}\, \rightarrow\, CO _2(s)\, +\, 4e^-$

    Cathode: $Al^3+3e^-\, \rightarrow\, Al$
  3. Anode: $Al\, \rightarrow\, Ae^{3+}\, +\, e^-$

    Cathode: $CO _2\, +\, 4e^-\, \rightarrow\, C(s)\, +\, 2O^2$

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the production of Al (in Hall's process), reactions are:
Cathode:
$Al^{3+}\, +\, 3e^-\, \rightarrow\, Al$
Anode:
$2O^{-2}\, \rightarrow\, O _2\, +\, 4e^-$
$C\, +\, O _2\, \rightarrow\, CO _2$

Multiple choice chemistry chemical changes electrochemical reactions electrolysis and its applications electrolytic cells and electrolysis

Name the process from which chlorine is obtained as by product. What will happen if an aqueous solution of NaCl is subjected to electrolysis.

  1. Haber process, $NaOH, H _2, Cl _2$
  2. Down cell process, Na metal and $Cl _2$ gas are obtained
  3. Down cell process, $NaOH, H _2, Cl _2$

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Haber process is used for producing ammonia from nitrogen and hydrogen.
Down's Process. Molten NaCl upon electrolysis will give Na metal and $Cl _2$ gas. Aqueous NaCl will form NaOH,$H _2 , Cl _2$.