Chemistry

Chemical Reactions and Equations

684 Questions

Chemical reactions and equations form a foundational chemistry topic where students identify reaction products, balance chemical formulas, and classify reaction types. It covers critical mechanisms like Markovnikov's rule, precipitation, and endothermic or exothermic processes. These questions are highly common in general science sections of state and central government competitive exams.

Endothermic reactionsPrecipitation reactionsDehydrohalogenation of alkyl halidesChemical equation balancingReaction product identification

Chemical Reactions and Equations Questions

Multiple choice distinction between pairs of amines organic compounds containing nitrogen organic compounds with functional group containing nitrogen chemistry

A compound $(X)$ with molecular formula $C _3H _9N$ react with $C _6H _5SO _2Cl$ to give a solid which is insoluble in alkali. $(X)$ is:

  1. $CH _3CH _2CH _2NH _2$
  2. $CH _3 - {\underset{CH _3}{\underset{|}{\overset{CH _3}{\overset{|}{N:}}}}}$
  3. $CH _3 - NH - CH _2CH _3$
  4. $CH _3 - {\underset{CH _3}{\underset{|}{CH}}} - NH _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Since the compound reacts with benzenesulphonyl chloride to give a product which is insoluble in alkali, it shows there is no $H$ attached to $N$ in the product . Hence, the compound $X$ is a secondary amine.
$CH _3 - NH - C-2H _5 + C _6H _5SO _2Cl \rightarrow \underset{N - Ethyl - N - methylbenzene sulphonamide}{CH _3 - {\underset{C _2H _5}{\underset{|}{N}}} - SO _2C _6H _5}$

Multiple choice distinction between pairs of amines organic compounds containing nitrogen organic compounds with functional group containing nitrogen chemistry

During preparation of arene diazonium salts, the excess of nitrous acid, if any, is destroyed by adding?

  1. $aq. \, NaOH$
  2. $aq. \, Na _2CO _3$
  3. $aq. \, NH _2CONH _2$
  4. $aq. \, KI$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Urea decomposes $HNO _2$ to give $N _2, \, CO _2 $ and $ H _2O$
$NH _2CONH _2+\, 2HONO \rightarrow 2N _2 \uparrow + \, CO _2 \uparrow +\, 3H _2O$

Multiple choice chemistry measurement and data processing and analysis spectroscopic identification of organic compounds materials science introduction superconducting metals and x-ray crystallography

Which of the following is not a nucleophile :

  1. $CH _3O^-$
  2. $H _2O$
  3. $CH _3-OCH _3$
  4. $CH _3-\underset{H}{\underset{|}{\overset{+}{O}}} - H$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Nucleophile are electron rich species, can donate their electron SO, $CH _3-\underset{H}{\underset{|}{\overset{+}{O}}} - H$ is not a Nucleophile.

Multiple choice chemistry derivatives of hydrocarbons alcohol nomenclature of alcohols and phenols introduction to alcohols

Identify 'C' in the following reaction. 


$C _2H _5Br       \overset{KCN}  {\longrightarrow} A \overset{H^+ H _2O}   {\longrightarrow} B \overset{LiAlH _4}{\longrightarrow} C$

  1. $Propan - 1 - ol$
  2. $Propanone$
  3. $2 - Ethyl - 3 - pentanone$
  4. $Propanal$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

C2H5Br + KCN -> C2H5CN (Propanenitrile). Hydrolysis -> C2H5COOH (Propanoic acid). Reduction with LiAlH4 -> C2H5CH2OH (Propan-1-ol).

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

The overall reaction of a hydrogen-oxygen fuel cell is:

  1. $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$
  2. $2H _{2(g)}+4OH^- _{(aq)}\rightarrow 4H _2O _{(l)}+4e^-$
  3. $O _{2(g)}+2H _2O _{(l)}+4e^-\rightarrow 4OH^- _{(aq)}$
  4. $4OH^- _{(aq)}+4e^-\rightarrow 2H _2O _{(l)}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
A fuel cell is an electrochemical cell that converts the chemical energy from a fuel into electricity through an electrochemical reaction of hydrogen fuelwith oxygen or anotheroxidizing agent.
The reactions which takes place in hydrogen-oxygen fuel cell are,
At cathode:$2H _{2(g)}+4OH^{-} _{(aq)}\rightarrow 4H _2O _{(l)}+4e^{-}$
At cathode:$O _{2(g)}+2H _2O _{(l)}+4e^{-}\rightarrow 4OH^{-} _{(aq)}$
Overall reaction: $2H _{2(g)}+O _{2(g)}\rightarrow 2H _2O _{(l)}$

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

Identify the reaction taking place at cathode in fuel cell.

  1. ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}$
  2. $2{H} _{2}+4{OH}^{-}\rightarrow 4{H} _{2}O+4{e}^{-}$
  3. ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}+{H}^{+}$
  4. $4{H} _{2}O+4{e}^{-}\rightarrow 2{H}^{2}+4{OH}^{-}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a fuel cell the hydrogen enters the fuel cell at the anode. A chemical reaction strips the hydrogen molecules of their electrons and the atoms become ionized to form $H^+$. The electrons travel through wires to provide a current to do work. The oxygen enters at the cathode, usually from the air. The oxygen picks up the electrons that have completed their circuit. The oxygen then combines with the ionized hydrogen atoms $(H^+)$, and water $(H _2O)$ is formed as the waste product which exits the fuel cell. 
Cathode side (a reduction reaction): $O _2 + 4H^+ + 4e^- \rightarrow 2H _2O$
or ${O} _{2}+2{H} _{2}O+4{e}^{-}\rightarrow 4{OH}^{-}$

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

Which of the following reactions is used to make a fuel cell?

  1. $Cd(s) + 2Ni(OH) _{3} (s) \rightarrow CdO(s) + 2Ni(OH) _{2} (s) + H _{2}O(l)$
  2. $Pb(s) + PbO _{2}(s) + 2H _{2} SO _{4}(aq) \rightarrow 2PbSO _{4}(s) + 2H _{2}O(l)$
  3. $2H _{2}(g) + O _{2}(g) \rightarrow 2H _{2}O(l)$
  4. $2Fe(s) + O _{2}(g) + 4H^{+} (aq) \rightarrow 2Fe^{2+}(aq) + 2H _{2}O(l)$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Reaction used in fuel cell is
$2H _{2}(g) + O _{2}(g) \rightarrow 2H _{2}O (l)$

At anode: $[H _{2} \rightarrow 2H^{+} + 2e]\times 2$
At cathode: $O _{2} + 2H _{2}O + 4e\rightarrow 4OH^{-}$

Hence, option C is correct.

Multiple choice chemistry energy fuel cell fuel cells electrochemistry, rechargeable batteries, and fuel cells

Fuel cell involves which of the following reaction(s) ?

  1. $O _{2}(g) + 2H _{2}O(l) + 4e^{-} \rightarrow 4OH^{-}(aq.)$ (at cathode)
  2. $O _{2}(g) + 2H _{2}O(l) + 4e^{-}\rightarrow 4OH^{-}(aq.)$ (at anode)
  3. $2H _{2}(g) + 4OH^{-}(aq.) \rightarrow 4H _{2}O(l) + 4e^{-}$ (at anode)
  4. $2H _{2}(g) + 4OH^{-}(aq.) \rightarrow 4H _{2}O(l) + 4e^{-}$ (at cathode)
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

Question approach,

at anode- loss of electron takes place,
at cathode- gain of electron takes place,
in option B, at anode gain of electron is talking place and in option D at cathode, loss of elctron is taking place;
so, both these statements are wrong
option A and C are representing the Hydrogen fuel cell reactions
hence, both A and C are correct options. 

Multiple choice law of reciprocal proportion laws of chemical combination basic concepts of chemistry some basic concepts of chemistry chemistry

$A$ g of sulphur and $ B$ g of oxygen are allowed to react to form $SO _2 $. What will be the ratio of $ A:B$ ?

  1. $1:1$
  2. $1:2$
  3. $1:3$
  4. $1:4$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$S\left( 32ℊ \right) +{ O } _{ 2 }\left( \left( 16\times 2 \right) ℊ \right) \longrightarrow S{ O } _{ 2 }$
$\Rightarrow $Ratio of A and B is $1:1$
Multiple choice chemistry substances in common use salts and their properties study of some important salts salts used in daily life

Reaction, $Cl _2 + 2NaOH \rightarrow P$            

What are the products?

  1. $NaCl + NaOCl + H _2$
  2. $NaCl + NaOCl + H _2O _2$
  3. $NaCl + NaOCl + H _2O$
  4. $NaCl + NaOCl + O _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The reaction of non-metals with bases is complex. Example: When chlorine reacts with a base like sodium hydroxide, it gives multiple products like sodium hypochlorite, sodium chloride and water.

$Cl _2 + 2NaOH \rightarrow NaCl + NaOCl + H _2O$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

Which of the following is pseudo-unimolecular reaction?

  1. $2{ H } _{ 2 }{ O } _{ 2 }\longrightarrow 2{ H } _{ 2 }O+{ O } _{ 2 }$
  2. ${ C } _{ 6 }{ H } _{ 5 }{ N } _{ 2 }Cl+HOH\longrightarrow { C } _{ 6 }{ H } _{ 5 }OH+{ N } _{ 2 }+HCl$
  3. $C{ H } _{ 3 }COO{ C } _{ 2 }{ H } _{ 5 }+NaOH\longrightarrow C{ H } _{ 3 }COONa+{ C } _{ 2 }{ H } _{ 5 }OH$
  4. $2{ O } _{ 3 }\longrightarrow 3{ O } _{ 2 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In a chemical reaction if two or more reactants are involved but the rate of reaction depends only upon the concentration of one of the reactant and independent of other reactants then it is said to be a pseudo unimolecular reaction.

so the option B shows the pseudotype of reaction 

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

Which of the following are pseudo unimolecular reactions?

  1. $C{ H } _{ 3 }COO{ C } _{ 2 }{ H } _{ 5 }+HOH\xrightarrow [ ]{ \quad { H }^{ + }\quad } C{ H } _{ 3 }COOH+{ C } _{ 2 }{ H } _{ 5 }OH$
  2. $C{ H } _{ 3 }COO{ C } _{ 2 }{ H } _{ 5 }+HOH\xrightarrow [ ]{ \quad O{ H }^{ - }\quad } C{ H } _{ 3 }COOH+{ C } _{ 2 }{ H } _{ 5 }OH$
  3. $\begin{matrix} { C } _{ 12 }{ H } _{ 22 }{ O } _{ 11 } \\ \end{matrix}\begin{matrix} +HOH \\ \end{matrix}\begin{matrix} \xrightarrow [ ]{ \quad { H }^{ + }\quad } \\ \end{matrix}\begin{matrix} { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 } \\ glucose \end{matrix}\begin{matrix} + \\ \end{matrix}\begin{matrix} { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 } \\ fructose \end{matrix}$
  4. $S{ O } _{ 2 }{ Cl } _{ 2 }\left( g \right) \longrightarrow S{ O } _{ 2 }\left( g \right) +{ Cl } _{ 2 }\left( g \right) $
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

In a chemical reaction if two or more reactants are involved but the rate of reaction depends only upon the concentration of one of the reactant and independent of other reactants

$C{ H } _{ 3 }COO{ C } _{ 2 }{ H } _{ 5 }+HOH\xrightarrow [ ]{ \quad { H }^{ + }\quad } C{ H } _{ 3 }COOH+{ C } _{ 2 }{ H } _{ 5 }OH$

$\begin{matrix} { C } _{ 12 }{ H } _{ 22 }{ O } _{ 11 } \ \end{matrix}\begin{matrix} +HOH \ \end{matrix}\begin{matrix} \xrightarrow [ ]{ \quad { H }^{ + }\quad } \ \end{matrix}\begin{matrix} { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 } \ glucose \end{matrix}\begin{matrix} + \ \end{matrix}\begin{matrix} { C } _{ 6 }{ H } _{ 12 }{ O } _{ 6 } \ fructose \end{matrix}$ 
is unimolecular reaction 

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

Which of the following is/are examples of pseudo unimolecular reactions ?

  1. $\displaystyle CH _3CO _2C _2H _5\, +\, H _2O\, \overset{H^{\oplus}}{\rightarrow}\, CH _3CO _2H\, +\, C _2H _5OH$
  2. $\displaystyle C _{12}H _{22}O _{11}\, +\, H _2O\, \overset{H^{\oplus}}{\rightarrow}\, \begin{matrix} & C _6H _{12}O _6\\ & (Glucose)\end{matrix}\, =\, \begin{matrix} & C _6H _{12}O _6\\ & (Fructose)\end{matrix}$
  3. $CH _3COCl\, +\, H _2O\, \rightarrow\, CH _3CO _2H\, +\, HCl$
  4. $\displaystyle CH _3CO _2C _2H _5\, +\, H _2O\, \overset{OH^{\oplus}}{\rightarrow}\, CH _3CO _2H\, +\, C _2H _5OH$
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

The reactions of the options A, B and C represents pseudo unimolecular reactions as water is present in large excess. Hence, the concentration of water remains practically unchanged and does not affect the rate of the reaction.  

Hydrolysis of ester in acidic medium is pseudo unimolecular and in alkaline medium is bimolecular. Inversion of cane sugar and the hydrolysis of acetyl chloride is also pseudo unimolecular.