Mix Examples - Chemical Reactions and Equations Questions in English

(C) Corrosion is the process where metals are eaten away by the action of air, moisture, or chemicals.
$1$. Iron $(Fe)$ reacts with oxygen and moisture to form hydrated iron$(III)$ oxide $(Fe_2O_3 \cdot xH_2O)$, which is brown in colour (rust).
$2$. Silver $(Ag)$ reacts with sulfur compounds in the air to form silver sulfide $(Ag_2S)$, which is black in colour (tarnish).
$3$. Copper $(Cu)$ reacts with moist carbon dioxide in the air to form a green coating of basic copper carbonate $(CuCO_3 \cdot Cu(OH)_2)$.
Therefore, the order of colours for iron, silver, and copper is brown, black, and green respectively.

(D) When fats and oils are exposed to air,they undergo oxidation.
This process is known as rancidity.
During oxidation,the chemical structure of fats and oils changes,leading to the development of an unpleasant odor and a foul taste.
Therefore,they become rancid and their smell and taste change.

(A) Substances that are easily oxidised (like fats and oils in food) undergo rancidity when exposed to oxygen.
To prevent this,food items are flushed with an inert gas like $N_2$ (nitrogen) to displace oxygen.
Additionally,keeping them in airtight containers prevents further contact with atmospheric oxygen,thereby extending their shelf life.

(B) When copper powder is heated in a china dish, it reacts with atmospheric oxygen to form copper $(II)$ oxide $(CuO)$.
The chemical reaction is: $2Cu(s) + O_2(g) \xrightarrow{\Delta} 2CuO(s)$.
Copper $(II)$ oxide is a black-coloured compound.
Therefore, the surface of the copper powder turns black.

(C) When hydrogen gas is passed over heated copper oxide $(CuO)$, a redox reaction occurs.
In this reaction, hydrogen reduces copper oxide to copper metal.
The chemical equation for this reaction is: $CuO(s) + H_2(g) \xrightarrow{\Delta} Cu(s) + H_2O(g)$.
Copper oxide $(CuO)$ is black in color, while the copper metal $(Cu)$ formed is reddish-brown in color.
Therefore, the black coating on the surface turns brown.

(D) Black and white photography utilizes the light-sensitive nature of silver halides.
When silver bromide $(AgBr)$ is exposed to sunlight,it undergoes a photochemical decomposition reaction.
The reaction is: $2 AgBr(s) \xrightarrow{\text{Sunlight}} 2 Ag(s) + Br_{2}(g)$.
In this process,silver bromide decomposes into metallic silver $(Ag)$ and bromine gas $(Br_{2})$,which creates the image on the photographic film.

(A) $1$. In the given reaction,$4 NH_{3} + 5 O_{2} \longrightarrow 4 NO + 6 H_{2}O$,the oxidation state of Nitrogen $(N)$ changes from $-3$ in $NH_{3}$ to $+2$ in $NO$ (oxidation).
$2$. The oxidation state of Oxygen $(O)$ changes from $0$ in $O_{2}$ to $-2$ in $NO$ and $H_{2}O$ (reduction).
$3$. Since both oxidation and reduction occur simultaneously,it is a redox reaction $(iii)$.
$4$. This is also a displacement reaction $(i)$ because the oxygen atom displaces hydrogen from ammonia to form water.
$5$. Therefore,the reaction is both a displacement reaction and a redox reaction.

(B) In the given reaction: $3 Fe (s) + 4 H_2 O (g) \longrightarrow Fe_3 O_4 (s) + 4 H_2 (g)$
$1$. Iron $(Fe)$ gains oxygen to form $Fe_3 O_4$,which means iron is getting oxidised.
$2$. Water $(H_2 O)$ loses oxygen to form $H_2$,which means water is getting reduced.
$3$. Since water provides oxygen for the oxidation of iron,it acts as an oxidising agent.
$4$. Therefore,statements $(i)$,$(ii)$,and $(iv)$ are correct.

(C) An exothermic process is a reaction or process that releases energy in the form of heat.
$(i)$ The reaction of water with quicklime $(CaO + H_2O \rightarrow Ca(OH)_2 + \text{Heat})$ is highly exothermic, releasing a significant amount of heat.
$(ii)$ The dilution of an acid is a highly exothermic process, which is why it is recommended to add acid to water slowly with constant stirring.
$(iii)$ Evaporation of water is an endothermic process because it requires the absorption of heat from the surroundings to change the state from liquid to gas.
$(iv)$ Sublimation of camphor is an endothermic process as it requires the absorption of heat to change the state from solid to gas.
Therefore, $(i)$ and $(ii)$ are exothermic processes.

(D) The reaction between acidified potassium permanganate $(KMnO_4)$ and ferrous sulphate $(FeSO_4)$ is a classic redox reaction.
In this reaction,$KMnO_4$ acts as a strong oxidising agent.
It oxidises the ferrous ions $(Fe^{2+})$ present in the $FeSO_4$ solution to ferric ions $(Fe^{3+})$.
During this process,the purple-coloured permanganate ions $(MnO_4^-)$ are reduced to colourless manganese ions $(Mn^{2+})$.
As the concentration of $MnO_4^-$ decreases,the purple colour of the solution fades and eventually disappears.

(A) double displacement reaction is a chemical reaction where two reactant ionic compounds exchange ions to form two new products.
Analysis of the given reactions:
$(i)$ $Pb + CuCl_2 \longrightarrow PbCl_2 + Cu$: This is a displacement reaction where $Pb$ displaces $Cu$.
$(ii)$ $Na_2SO_4 + BaCl_2 \longrightarrow BaSO_4 + 2NaCl$: This is a double displacement reaction where $Na^+$ and $Ba^{2+}$ ions exchange places.
$(iii)$ $C + O_2 \longrightarrow CO_2$: This is a combination reaction.
$(iv)$ $CH_4 + 2O_2 \longrightarrow CO_2 + 2H_2O$: This is a combustion reaction.
Therefore,only reaction $(ii)$ is a double displacement reaction.

(A) Silver chloride $(AgCl)$ is a light-sensitive compound.
When exposed to sunlight,it undergoes a photochemical decomposition reaction.
The chemical equation for this reaction is: $2AgCl(s) \xrightarrow{sunlight} 2Ag(s) + Cl_2(g)$.
In this process,silver chloride decomposes to form metallic silver $(Ag)$,which is grey in color,and chlorine gas $(Cl_2)$ is released.
Therefore,statement $(i)$ is correct because silver is formed,and statement $(iii)$ is correct because chlorine gas is released due to the decomposition of silver chloride.
Thus,both $(i)$ and $(iii)$ are true.

(C) An endothermic process is one that absorbs heat from the surroundings.
$(i)$ Dilution of sulphuric acid is an exothermic process because it releases a large amount of heat.
$(ii)$ Sublimation of dry ice ($CO_2$ solid to gas) requires the absorption of heat,making it an endothermic process.
$(iii)$ Condensation of water vapours (gas to liquid) releases heat,making it an exothermic process.
$(iv)$ Evaporation of water (liquid to gas) requires the absorption of heat from the surroundings,making it an endothermic process.
Therefore,both $(ii)$ and $(iv)$ are endothermic processes.

(D) The reaction between potassium iodide $(KI)$ and lead nitrate $(Pb(NO_3)_2)$ is a double displacement reaction that produces a yellow precipitate of lead iodide $(PbI_2)$.
$2KI(aq) + Pb(NO_3)_2(aq) \rightarrow PbI_2(s) + 2KNO_3(aq)$
To obtain the yellow precipitate of lead iodide,we need a soluble lead salt that can provide lead ions $(Pb^{2+})$ in the aqueous solution.
Lead sulphate is insoluble in water,so it cannot be used.
Potassium sulphate and ammonium nitrate do not contain lead ions.
Lead acetate $(Pb(CH_3COO)_2)$ is a soluble lead salt that dissociates to provide $Pb^{2+}$ ions,which react with iodide ions to form the yellow precipitate of lead iodide. Therefore,lead acetate is the correct substitute.

(C) The reaction between hydrogen and oxygen to form water is a combustion reaction.
At standard reaction temperatures (often involving combustion),hydrogen $(H_2)$ and oxygen $(O_2)$ exist as gases $(g)$.
The product formed,water $(H_2O)$,is typically produced in the liquid state $(l)$ at room temperature or standard conditions following the reaction.
Therefore,the correct representation is $2H_2(g) + O_2(g) \longrightarrow 2H_2O(l)$.

(B) combination reaction is a reaction in which two or more reactants combine to form a single product.
$(i)$ $2 KClO_{3} \longrightarrow 2 KCl + 3O_{2}$ is a decomposition reaction because one reactant breaks down into multiple products.
$(ii)$ $MgO + H_{2}O \longrightarrow Mg(OH)_{2}$ is a combination reaction because two reactants combine to form a single product.
$(iii)$ $4 Al + 3O_{2} \longrightarrow 2 Al_{2}O_{3}$ is a combination reaction because two reactants combine to form a single product.
$(iv)$ $Zn + FeSO_{4} \longrightarrow ZnSO_{4} + Fe$ is a displacement reaction because $Zn$ displaces $Fe$ from its salt solution.
Therefore,$(ii)$ and $(iii)$ are combination reactions.

(A) $(TRUE)$ The statement is $True$. Ferrous sulphate crystals $(FeSO_4 \cdot 7H_2O)$ are light green in colour. Upon heating,they first lose water of crystallisation to become anhydrous ferrous sulphate $(FeSO_4)$,which is white or greyish-white. Further heating leads to the decomposition of ferrous sulphate into ferric oxide $(Fe_2O_3)$,sulphur dioxide $(SO_2)$,and sulphur trioxide $(SO_3)$.

(A) The statement is true.
Calcium oxide,with the chemical formula $CaO$,is commonly known as lime or quicklime. It is produced by the thermal decomposition of limestone $(CaCO_3)$.

(TRUE) The statement is $True$.
When lead nitrate $(Pb(NO_3)_2)$ is heated, it undergoes thermal decomposition to form lead oxide $(PbO)$, nitrogen dioxide $(NO_2)$, and oxygen $(O_2)$.
The chemical equation is: $2Pb(NO_3)_2(s) \xrightarrow{\Delta} 2PbO(s) + 4NO_2(g) + O_2(g)$.
The brown fumes observed are due to the evolution of nitrogen dioxide $(NO_2)$ gas.

(FALSE) The statement is False.
In black and white photography,the decomposition reaction of silver chloride $(AgCl)$ or silver bromide $(AgBr)$ is used,not calcium sulphate.
The reaction is: $2AgCl(s) \xrightarrow{sunlight} 2Ag(s) + Cl_2(g)$.

(FALSE) The statement is False.
Silver bromide $(AgBr)$ undergoes a photochemical decomposition reaction when exposed to light,breaking down into silver $(Ag)$ and bromine $(Br_2)$.
This reaction is primarily used in black and white photography,not in the manufacturing of cement.

(TRUE) The statement is true.
In a chemical reaction,when two solutions are mixed,if an insoluble solid is formed,it is called a precipitate. This type of reaction is known as a precipitation reaction.

(FALSE) False. In an endothermic reaction,heat is absorbed from the surroundings by the reacting substances. Conversely,in an exothermic reaction,heat is released from the reacting substances to the surroundings.

(FALSE) False.
This reaction is an example of a displacement reaction (specifically,a single displacement reaction).
In this reaction,a more reactive metal,$Zn$,displaces a less reactive metal,$Cu$,from its salt solution $(CuSO_4)$.
$A$ double displacement reaction involves the exchange of ions between two reactants,which is not the case here.

(A) The statement is $True$.
Food items containing fats and oils get oxidized when exposed to air, which leads to rancidity, resulting in an unpleasant smell and taste.
By keeping food in airtight containers, the exposure to oxygen is significantly reduced or prevented.
This reduction in oxygen contact slows down the oxidation process, thereby preserving the freshness and quality of the food for a longer period.

(A) The statement is True.
$1$. Iron $(Fe)$ reacts with moisture and oxygen to form hydrated iron$(III)$ oxide $(Fe_2O_3 \cdot xH_2O)$, which is a reddish-brown substance known as rust.
$2$. Copper $(Cu)$ reacts with moist carbon dioxide in the air to form a green coating of basic copper carbonate $(CuCO_3 \cdot Cu(OH)_2)$.
$3$. Silver $(Ag)$ reacts with sulfur compounds in the air (like hydrogen sulfide) to form a black coating of silver sulfide $(Ag_2S)$.