Textbook - Chemical Reactions and Equations Questions in English

(N/A) $Magnesium$ is a very reactive metal. When stored,it reacts with oxygen to form a layer of $Magnesium$ $Oxide$ $(MgO)$ on its surface. This layer of $Magnesium$ $Oxide$ is quite stable and prevents further reaction of $Magnesium$ with oxygen. The $Magnesium$ ribbon is cleaned with sandpaper to remove this layer so that the underlying metal can be exposed to air for combustion.

(N/A) $(i)$ $H_{2(g)} + Cl_{2(g)} \longrightarrow 2HCl_{(g)}$
$(ii)$ $3BaCl_{2(aq)} + Al_{2}(SO_{4})_{3(aq)} \longrightarrow 3BaSO_{4(s)} + 2AlCl_{3(aq)}$
$(iii)$ $2Na_{(s)} + 2H_{2}O_{(l)} \longrightarrow 2NaOH_{(aq)} + H_{2(g)}$

(N/A) $(i)$ The reaction between barium chloride and sodium sulphate is a double displacement reaction:
$BaCl_{2(aq)} + Na_2SO_{4(aq)} \to BaSO_{4(s)} + 2NaCl_{(aq)}$
$(ii)$ The reaction between sodium hydroxide and hydrochloric acid is a neutralization reaction:
$NaOH_{(aq)} + HCl_{(aq)} \to NaCl_{(aq)} + H_2O_{(l)}$

(N/A) $(i)$ The substance $X$ is calcium oxide. Its chemical formula is $CaO$.
$(ii)$ Calcium oxide reacts vigorously with water to form calcium hydroxide (slaked lime).
The chemical reaction is:
$CaO_{(s)} + H_2O_{(l)} \to Ca(OH)_{2(aq)}$
Where $CaO$ is Calcium oxide (Quick lime) and $Ca(OH)_2$ is Calcium hydroxide (Slaked lime).

(N/A) Water $(H_2O)$ consists of two parts hydrogen and one part oxygen by volume.
During the electrolysis of water,the chemical reaction is: $2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$.
This reaction shows that hydrogen gas and oxygen gas are produced in a $2:1$ ratio.
Since hydrogen gas is collected at the cathode and oxygen gas is collected at the anode,the volume of hydrogen collected is double the volume of oxygen collected.
The gas collected in double the amount is hydrogen.

(N/A) When an iron nail is placed in a copper sulphate solution,iron being more reactive than copper,displaces copper from the copper sulphate solution. This reaction forms iron sulphate,which is green in colour.
$Fe_{(s)} + CuSO_{4(aq)} \rightarrow FeSO_{4(aq)} + Cu_{(s)}$
In this reaction,the blue colour of the copper sulphate solution fades as it is converted into light green iron sulphate solution,and a reddish-brown deposit of copper is formed on the iron nail.

(N/A) Sodium carbonate reacts with calcium chloride to form calcium carbonate and sodium chloride.
$Na_{2}CO_{3(aq)} + CaCl_{2(aq)} \to CaCO_{3(s)} + 2NaCl_{(aq)}$
In this reaction,sodium carbonate and calcium chloride exchange ions to form two new compounds. Hence,it is a double displacement reaction.

(A) $(i)$ In the reaction $4Na(s) + O_2(g) \rightarrow 2Na_2O(s)$,Sodium $(Na)$ is oxidised because it gains oxygen to form $Na_2O$,and Oxygen $(O_2)$ is reduced.
$(ii)$ In the reaction $CuO(s) + H_2(g) \rightarrow Cu(s) + H_2O(l)$,Copper oxide $(CuO)$ is reduced to Copper $(Cu)$ because it loses oxygen,while Hydrogen $(H_2)$ is oxidised to Water $(H_2O)$ because it gains oxygen.

(A) In the given reaction: $2 PbO_{(s)} + C_{(s)} \longrightarrow 2 Pb_{(s)} + CO_{2(g)}$
$1$. Lead oxide $(PbO)$ loses oxygen to form lead $(Pb)$,so $PbO$ is being reduced.
$2$. Carbon $(C)$ gains oxygen to form carbon dioxide $(CO_2)$,so $C$ is being oxidised.
Evaluating the statements:
$(a)$ Lead is getting reduced: Incorrect. Lead oxide is being reduced,not lead.
$(b)$ Carbon dioxide is getting oxidised: Incorrect. Carbon is being oxidised to form carbon dioxide.
$(c)$ Carbon is getting oxidised: Correct.
$(d)$ Lead oxide is getting reduced: Correct.
Therefore,statements $(a)$ and $(b)$ are incorrect.

(B) In the given chemical reaction,$Al$ (aluminum) is more reactive than $Fe$ (iron).
Therefore,$Al$ displaces $Fe$ from its oxide $(Fe_{2}O_{3})$.
This type of reaction,where a more reactive element displaces a less reactive element from its compound,is known as a displacement reaction.
Specifically,this is a thermite reaction.

(C) When dilute hydrochloric acid $(HCl)$ is added to iron $(Fe)$ filings,a displacement reaction occurs where iron displaces hydrogen from the acid.
This results in the formation of iron$(II)$ chloride $(FeCl_2)$ and the evolution of hydrogen gas $(H_2)$.
The chemical equation for this reaction is:
$Fe_{(s)} + 2HCl_{(aq)} \to FeCl_{2(aq)} + H_{2(g)} \uparrow$

(N/A) balanced chemical equation is one in which the number of atoms of each element is equal on both the reactant and product sides.
Chemical equations must be balanced to satisfy the $Law$ of $Conservation$ of $Mass$. This law states that mass can neither be created nor destroyed in a chemical reaction. Therefore,the total mass of the elements present in the reactants must be equal to the total mass of the elements present in the products. To ensure this,the number of atoms of each element must be the same on both sides of the equation.

(A) The reaction is $H_{2(g)} + N_{2(g)} \to NH_{3(g)}$. Balancing gives $3H_{2(g)} + N_{2(g)} \to 2NH_{3(g)}$.
$(b)$ The reaction is $H_{2}S_{(g)} + O_{2(g)} \to H_{2}O_{(l)} + SO_{2(g)}$. Balancing gives $2H_{2}S_{(g)} + 3O_{2(g)} \to 2H_{2}O_{(l)} + 2SO_{2(g)}$.
$(c)$ The reaction is $BaCl_{2(aq)} + Al_{2}(SO_{4})_{3(aq)} \to AlCl_{3(aq)} + BaSO_{4(s)}$. Balancing gives $3BaCl_{2(aq)} + Al_{2}(SO_{4})_{3(aq)} \to 2AlCl_{3(aq)} + 3BaSO_{4(s)}$.
$(d)$ The reaction is $K_{(s)} + H_{2}O_{(l)} \to KOH_{(aq)} + H_{2(g)}$. Balancing gives $2K_{(s)} + 2H_{2}O_{(l)} \to 2KOH_{(aq)} + H_{2(g)}$.

(A) To balance a chemical equation,the number of atoms of each element must be equal on both the reactant and product sides.
$(a)$ $2HNO_{3} + Ca(OH)_{2} \longrightarrow Ca(NO_{3})_{2} + 2H_{2}O$
Here,there are $2$ $N$ atoms,$8$ $O$ atoms,$4$ $H$ atoms,and $1$ $Ca$ atom on both sides.
$(b)$ $2NaOH + H_{2}SO_{4} \longrightarrow Na_{2}SO_{4} + 2H_{2}O$
Here,there are $2$ $Na$ atoms,$6$ $O$ atoms,$4$ $H$ atoms,and $1$ $S$ atom on both sides.
$(c)$ $NaCl + AgNO_{3} \longrightarrow AgCl + NaNO_{3}$
This equation is already balanced as the number of atoms of each element is equal on both sides.
$(d)$ $BaCl_{2} + H_{2}SO_{4} \longrightarrow BaSO_{4} + 2HCl$
Here,there is $1$ $Ba$ atom,$2$ $Cl$ atoms,$2$ $H$ atoms,$1$ $S$ atom,and $4$ $O$ atoms on both sides.

(N/A) $Ca(OH)_{2} + CO_{2} \rightarrow CaCO_{3} + H_{2}O$
$(b)$ $Zn + 2AgNO_{3} \rightarrow Zn(NO_{3})_{2} + 2Ag$
$(c)$ $2Al + 3CuCl_{2} \rightarrow 2AlCl_{3} + 3Cu$
$(d)$ $BaCl_{2} + K_{2}SO_{4} \rightarrow BaSO_{4} + 2KCl$

(A-D) $2KBr(aq) + BaI_2(aq) \rightarrow 2KI(aq) + BaBr_2(s)$; Double displacement reaction.
$(b)$ $ZnCO_3(s) \rightarrow ZnO(s) + CO_2(g)$; Decomposition reaction.
$(c)$ $H_2(g) + Cl_2(g) \rightarrow 2HCl(g)$; Combination reaction.
$(d)$ $Mg(s) + 2HCl(aq) \rightarrow MgCl_2(aq) + H_2(g)$; Displacement reaction.

(N/A) Chemical reactions that release energy in the form of heat,light,or sound are called exothermic reactions.
Example: The reaction of sodium and chlorine to yield table salt:
$Na_{(s)} + \frac{1}{2} Cl_{2(g)} \longrightarrow NaCl_{(s)} + 411 \, kJ$ of energy.
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
Example: In the process of photosynthesis,plants use energy from the sun to convert carbon dioxide and water into glucose and oxygen:
$6CO_{2(g)} + 6H_{2}O_{(l)} \xrightarrow{\text{Sunlight}} C_{6}H_{12}O_{6(aq)} + 6O_{2(g)}$

(N/A) Respiration is considered an exothermic reaction because energy is released during the process.
$1$. Living organisms require energy to survive, which is obtained from the food we eat.
$2$. During digestion, complex food molecules (like carbohydrates) are broken down into simpler substances like glucose.
$3$. This glucose combines with oxygen in the cells of our body to provide energy.
$4$. Since energy is released in the form of heat (or $ATP$) during this process, it is classified as an exothermic reaction.
The chemical equation for respiration is:
$C_{6}H_{12}O_{6(aq)} + 6O_{2(g)} \to 6CO_{2(g)} + 6H_{2}O_{(l)} + \text{Energy}$

(N/A) Decomposition reactions are those in which a single compound breaks down to form two or more simpler substances. These reactions typically require an input of energy in the form of heat, light, or electricity to proceed.
Combination reactions are those in which two or more substances combine to form a single new substance, often releasing energy in the process.
Therefore, they are considered opposites because decomposition involves breaking down a substance (requiring energy), while combination involves forming a substance (releasing energy).
Decomposition reaction: $2H_2O(l) \xrightarrow{\text{Electrolysis}} 2H_2(g) + O_2(g)$
Combination reaction: $2H_2(g) + O_2(g) \to 2H_2O(l) + \text{Energy}$

(N/A) Thermal decomposition:
$2FeSO_{4(s)} \xrightarrow{\Delta} Fe_2O_{3(s)} + SO_{2(g)} + SO_{3(g)}$
(Ferrous sulphate $\rightarrow$ Ferric oxide + Sulphur dioxide + Sulphur trioxide)
$(b)$ Photolytic decomposition (by light):
$2AgCl_{(s)} \xrightarrow{\text{Light}} 2Ag_{(s)} + Cl_{2(g)}$
(Silver chloride $\rightarrow$ Silver + Chlorine)
$(c)$ Electrolytic decomposition (by electricity):
$2H_2O_{(l)} \xrightarrow{\text{Electricity}} 2H_{2(g)} + O_{2(g)}$
(Water $\rightarrow$ Hydrogen + Oxygen)

(N/A) In a displacement reaction,a more reactive element replaces a less reactive element from its compound.
$A + BX \longrightarrow AX + B$; where $A$ is more reactive than $B$.
In a double displacement reaction,two atoms or groups of atoms exchange their positions to form two new compounds.
$AB + CD \longrightarrow AD + CB$
Examples:
Displacement reaction:
$CuSO_{4(aq)} + Zn_{(s)} \longrightarrow ZnSO_{4(aq)} + Cu_{(s)}$
Double displacement reaction:
$Na_2SO_{4(aq)} + BaCl_{2(aq)} \longrightarrow BaSO_{4(s)} + 2NaCl_{(aq)}$

(N/A) The recovery of silver from silver nitrate solution by copper metal is a displacement reaction. Copper is more reactive than silver,so it displaces silver from its salt solution.
The chemical reaction is:
$2AgNO_{3(aq)} + Cu_{(s)} \to Cu(NO_3)_{2(aq)} + 2Ag_{(s)}$
In this reaction,copper metal displaces silver ions from the silver nitrate solution to form copper$(II)$ nitrate and solid silver.

(N/A) reaction in which an insoluble solid (called precipitate) is formed is called a precipitation reaction.
For example:
$Na_2CO_{3(aq)} + CaCl_{2(aq)} \to CaCO_{3(s)} + 2NaCl_{(aq)}$
In this reaction,calcium carbonate $(CaCO_3)$ is obtained as a white precipitate.
Another example of a precipitation reaction is:
$Na_2SO_{4(aq)} + BaCl_{2(aq)} \to BaSO_{4(s)} + 2NaCl_{(aq)}$
In this reaction,barium sulphate $(BaSO_4)$ is obtained as a white precipitate.

(N/A) Oxidation is defined as the gain of oxygen by a substance during a chemical reaction.
For example:
$(i)$ $H_2 + CO_2 \rightarrow H_2O + CO$
In this reaction, $H_2$ gains oxygen to form $H_2O$, therefore $H_2$ is oxidized.
$(ii)$ $2Cu + O_2 \rightarrow 2CuO$
In this reaction, $Cu$ gains oxygen to form $CuO$, therefore $Cu$ is oxidized.

(N/A) $X$ is copper $(Cu)$ and the black-coloured compound formed is copper oxide $(CuO)$.
The chemical reaction that occurs when copper is heated in air is as follows:
$2Cu (s) + O_2 (g) \xrightarrow{\text{Heat}} 2CuO (s)$
In this reaction,copper reacts with oxygen to form copper$(II)$ oxide,which is black in colour.

(B) Iron articles are painted to prevent them from rusting.
Rusting is a chemical process that occurs when iron is exposed to moisture and oxygen in the air.
Applying a layer of paint creates a physical barrier that cuts off the contact between the iron surface and the atmospheric moisture and oxygen.
Since the presence of both moisture and oxygen is essential for the rusting process,painting effectively prevents the corrosion of iron.

(A) Nitrogen is an inert gas and does not easily react with these substances.
On the other hand,oxygen reacts with food substances and makes them rancid.
Thus,bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack.
When oxygen is not present inside the pack,rancidity of oil and fat containing food items is avoided.

(N/A) Corrosion:
Corrosion is defined as a process where materials,usually metals,deteriorate as a result of a chemical reaction with their environment,such as air,moisture,or chemicals.
For example,iron,in the presence of moisture,reacts with oxygen to form hydrated iron oxide.
$4Fe + 3O_2 + nH_2O \to 2Fe_2O_3 \cdot nH_2O$ (Hydrated iron oxide)
This hydrated iron oxide is commonly known as rust.

(N/A) Rancidity:
The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.
For example,the taste and smell of butter changes when kept for a long time.
Rancidity can be prevented by:
$1.$ Storing food in airtight containers.
$2.$ Storing food in refrigerators.
$3.$ Adding antioxidants.
$4.$ Storing food in an environment of nitrogen gas.

(N/A) Reduction is defined as the loss of oxygen from a substance during a chemical reaction.
For example:
$(i)$ $\mathop {CO_2 + H_2 \to CO}\limits_{\text{Removal of oxygen - reduction}} + H_2O$
$(ii)$ $\mathop {CuO + H_2 \xrightarrow{\Delta } Cu}\limits_{\text{Loss of oxygen - reduction}} + H_2O$
In equation $(i)$, $CO_2$ is reduced to $CO$ due to the loss of oxygen, and in equation $(ii)$, $CuO$ is reduced to $Cu$ due to the loss of oxygen.