Types of Chemical Reactions Questions in English

(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.

(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.

(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) 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) 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) Zinc is more reactive than iron. Therefore,when zinc is added to a solution of iron $(II)$ sulphate,it displaces iron from the solution,resulting in the formation of zinc sulphate and iron metal.
The chemical reaction is:
$Zn_{(s)} + FeSO_{4(aq)} \to ZnSO_{4(aq)} + Fe_{(s)}$

(C) double displacement reaction is a chemical reaction where two reactant compounds exchange ions to form two new compounds.
$(i)$ $Pb + CuCl_{2} \rightarrow PbCl_{2} + Cu$ is a displacement reaction where $Pb$ displaces $Cu$.
$(ii)$ $Na_{2}SO_{4} + BaCl_{2} \rightarrow BaSO_{4} + 2NaCl$ is a double displacement reaction where $Na^+$ and $Ba^{2+}$ ions exchange places.
$(iii)$ $C + O_{2} \rightarrow CO_{2}$ is a combination reaction.
$(iv)$ $CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O$ is a combustion reaction.
Therefore,only $(ii)$ is a double displacement reaction.

(B) The chemical equation for the reaction is:
$BaCl_2(aq) + (NH_4)_2SO_4(aq) \rightarrow BaSO_4(s) + 2NH_4Cl(aq)$
$1$. In this reaction, the ions $Ba^{2+}$ and $NH_4^+$ are exchanged between the reactants, which characterizes a $\text{Double displacement reaction}$ $(iv)$.
$2$. Barium sulphate $(BaSO_4)$ is formed as an insoluble white solid, which is known as a precipitate. Therefore, this is also a $\text{Precipitation reaction}$ $(ii)$.
Thus, both $(ii)$ and $(iv)$ are correct.

(C) The chemical equation for the electrolysis of water is: $2H_2O(l) \rightarrow 2H_2(g) + O_2(g)$.
According to the balanced chemical equation,$2$ moles of water decompose to produce $2$ moles of hydrogen gas and $1$ mole of oxygen gas.
Therefore,the mole ratio of hydrogen gas to oxygen gas liberated is $2:1$.

(A) double displacement reaction requires soluble ionic compounds to provide ions in the solution.
Lead nitrate is soluble in water and provides $Pb^{2+}$ ions,which react with $I^-$ ions from potassium iodide to form a yellow precipitate of lead iodide $(PbI_2)$.
Lead acetate is also a soluble lead salt that dissociates to provide $Pb^{2+}$ ions,making it a suitable substitute for lead nitrate in this reaction.
Lead sulphate is insoluble in water and will not provide the necessary $Pb^{2+}$ ions for the reaction to occur.

(C) $1$. The given reaction is $2KClO_{3(s)} \xrightarrow[Catalyst]{Heat} 2KCl_{(s)} + 3O_{2(g)}$.
$2$. In this reaction,a single reactant $(KClO_3)$ breaks down into simpler products ($KCl$ and $O_2$),which characterizes it as a decomposition reaction.
$3$. The reaction requires the supply of heat (thermal energy) to proceed,which indicates that it is an endothermic reaction.
$4$. Therefore,the correct statement is that it is a decomposition reaction and endothermic in nature.

(D) chemical reaction involves the formation of new substances with different chemical properties.
$A$. Storing oxygen gas under pressure is a physical change as it only changes the state of the gas.
$B$. Liquefaction of air is a physical process involving changes in temperature and pressure.
$C$. Keeping petrol in an open dish is a physical process of evaporation.
$D$. Heating copper wire in the presence of air at high temperature leads to the formation of copper$(II)$ oxide $(2Cu + O_2 \rightarrow 2CuO)$. This is a chemical reaction because a new substance is formed.

(B) combination reaction is a reaction in which two or more reactants combine to form a single product.
$(i) 2 KClO_3 \xrightarrow{\text{Heat}} 2 KCl + 3 O_2$: This is a decomposition reaction because a single reactant breaks down into simpler products.
$(ii) MgO + H_2O \longrightarrow Mg(OH)_2$: This is a combination reaction because two reactants ($MgO$ and $H_2O$) combine to form a single product $(Mg(OH)_2)$.
$(iii) 4 Al + 3 O_2 \longrightarrow 2 Al_2O_3$: This is a combination reaction because two reactants ($Al$ and $O_2$) combine to form a single product $(Al_2O_3)$.
$(iv) Zn + FeSO_4 \longrightarrow ZnSO_4 + Fe$: This is a displacement reaction because $Zn$ displaces $Fe$ from its salt solution.
Therefore, $(ii)$ and $(iii)$ are combination reactions.

(N/A) The chemical reaction between potassium chloride $(KCl)$ and silver nitrate $(AgNO_3)$ is as follows:
$KCl(aq) + AgNO_3(aq) \longrightarrow AgCl(s) + KNO_3(aq)$
In this reaction,silver chloride $(AgCl)$ is formed as an insoluble white precipitate.
This is a double displacement reaction because there is an exchange of ions between the reactants.
It is also classified as a precipitation reaction because an insoluble solid (precipitate) is formed.

(N/A) The chemical reaction for the thermal decomposition of ferrous sulphate is:
$2FeSO_4(s) \xrightarrow{\text{Heat}} Fe_2O_3(s) + SO_2(g) + SO_3(g)$
In this reaction,green ferrous sulphate crystals lose water on heating and then decompose to form ferric oxide,sulphur dioxide,and sulphur trioxide. The gas evolved $(SO_2)$ has the characteristic smell of burning sulphur. Since a single reactant breaks down into multiple products upon heating,it is classified as a thermal decomposition reaction.

(N/A) Silver chloride $(AgCl)$ is a light-sensitive compound.
When exposed to sunlight,it undergoes a photochemical decomposition reaction to form metallic silver and chlorine gas.
The chemical equation for this reaction is:
$2AgCl(s) \xrightarrow{\text{sunlight}} 2Ag(s) + Cl_2(g)$
To prevent this decomposition and preserve the chemical,it is stored in dark-coloured bottles that block light.

(N/A) Balanced chemical equation:
$2Cu(NO_3)_2(s) \xrightarrow{\text{Heat}} 2CuO(s) + O_2(g) + 4NO_2(g)$
$(b)$ The brown gas $X$ evolved is nitrogen dioxide $(NO_2)$.

(B) When a strip of copper metal is placed in a silver nitrate solution,a displacement reaction occurs because copper is more reactive than silver.
Metallic silver is precipitated as a solid,and the solution turns blue due to the formation of copper$(II)$ nitrate.
The chemical equation is: $Cu(s) + 2AgNO_3(aq) \to 2Ag(s) + Cu(NO_3)_2(aq)$.

(A) chemical change involves the formation of new substances with different chemical properties.
Fermentation of fruit juice is a chemical change because microorganisms (like yeast) convert sugars into alcohol and carbon dioxide,resulting in a new substance.
Diluting fruit juice is a physical change because it only involves adding water to the juice,which does not change the chemical composition of the juice components.

(N/A) During the electrolysis of water,the water molecule $(H_{2}O)$ decomposes into hydrogen gas $(H_{2})$ and oxygen gas $(O_{2})$ in a specific molar ratio.
The chemical equation for this process is:
$2H_{2}O(l) \xrightarrow{\text{Electrolysis}} 2H_{2}(g) + O_{2}(g)$
According to the balanced chemical equation,for every $2$ moles of water decomposed,$2$ moles of hydrogen gas are produced at the cathode and $1$ mole of oxygen gas is produced at the anode.
Therefore,the volume of hydrogen gas collected is double the volume of oxygen gas collected,resulting in a ratio of $2:1$.

(A) Electrolysis of water is a chemical change because it involves the decomposition of water $(H_2O)$ into hydrogen $(H_2)$ and oxygen $(O_2)$ gases using electricity,resulting in the formation of new substances.
Sodium chloride $(NaCl)$ is stable under sunlight and does not undergo a chemical change when exposed to it.

(N/A) The green iron salt is Ferrous sulphate heptahydrate $(FeSO_{4} \cdot 7H_{2}O)$. Upon strong heating, it loses water of crystallization and then decomposes into Ferric oxide $(Fe_{2}O_{3})$, which is black in colour, along with sulphur dioxide $(SO_{2})$ and sulphur trioxide $(SO_{3})$ gases.
$(b)$ This is a thermal decomposition reaction because a single reactant breaks down into multiple products upon the application of heat.

(N/A) Digestion of food involves the breakdown of complex food molecules into simpler substances,which is a decomposition reaction.
$(b)$ Combustion of coal involves the reaction of carbon with oxygen to form carbon dioxide,which is a combination reaction.

(A) Combination reaction: In this reaction,two or more reactants combine to form a single product $(2H_2 + O_2 \rightarrow 2H_2O)$.
$(b)$ Decomposition reaction: In this reaction,a single reactant breaks down into two or more simpler products under the influence of electricity $(2H_2O \xrightarrow{\text{electricity}} 2H_2 + O_2)$.

(N/A) $(i)$ In the manufacturing of cement,quicklime $(CaO)$ is used,which is obtained by the thermal decomposition of limestone $(CaCO_3)$:
$CaCO_3(s) \xrightarrow{\text{Heat}} CaO(s) + CO_2(g)$
$(ii)$ In the manufacturing of photochromic glass,silver chloride $(AgCl)$ or silver bromide $(AgBr)$ is used,which undergoes photochemical decomposition in sunlight to form metallic silver,causing the glass to darken:
$2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$
$2AgBr(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Br_2(g)$

(N/A) $(i)$ The essential condition for the reaction $2 AgCl \rightarrow 2 Ag + Cl_{2}$ to occur is the presence of sunlight (photolytic decomposition).
$(ii)$ This reaction is used in black and white photography.

(A) The thermal decomposition of ferrous sulfate $(FeSO_{4})$ is a classic chemical reaction.
When heated,ferrous sulfate crystals lose water and then decompose to form ferric oxide $(Fe_{2}O_{3})$,sulfur dioxide $(SO_{2})$,and sulfur trioxide $(SO_{3})$.
The balanced chemical equation is:
$2 FeSO_{4} \xrightarrow{\text{Heat}} Fe_{2}O_{3} + SO_{2} + SO_{3}$

(N/A) $(i)$ The colour of the precipitate formed is yellow.
$(ii)$ The compound precipitated is lead iodide,which has the chemical formula $PbI_{2}$.

(N/A) $(i)$ The balanced chemical equation is:
$2KI(aq) + Pb(NO_3)_2(aq) \to PbI_2(s) \downarrow + 2KNO_3(aq)$
$(ii)$ This is a double displacement reaction. Since an insoluble solid (precipitate) is formed,it is also classified as a precipitation reaction.

(N/A) $KCl(aq) + AgNO_3(aq) \to AgCl(s) \downarrow + KNO_3(aq)$
In this reaction, potassium chloride reacts with silver nitrate to form silver chloride, which is an insoluble white precipitate, and potassium nitrate.

(A-D) The chemical reaction is: $KCl(aq) + AgNO_3(aq) \rightarrow AgCl(s) + KNO_3(aq)$.
$(a)$ Double displacement reaction: The ions $K^+$ and $Ag^+$ exchange their partners to form new products.
$(b)$ Precipitation reaction: An insoluble white solid, silver chloride $(AgCl)$, is formed as a precipitate.

(N/A) chemical reaction involving a change in colour can be observed when lead nitrate solution reacts with potassium iodide solution. The reaction mixture changes from colourless to a yellow precipitate.
The balanced chemical equation is:
$Pb(NO_3)_2(aq) + 2KI(aq) \rightarrow PbI_2(s) + 2KNO_3(aq)$
In this reaction,lead$(II)$ iodide $(PbI_2)$ is formed as a yellow precipitate.

(N/A) change in temperature occurs during an exothermic reaction, where heat is released into the surroundings.
Example: The reaction between zinc granules and dilute sulphuric acid.
Chemical equation: $Zn(s) + H_2SO_4(aq) \rightarrow ZnSO_4(aq) + H_2(g) + \text{Heat}$

(N/A) Formation of a precipitate occurs when two aqueous solutions react to form an insoluble solid product,known as a precipitate.
Example: The reaction between barium chloride and sodium sulphate results in the formation of a white precipitate of barium sulphate.
Chemical equation:
$BaCl_{2}(aq) + Na_{2}SO_{4}(aq) \rightarrow BaSO_{4}(s) + 2NaCl(aq)$

(N/A) $(i)$ Electricity (Electrolytic decomposition):
$2H_{2}O(l) \xrightarrow{\text{Electric current}} 2H_{2}(g) + O_{2}(g)$
$(ii)$ Heat (Thermal decomposition):
$CaCO_{3}(s) \xrightarrow{\text{Heat}} CaO(s) + CO_{2}(g)$
$(iii)$ Sunlight (Photolytic decomposition):
$2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_{2}(g)$

(N/A) $(i)$ $(a)$ At the anode,oxygen gas is evolved.
$(b)$ At the cathode,hydrogen gas is evolved.
$(ii)$ The amounts of gases collected in the two test tubes are not of the same volume because water $(H_2O)$ consists of hydrogen and oxygen in a molar ratio of $2:1$. Thus,twice as much hydrogen gas is produced compared to oxygen gas.
$(iii)$ This reaction is an electrolytic decomposition reaction.
$(iv)$ Pure water is a poor conductor of electricity. Salt water is used to act as an electrolyte,allowing electricity to pass through the solution to facilitate the decomposition of water.

(N/A) This is a combination reaction. It is defined as a reaction in which a single product is formed from two or more reactants.
$(b)$ The balanced chemical equation is: $CaO(s) + H_2O(l) \rightarrow Ca(OH)_2(aq)$. The chemical name of the product obtained is calcium hydroxide.
$(c)$ Two observations made during the reaction are:
$(i)$ The reaction occurs vigorously with the evolution of heat (exothermic reaction).
$(ii)$ The beaker becomes hot to the touch due to the release of thermal energy.

(N/A) $(i)$ Take $2 \, g$ of silver chloride in a china dish.
(ii) Place this china dish in sunlight for some time.
(iii) Observe the colour of silver chloride after some time. Silver chloride turns grey in sunlight due to the decomposition of $AgCl$ into $Ag$ and $Cl_2$.
Chemical equation:
$2AgCl(s) \xrightarrow{\text{Sunlight}} 2Ag(s) + Cl_2(g)$
Use: This reaction is used in black and white photography.

(N/A) $(i)$ Before heating: Pale green. After heating: Brown or reddish-brown.
$(ii)$ The gases produced are sulphur dioxide $(SO_{2})$ and sulphur trioxide $(SO_{3})$.
$(iii)$ The chemical equation for the thermal decomposition of ferrous sulphate is:
$2FeSO_{4}(s) \xrightarrow{\text{Heat}} Fe_{2}O_{3}(s) + SO_{2}(g) + SO_{3}(g)$

(N/A) $(i)$ Dazzling white light is emitted during the burning of magnesium.
$(ii)$ $A$ white powdery substance (magnesium oxide) is formed after the burning process.

(N/A) $(i)$ This is a displacement reaction because zinc $(Zn)$ displaces hydrogen $(H_{2})$ from sulfuric acid $(H_{2}SO_{4})$.
$(ii)$ This is a combination reaction because calcium oxide $(CaO)$ and water $(H_{2}O)$ combine to form a single product,calcium hydroxide $(Ca(OH)_{2})$.

(N/A) $(i)$ This is a decomposition reaction because a single reactant breaks down into two or more simpler products upon heating.
$(ii)$ This is a double displacement reaction because there is an exchange of ions between the two reactants to form new compounds.

(N/A) The chemical reaction is: $Zn(s) + H_2SO_4(aq) \longrightarrow ZnSO_4(aq) + H_2(g) \uparrow$
Observations:
$(i)$ Evolution of hydrogen gas bubbles is observed.
$(ii)$ The reaction is exothermic,so the temperature of the reaction vessel increases.

(N/A) The chemical reaction is: $2KI(aq) + Pb(NO_3)_2(aq) \to PbI_2(s) \downarrow + 2KNO_3(aq)$
$(i)$ $A$ yellow precipitate of lead iodide $(PbI_2)$ is formed.
$(ii)$ The reaction is a double displacement reaction where the solution changes appearance due to the formation of an insoluble solid.

(N/A) The chemical equation for the thermal decomposition of lead nitrate is:
$2Pb(NO_{3})_{2}(s) \xrightarrow{\Delta} 2PbO(s) + 4NO_{2}(g) + O_{2}(g)$
Observations:
$(i)$ Evolution of reddish-brown fumes of nitrogen dioxide $(NO_{2})$ gas.
$(ii)$ Formation of a yellow-colored residue of lead$(II)$ oxide $(PbO)$ in the test tube.

(N/A) Applications of a decomposition reaction:
$(a)$ White silver chloride turns grey in sunlight due to the decomposition of silver chloride into silver and chlorine.
$2 AgCl (s) \xrightarrow{\text{sunlight}} 2 Ag (s) + Cl_2 (g)$
This reaction is used in black and white photography.
$(b)$ Potassium chlorate $(KClO_3)$ decomposes on heating to produce oxygen gas.
$2 KClO_3 (s) \xrightarrow{\text{heat}} 2 KCl (s) + 3 O_2 (g)$
This is a common laboratory method for the preparation of oxygen gas.
$(c)$ Quicklime $(CaO)$ is prepared by the thermal decomposition of calcium carbonate ($CaCO_3$,limestone).
$CaCO_3 (s) \xrightarrow{\text{heat}} CaO (s) + CO_2 (g)$
Quicklime is used in the manufacture of cement and for preparing slaked lime used in whitewashing.

(N/A) Observations:
$(a)$ The reaction occurs vigorously.
$(b)$ $A$ large amount of heat is released (exothermic reaction).
Uses of the product $Ca(OH)_2$ (Calcium hydroxide):
$(a)$ It is used for whitewashing walls. It reacts slowly with $CO_2$ in the air to form a thin layer of calcium carbonate $(CaCO_3)$ on the walls,providing a shiny finish.
$(b)$ It is used as a laboratory reagent for testing the presence of $CO_2$ gas,as it turns milky upon reaction with it.