# Chemical Reactions : Complete Set of Questions This set of questions contains all the possible concepts
which could be asked in the examination

Introduction to Chemical Equation

Q.1 What is meant by a chemical reaction?

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.

Example rusting of iron, burning of coal and digestion of food etc.

Q.2 Is burning of a candle wax a physical change or a chemical change?

Chemical change(candle wax is a hydrocarbon,which burns to produce co2, soot etc.)

Q.3 State one difference between a physical change and a chemical change?

In a physical change, no new substance is formed while in a chemical change, a new substance is formed.

Q.4 A magnesium ribbon should be cleaned before burning it in air. Why?

It should be cleaned to remove the dust particles and its oxides that may be present on  its upper surface, so that it comes directly in contact with air.

Q.5 What do you mean by balanced chemical reaction?

The equations in which atoms of various elements on the reactants and the products side are equal.

Eg: - $Zn + {H_2}S{O_4} \to ZnS{O_4} + {H_2}$

In this equation the number of atoms of Zn,H,S  and O are equal on both sides, this means equation is balanced.

Q.6 Which one is a chemical change—rusting of iron or melting of iron?

Rusting of iron.

Q.7 What does symbol (aq) represent in a chemical equation?

The symbol (aq) represents aqueous solution. When it is written after a chemical formula in a chemical equation, it represents that the element or compound is a aqueous solution i.e water is added into the solution.

Q.8 Complete and balance the following equations :

(a) $NaOH + ....... \to N{a_2}S{O_4} + {H_2}O$

(b) $Ca{(OH)_2} + ......... \to CaC{O_3} + {H_2}O$

(a) $2NaOH + {H_2}S{O_4} \to N{a_2}S{O_4} +2 {H_2}O$

(b) $Ca{(OH)_2} + C{O_2} \to CaC{O_3} + {H_2}O$

Q.9 Correct and balance the following equation :

(a) $Ca + {H_2}O \to CaOH + H$

(b) $N + H \to N{H_3}$

The corrected and balanced equations are as follows :

(a) $Ca + 2{H_2}O \to Ca{\left( {OH} \right)_2} + {H_2}$

(b) ${N_2} + 3{H_2} \to 2N{H_3}$

Q.10 Fill in the following blanks with suitable words : -

(a) Chemical equations are balanced to satisfy the law of __________.

(b) A solution made in water is known as an ___________ solution and indicated by the symbol _________.

(a) Conservation of mass

(b) Aqueous, (aq)

Q.11 Write the balance of chemical equation for the following reaction.

Zinc + Silver Nitrate $\to$ Zinc nitrate + Silver ?

The balanced chemical equation is as follows : -

$Zn\left( s \right) + 2AgN{O_3}\left( {aq} \right) \to Zn{\left( {N{O_3}} \right)_2}\left( {aq} \right) + 2Ag\left( s \right)$

Q.12 Write the essential condition for following reaction to take place.

$2AgCl \to 2Ag + C{l_2}$ and write one use of this reaction.

To carry out the reaction, presence of sunlight is essential.

This reaction is used in black and white photography.

Q.13 List any four observations that help us to determine whether a chemical reaction has taken place ?

(i) Change in state

(ii) Change in colour

(iii) Evolution of a gas

(iv) Change in temperature.

Q.14 On what basis is a chemical equation balanced?

A chemical equation is balanced on the basis of law of conservation of mass. According to this law mass can neither be created nor be destroyed.

Q.15 Why is respiration considered an exothermic process?

In respiration process, glucose undergoes slow combustion reaction , it combines with oxygen to form carbon-dioxide, water and energy. The reaction in which energy is released is called as exothermic reaction, hence respiration is a exothermic process.

${C_6}{H_{12}}{O_6}\left( {aq} \right) + 6{O_2}\left( g \right) \to 6C{O_2}\left( g \right) + 6{H_2}O\left( l \right) + Energy$

Q.16 What happens chemically when quicklime is added to water filled in a bucket?

Quicklime is chemically a calcium oxide, when it added to water filled in a bucket, it reacts with water chemically and form slaked lime as a product and produce heat energy. So, water filled in the bucket becomes hot. Q.17 Why is photosynthesis considered an endothermic reaction?

In the photosynthesis  process light energy from sunlight is absorbed to produce oxygen and glucose from carbon-dioxide and water in the presence of chlorophyll, and the process in which energy is absorbed is called as endothermic reaction, hence photosynthesis is a endothermic reaction.

Q.18 How will you indicate the following effects in a chemical equation?

(a) A solution made in water

(b) Exothermic reaction

(c) Endothermic reaction

(a) A solution made in water is represented by writing (aq) after its formula in a chemical equation (b) Exothermic reaction is represented by writing ‘heat’ or ‘energy’ on the products side of a chemical reaction. (c) Endothermic reaction is indicated by writing ‘heat’ or ‘energy’ on the reactants side of a chemical reaction. Q.19 Write complete balanced equations for the following reactions:

(a) Calcium(solid)+water(liquid)  →  Calcium hydroxide(solution)+Hydrogen(gas)

(b) Sulphur dioxide(gas)+oxygen(gas) → Sulphur trioxide(gas)

(a) $Ca\left( s \right) + 2{H_2}O\left( l \right) \to Ca{\left( {OH} \right)_2}\left( {aq} \right) + {H_2}\left( g \right)$

(b) $2S{O_2}\left( g \right) + {O_2}\left( g \right) \to 2S{O_3}\left( g \right)$

Q.20 Write the rules for writing a word equation for a chemical reaction. Give one example ?

(a) The reactants are written on the left hand slide with the plus sign (+) in between them.

(b) The products are written on the right hand side with a plus sign between them.

(c) An arrowhead pointed towards the products is marked between the reactant and the products.

E.g. : - Magnesium + Oxygen – Magnesium oxide.

Q.21 Balance the following chemical reactions : -

(a) $Mn{O_2} + HCl \to MnC{l_2} + C{l_2} + {H_2}O$

(b) $Fe\left( s \right) + {H_2}O\left( g \right) \to F{e_3}{O_4}\left( s \right) + {H_2}\left( g \right)$

(c) $BaC{l_2}\left( {aq} \right) + A{l_2}{\left( {S{O_4}} \right)_3}\left( {aq} \right) \to BaS{O_4}\left( s \right) + AlC{l_3}\left( {aq} \right)$

(a) $Mn{O_2} + 4HCl \to MnC{l_2} + C{l_2} + 2{H_2}O$

(b) $3Fe\left( s \right) + 4{H_2}O\left( g \right) \to F{e_3}{O_4}\left( s \right) + 4{H_2}\left( g \right)$

(c) $3BaC{l_2}\left( {aq} \right) + A{l_2}{\left( {S{O_4}} \right)_3}\left( {aq} \right) \to 3BaS{O_4}\left( s \right) + 2AlC{l_3}\left( {aq} \right)$

Q.22 (a) Give one example of a chemical reaction.

(b) State two characteristics of the chemical reaction which takes place when dilute sulphuric acid is poured over zinc granules.

(c) Give two characteristics of the chemical reaction occurs on adding potassium iodide solution to lead nitrate solution ?

(a) Example of a chemical reaction : -

Respiration is an exothermic chemical reaction.

${C_6}{H_{12}}{O_6}\left( {aq} \right) + C{O_2}\left( {aq} \right) \to 6C{O_2} + 6{H_2}O + Energy$

(b) When dilute sulphuric acid is poured over Zinc granules : -

(i) Hydrogen gas is evolved.

(ii) Mixture becomes hot.

Reaction : $Zn + {H_2}S{O_4} \to ZnS{O_4} + {H_2} + Heat$

(c) On adding potassium iodide solution to lead nitrate solution : -

(i) Yellow precipitate of lead iodide are formed.

(ii) Colour of the solution changes from colourless to yellow.

$2KI + Pb{\left( {N{O_3}} \right)_2} \to Pb{I_2} + 2KN{O_3}$

Q.23 (a) What is a chemical equation ? Explain with the help of an example ?

(b) Giving examples, state the difference between balanced and unbalanced chemical equations.

(c) Balance the following chemical equation : -

(i) $N{H_3} \to {N_2} + {H_2}$

(ii) $C + C{O_2} \to CO$

(a) The method of representing a chemical reaction with the help of symbols and formulae of the substances involved in it is known as chemical equation.

For e.g. : - Burning of magnesium ribbon in air to give white powder of magnesium oxide. (b) (c)

(i) $2N{H_3} \to {N_2} + 3{H_2}$

(ii) $C + C{O_2} \to 2CO$

Q.24 What happens when silver chloride is exposed to sunlight ? write a chemical equation for this reaction. Also give one use of such a reaction ?

When silver chloride is exposed to sunlight, decomposition of silver chloride takes place.

- The chemical reaction is given as :

$2AgCl\left( s \right) \to 2Ag\left( s \right) + C{l_2}$

Use : -

This reaction is used in black and white photography

Q.25 Balance the following chemical reactions : -

(a) $Al + CuC{l_2} \to 2AlC{l_3} + 3Cu$

(b) $PbO + HCl \to PbC{l_2} + {H_2}O$

(c) $N{H_3} + {O_2} \to NO + {H_2}O$

(a) $2Al + 3CuC{l_2} \to 2AlC{l_3} + 3Cu$

(b) $PbO + 2HCl \to PbC{l_2} + {H_2}O$

(c) $4N{H_3} + 5{O_2} \to 4NO + 6{H_2}O$

Q.26 What is meant by a skeletal chemical equation ? What does it represent ? Using the equation for electrolytic decomposition of water, differentiate between a skeletal chemical equation and a balanced chemical equation ?

Skeletal chemical equation is an unbalanced chemical equation.

It represents a chemical reaction. Q.27 Write balanced chemical equations for the following reactions : -

(a) Sodium carbonate on reaction with hydrochloric acid in equimolar concentrations gives sodium chloride and sodium hydrogen carbonate.

(b) Calcium carbonate on reaction with hydrochloric acid gives calcium chloride, water and carbon dioxide.

(c) Nitrogen reacts with hydrogen under pressure to form ammonia. Q.28 Write the balanced chemical equation for the following reactions.

(a) Sodium carbonate solution on reaction with hydrochloric acid in equinolar cancentration gives sodium chloride and sodium hydrogen carbonate.

(b) When cold water is added to sodium violent exothermic reaction takes place and sodium hydroxide and hydrogen are produced.

(c) Potassium metal reacts with water to give potassium hydroxide and hydeogin is released.

(a) $N{a_2}C{O_3}\left( {aq} \right) + HCl\left( {aq} \right) \to NaCl\left( {aq} \right) + NaHC{O_3}\left( {aq} \right)$

(b) $2Na\left( s \right) + 2{H_2}O\left( l \right) \to 2NaOH\left( {aq} \right) + {H_2} + Heat$

(c) $2K\left( s \right) + 2{H_2}O\left( l \right) \to 2KOH\left( {aq} \right) + {H_2}$

Q.29 (a) What is meant by a chemical reaction ? Explain with the help of an example ?

(b) Give one example each of a chemical reaction characterised by :

(i) evolution of a gas

(ii) change in colour

(iii) formation of a precipitate

(iv) change in temperature

(v) change in state ?

(a) Chemical reaction is the process in which new substances with new properties are formed. During a chemical reaction, atoms of one element do not change into those of another element only a rearrangement of atoms takes place in a chemical reaction.
eg : - The burning of magnesium in air to form magnesium oxide is an example of a chemical reaction. (b) (i) Evolution of a gas : When zinc granules react with dilute sulphuric acid in a flask, hydrogen gas evolves. (ii) Change in colour : The chemical reaction between sulphur dioxide gas and acidified potassium dichromate solution is characterised by a change in colour from orange to green.

(iii) Formation of a precipitate : The chemical reaction between potassium iodide and lead nitrate is characterised by the formation of a yellow precipitate of lead iodide.

(iv) Change in temperature : - The chemical reaction between quicklime and water to form slaked lime is characterised by change in temperature. (v) Change in state : The combustion reaction of candle wax is characterised by change in state from solid to liquid and gas.

Q.30 (a) What do you understand by exothermic and endothermic reactions.

(b) Give one example of an exothermic reaction and endothermic reaction.

(c) Find out endothermic & exothermic reactions from the following ?

(i) Respiration

(ii) Photosynthesis

(iii) Burning of natural gas

(iv) Digestion of food

(a) Exothermic reactions: Those reactions in which heat is evolved are known as exothermic reactions.

Endothermic reactions: Those reactions in which heat is absorbed are known as endothermic reactions.

(b) Example of exothermic reaction : When natural gas burns in the oxygen of air, it forms CO2 and water vapour and large amount of heat is evolved.

$C{H_4} + 2{O_2} \to C{O_2} + 2{H_2}O + Heat$

Example of endothermic reaction : When nitrogen and oxygen are heated to a very high temperature, they combine to form nitrogen monoxide.

${N_2} + {O_2} + Heat \to 2NO$

(c) Exothermic reactions : -

(i) Respiration

(ii) Burning of natural gas

(iii) Digestion of food

Endothermic reactions

(iv) Photosynthesis

Q.31 (a) What happens when an  aqueous solution of sodium of sodium sulphate reacts with an aqueous solution of barium chloride ?

(b) Write the balanced chemical equation for the reaction which takes place.

(c) State the physical conditions of reactants in which the reaction will not take place.

(d) Name the type of chemical reaction which occurs ?

(a) When an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride, exchange of ions between both the reactants takes place and precipitate of barium sulphate forms. It is a precipitation reaction

(b) The balanced chemical reaction, which takes place is as : -

$N{a_2}S{O_4} + BaC{l_2} \to BaS{O_4} + 2NaCl$

(c) Reaction will not takes place . If physical state of reactants are solid state

(d) Double displacement reaction takes place

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