Class 10 LAKHMIR SINGH AND MANJIT KAUR Solutions Chemistry Chapter 1 - Chemical Reactions and Equations

Respiration is an exothermic process because energy is produced during this process.

A balanced chemical equation has equal number of atoms of different elements in the reactants and products.

When quicklime is added to water, it forms slaked lime along with evolution of heat. There will be a rise in temperature of the bucket.

Magnesium ribbon should be cleaned before burning in air to remove the protective layer of basic magnesium carbonate from its surface.

False.

Oxygen should be in molecular form, O₂

2Mg + O₂ 2MgO

The symbol (aq) represents aqueous solution in a chemical equation.

Photosynthesis is an endothermic reaction because sunlight energy is absorbed by green plants during this process.

(a) Aqueous solution is indicated by the symbol 'aq'.

(b) An exothermic reaction is indicated by writing "+Heat" or "+Heat energy" or "+Energy" on the products side of an equation.

(c) An endothermic reaction is indicated by writing "+Heat" or "+Heat energy" or "+Energy" on the reactants side of an equation.

(a) 2H₂S + 3O₂ 2H₂O + 2SO₂

(b) P₄ + 5O₂ 2P₂O₅

(c) CS₂ + 3O₂ CO₂ + 2SO₂

(d) 2Al + Fe₂O₃ Al₂O₃ + 2Fe

(e) BaCl₂ + ZnSO₄ ZnCl₂ + BaSO₄

(a) Ca(OH)₂ + CO₂ CaCO₃ + H₂O

(b) 2Al + 3CuCl₂ 2AlCl₃ + 3Cu

(a) 2NaOH + H₂SO₄ Na₂SO₄ + 2H₂O

(b) Ca(OH)₂ + CO₂ CaCO₃ + H₂O

(i) Ca + 2H₂O Ca(OH)₂ + H₂

(ii) N₂ + 3H₂ 2NH₃

(a) Ca (s) + 2H₂O (l) Ca(OH)₂ (aq) + H₂ (g)

(b) 2SO₂ (g) + O₂ (g) 2SO₃ (g)

(i) 4Na + O₂ 2Na₂O

(ii) 2H₂O₂ 2H₂O + O₂

(iii) Mg(OH)₂ + 2HCl MgCl₂ + 2H₂O.

(iv) 4Fe + 3O₂ 2Fe₂O₃

(v) 2Al(OH)₃ Al₂O₃ + 3H₂O

(vi) 2NH₃ + 3CuO 3Cu + N₂ + 3H₂O

(vii) Al₂(SO₄)₃ + 6NaOH 2Al(OH)₃ + 3Na₂SO₄

(viii) 2HNO₃ + Ca(OH)₂ Ca(NO₃)₂ + 2H₂O

(ix) 2NaOH + H₂SO₄ Na₂SO₄ + 2H₂O

(x) BaCl₂ + H₂SO₄ BaSO₄ + 2HCl

(a) Conservation of mass

(b) Aqueous; (aq)

(a) Magnesium Ribbon is heated in the presence of air to form a white powder called magnesium oxide.

(b) When dilute sulphuric acid is poured over zinc granules (i) there will be a rise in temperature (ii) evolution of hydrogen gas.

(c) (i) A yellow precipitate is formed.

     (ii) There will be a change in color (from colourless to yellow).

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

Example: Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. This equation is written as: Zn + H₂SO₄ZnSO₄ + H₂

(b) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products.

Example: Zn + H₂SO₄ZnSO₄ + H₂

An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. It has unequal masses of various elements in the reactants and products.

Example: H₂ + O₂H₂O

(c) (i) 2NH₃ N₂ + 3H₂ (ii) C + CO₂ 2CO

H₂ + CuO Cu + H₂O

(i) Elements : H₂ and Cu

(ii) Compounds : CuO and H₂O

(iii) Reactants: H₂ and CuO

(iv) Products: Cu and H₂O

(v) Metal: Cu

(vi) Non-metal: H₂

(a) The various ways in which a chemical equation can be made more informative are :

(i) By indicating the physical states of the reactants and products. Example: Gaseous state is indicated by the symbol (g).

Zn (s) + H₂SO₄ (aq) ZnSO₄ (aq) + H₂ (g)

(ii) By indicating the heat changes taking place in the reaction. For xxample: An exothermic reaction is indicated by writing "+Heat" or "+Heat energy" or "+Energy" on the products side of an equation.

C (s) + O₂ (g) CO₂ (g) + Heat

(iii) By indicating the "conditions" under which the reaction takes place.

Example: Delta stands for heat which is written over the arrow of the equation.

(b) Ca(OH)₂ (aq) + CO₂ (g) CaCO₃ (s) + H₂O (l)

(a) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products. A chemical equation should be balanced to satisfy the law of conservation of chemical reactions.

(b) 2Al + 3Cl₂ 2AlCl₃

(c) 2K + 2H₂O 2KOH + H₂

(a) The physical states of the reactants and products are shown by putting the "state symbols" in an equation.

For example: Zn (s) + H₂SO₄ (aq)ZnSO₄ (aq) + H₂ (g)

(b) Zn (s) + 2HCl (aq) ZnCl₂ (aq) + H₂ (g)

(c) FeSO₄(aq) + 2NaOH (aq) Fe(OH)₂ (s) + Na₂SO₄ (aq)

(i) Evolution of gas.

For example: When sodium carbonate reacts with dilute hydrochloric acid, carbon dioxide gas is evolved.

(ii) Formation of a precipitate.

For example: When potassium iodide solution is added to a solution of lead nitrate, yellow precipitate of lead iodide is formed.

(a) 2Al(OH)₃ + 3H₂SO₄ Al₂(SO₄)₃ + 6H₂O

(b) MnO₂ + 4HCl MnCl₂ + Cl₂ + 2H₂O

(a) MgCO₃ (s) + 2HCl (aq) MgCl₂ (aq) + CO₂ (g) + H₂O (l)

(b) 2NaOH (aq) + H₂SO₄ (aq) Na₂SO₄ (aq) + 2H₂O (l)

The conditions for this reaction to take place are: a pressure of 300 atmospheres (written as 300 atm), a temperature of 300^oC, and a catalyst which is a mixture of zinc oxide and chromium oxide (ZnO + CrO₃).

(a) 2KClO₃ (s) 2KCl (s) + 3O₂ (g)

(b) 2Mg + CO₂ 2MgO + C

(a) CaCO₃ + 2HCl CaCl₂ + H₂O + CO₂

(b) NaOH (aq) + HCl (aq) NaCl (aq) + H₂O (l)

4NH₃ (g) + 3O₂ (g) 2N₂ (g) + 6H₂O (l)

6CO₂ (g) + 6H₂O (l) C₆H₁₂O₆ (aq) + 6O₂ (g)

Carbon dioxide Water Glucose Oxygen

3BaCl₂ (aq) + Al₂(SO₄)₃ (aq) 3BaSO₄ (s) + 2AlCl₃ (aq)

2KNO₃ (s) 2KNO₂ (s) + O₂ (g)

(a) Chemical reactions are the processes in which new substances with new properties are formed.

For example: When magnesium ribbon is heated, it burns in air to form a white powder called magnesium oxide.

(b) (i) The chemical reaction between zinc and dilute sulphuric acid.

(ii) The chemical reaction between citric acid and purple coloured potassium permanganate solution is characterised by change in colour (from purple to colourless).

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

(iv) The reaction between quick lime and water to form slaked lime is characterised by a change in temperature.

(v) When wax is burned, then water and carbon dioxide are formed. Wax is a solid; water is a liquid whereas carbon dioxide is a gas.

(a) The various characteristics of chemical reactions are:

(i) Evolution of a gas (ii) Formation of a precipitate (iii) Change in colour (iv) Change in temperature (v) Change in state.

(b) (i) Evolution of carbon dioxide gas (ii) Change in colour from purple to colourless (iii) Formation of white precipitate of barium sulphate (iv) Change in temperature (v) Change in state from solid to liquid and gas.

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

 The reactions in which heat is absorbed are known as endothermic reactions.

(b) Example of exothermic reaction:

C (s) + O₂ (g) CO₂ + Heat

Example of endothermic reaction:

N₂ (g) + O₂ (g) + Heat 2NO (g)

(c) Endothermic reactions: Photosynthesis, Electrolysis of water, Decomposition of calcium carbonate.

Exothermic reactions: Burning of natural gas, Respiration.

(a) Lead nitrate.

(b) Lead iodide.

(c) Formation of a precipitate.

(d) Pb(NO₃)₂ (aq) + 2KI (aq) PbI₂ (s) + 2KNO₃ (aq)

(a) Calcium oxide, CaO.

(b) Calcium hydroxide, Ca(OH)₂

(c) Lime water.

(d) CaO + H₂O Ca(OH)₂

(e) Change in temperature.

(a) Zinc and Iron.

(b) Dilute hydrochloric acid and dilute sulphuric acid.

(c) Hydrogen.

(d) Lighter than air.

(e) Exothermic.

(f) Suppose metal X is zinc (Zn) and acid Y is dilute hydrochloric acid (HCl) ;

Zn (s) + 2HCl (aq) ZnCl₂ (aq) + H₂ (g)

(a) Calcium carbonate (limestone), CaCO₃

(b) Calcium oxide, CaO

(c) Carbon dioxide, CO₂

(d) Calcium hydroxide, Ca(OH)₂; Lime water.

(e) Calcium carbonate; Limestone and Marble.

(a) Magnesium, Mg.

(b) Magnesium oxide, MgO

(c) Oxygen (of air), O₂

(d) Magnesium hydroxide, Mg(OH)₂; Used as antacid to relieve indigestion

(e) 2Mg + O₂ 2MgO

(a) Copper, Cu.

(b) Copper sulphate, CuSO₄, Blue colour.

(c) Copper hydroxide, Cu(OH)₂

(d) CuSO₄ (aq) + 2NaOH (aq) Cu(OH)₂ (s) + Na₂S0₄ (aq)

(a) Sodium, Na.

(b) Sodium hydroxide solution (NaOH solution), Alkaline. (c) Hydrogen, H₂

(d) 2Na + 2H₂O 2NaOH + H₂

(e) Exothermic.

(a) X is carbon monoxide gas (CO); Y is hydrogen gas (H₂) ; Z is methanol (or Methyl alcohol) (CH₃OH)

  (CH₄0 = CH₃OH)

(b) Formation of Z:

The conditions for this reaction to take place are: a pressure of 300 atmospheres (written as 300 atm), a temperature of 300^oC, and a catalyst which is a mixture of zinc oxide and chromium oxide (ZnO + CrO₃).

(a) Potassium chlorate, KClO₃

(b) Potassium chloride, KCl

(c) Oxygen, O₂

(d) Manganese dioxide, MnO₂; It acts as a catalyst in the decomposition of potassium chlorate to form oxygen gas

 (e) Catalysts

(a) Carbon dioxide, CO₂

(b) Water, H₂O

(c) Sunlight.

(d) Chlorophyll; Green leaves of plants.

(e) Glucose, C₆H₁₂O₆

(f) Oxygen; Photosynthesis.

Decomposition reaction.

The various types of chemical reactions are:

(i) Combination reactions.

(ii) Decomposition reaction.

(iii) Displacement reaction.

(iv) Double displacement reaction.

(v) Oxidation and reduction reactions.

The colour of copper sulphate solution changes when iron nail is kept immersed in it due to the displacement reaction taking place between iron and copper leading to formation of iron sulphate.

Zn + 2AgNO₃  Zn(NO₃)₂ + 2Ag

Rancidity.

Anti-oxidants.

The digestion of food in the body is an example of decomposition reaction.

Anti-oxidant is a substance which prevents oxidation. They are added to fat and oil containing foods so that they do not get oxidized easily and hence do not turn rancid.

Food products containing fats and oils are packaged in nitrogen so that there is no oxygen to cause oxidation of food and make it rancid.

(a) When fused sodium chloride is decomposed by passing electricity, sodium metal is obtained.

(b) When lead nitrate is heated strongly, it breaks down to form lead monoxide, nitrogen dioxide and oxygen.

Decomposition reactions (carried out by electricity).

BHA (Butylated Hydroxy Anisole) and BHT (Butylated Hydroxy Toluene).

(a) Decomposition reaction where heat is supplied for energy:

(b) Decomposition reaction where light is supplied for energy:

(c) Decomposition reaction where electricity is supplied for energy:

2AgNO₃ (aq) + Cu (s) Cu(NO₃)₂ (aq) + 2Ag (s)

(i) Decomposition.

(ii) Combination.

(iii) Decomposition.

(iv) Decomposition.

(v) Combination.

(a) Combination.

(b) Decomposition.

(c) Decomposition.

(d) Decomposition.

(e) Combination.

(i) Displacement reaction.

(ii) Combination reaction.

(iii) Decomposition reaction.

(iv) Double displacement reaction.

(v) Displacement reaction.

(a) Displacement reaction.

(b) Combination reaction.

(a) Combination reaction.

(b) Displacement reaction.

(c) Displacement reaction.

(d) Decomposition reaction.

(e) Double displacement reaction.

(a) H₂O₂

(b) PbS

H₂S

Substance oxidised: H₂S

Substance reduced: SO₂

(a) Oxidation; reduction.

(b) Reduction; oxidation.

(c) Rancidity.

Oxidation Reaction: The addition of oxygen (or removal of hydrogen) to a substance is called oxidation.

(i) C (ii) ZnO

(a) The oxidation and reduction reactions occurring together are called a redox reaction. Example:

In this reaction, copper oxide is being reduced to copper whereas hydrogen is being oxidised to water.

(b) Magnesium is oxidised as addition of oxygen to magnesium takes place leading to formation of magnesium oxide.

(c) (i) HCl

     (ii) _MnO2

     (iii) MnO₂

     (iv) HCl

(a) Those reactions in which two or more substances combine to form a single substance is called a combination reaction.

(b) C (s) + O₂ (g) CO₂ + Heat

(c) N₂ (g) + O₂ (g) + Heat 2NO (g)

(a) C (s) + O₂ (g) CO₂ + Heat

(b) Oxidation reaction is an exothermic reaction.

(c)

In this reaction, copper oxide is being reduced to copper whereas hydrogen is being oxidised to water.

(a) The colour of ferrous sulphate is green. It changes to brown after heating.

(b) The product formed is ferric oxide. This is a decomposition reaction.

Those reactions in which a compound splits up into two or more simpler substances is called a decomposition reaction.

When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

Activity: When potassium chlorrate is heated in the presence of manganese dioxide catalyst, it decomposes to give potassium chloride and oxygen:

This decomposition takes place in the presence of heat and catalyst. In this decomposition reaction, a single compound, potassium chlorate, is splitting up into two simpler substances, potassium chloride and oxygen. This decomposition reaction is used for preparing oxygen gas in the laboratory.

ZnO + C Zn + CO

(i) Zinc oxide.

(ii) Carbon.

(a) 

(b)

(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.

Equation: CuSO₄ (aq) + Zn (s) ZnSO₄ + Cu

Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

Equation: AgNO₃ (aq) + NaCl (aq) AgCl (s)+ NaNO₃ (aq)

(b) Any reaction in which an insoluble solid (called precipitate) is formed that separates from the solution is called a precipitation reaction.

Example: The reaction between barium chloride and sodium sulphate solution to form a white barium sulphate precipitate (alongwith sodium chloride solution) is an example of a precipitation reaction.

(a) (i) H₂S + Cl₂ S + 2HCl

In this reaction, H₂S is changing into S. That is, Hydrogen is being removed from hydrogen sulphide. Now, by definition, the removal of hydrogen from a compound is called oxidation, so, we can say that hydrogen sulphide is being oxidised to sulphur. On the other hand, Cl₂ is changing into HCl. That is, hydrogen is being added to chlorine. By definition, the addition of hydrogen to a substance is called reduction, so we can say that chlorine is being reduced to hydrogen chloride.

(b) 2Mg + O₂ 2MgO

(i) Mg (ii) O₂

(a) Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.

Example: CuSO₄ (aq) + Zn (s) ZnSO₄ + Cu

When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained. In this reaction, zinc displaces copper from copper sulphate compound so that copper is set free. The blue colour of copper sulphate solution fades due to the formation of zinc sulphate.

(b) Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.

Example: AgNO₃ (aq) + NaCl (aq) AgCl (s)+ NaNO₃ (aq)

When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed alongwith sodium nitrate solution. In this reaction, two compounds, silver nitrate and sodium chloride, react to form two new compounds, silver chloride and sodium nitrate.

Those reactions in which a compound splits up into two or more simpler substances are known as decomposition reactions.

Example: When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

They are called opposite of combination reactions because in a combination reaction, two or more substances combine to form a single substance.

Example: Magnesium and oxygen combine, when heated, to form magnesium oxide.

(b) Cu (s) + 2AgNO₃ (aq) Cu(NO₃)₂ (aq) + 2Ag (s)

(a) When a piece of iron metal is placed in copper sulphate solution, then magnesium sulphate solution and copper metal are formed. This is a type of displacement reaction.

(b)

(a) H₂

(b) CuO

(c) CuO

(d) H₂

When silver nitrate solution is added to sodium chloride solution, then a white precipitate of silver chloride is formed alongwith sodium nitrate solution.

(a) AgNO₃ (aq) + NaCl (aq) AgCl (s)+ NaNO₃ (aq)

(b) Double displacement reaction.

When silver chloride is exposed to light, it decomposes to form silver metal and chlorine gas.

This reaction is used in black and white photography.

When a strip of zinc metal is placed in copper sulphate solution, then zinc sulphate solution and copper are obtained.

(b) Displacement reaction.

(a) Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a chemical (such as an acid) on their surface. Rusting of iron metal is the most common form of corrosion.

During the corrosion of iron, iron metal is oxidised by the oxygen of air in the presence of water (moisture) to form hydrated iron oxide called rust.

(b) Rusting.

(c) Oxidation.

(d) Railings, car bodies and bridges.

(a) The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called rancidity. It spoils the food materials prepared in fats and oils which have been kept for a considerable time and makes them unfit for eating.

(b) Oxidation.

(c) (i) Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils.

(ii) It can be prevented by packaging fat and oil containing foods in nitrogen gas.

(iii) Rancidity can be retarded by keeping food in a refrigerator.

(iv) Rancidity can be prevented by storing food in air-tight containers.

(v) Storing foods away from light can also prevent rancidity.

(a) When barium chloride solution is added to sodium sulphate solution, then a white precipitate of barium sulphate is formed alongwith sodium chloride solution.

(b)

(c) Solid sodium sulphate and Solid barium chloride

(d) Double displacement reaction.

(e) Double displacement reaction between silver nitrate solution and sodium chloride solution forms a white precipitate of silver chloride and sodium nitrate solution.

(a) Ferrous sulphate.

(b) Decomposition reaction.

(c)

(a) Lead nitrate.

(b) Nitrogen dioxide.

(c)

(a) Combination reaction.

(b) Decomposition reaction.

(a) Zinc (Zn)

(b) Copper (Cu)

(c) Copper sulphate (CuSO₄)

(d) Displacement reaction;

CuSO₄ (aq) + Zn (s) ZnSO₄ (aq) + Cu (s)

(e) Brass

(a) Copper (Cu)

(b) Hydrogen (H₂)

(c) Copper oxide (CuO)

(d) Water (H₂O)

(e) CuO + H₂ Cu + H₂O

(f) Displacement reaction (which is also a redox reaction).

(a) Silver (Ag)

(b) Silver nitrate (AgNO₃)

(c) Silver chloride (AgCl)

(d) AgNO₃(aq) + NaCl (aq) AgCl (s) + NaNO₃ (aq)

(e) Double displacement reaction.

(a) Metal X : Copper; Metal Y : Sodium

(b) Copper sulphate, CuSO₄

(c) Sodium sulphate, Na₂SO₄

(d) Barium sulphate, BaSO₄

(e) Copper chloride, CuCl₂

(a) Copper sulphate.

(b) Blue colour.

(c) Copper sulphide.

(d) CuSO₄ (aq) + H₂S (g) CuS (s) + H₂SO₄ (aq)

(e) Double displacement reaction.

(a) Copper.

(b) Silver nitrate.

(c) Silver.

(d) Copper nitrate.

(e) Displacement reaction.

(a) Silver.

(b) Chlorine.

(c) Silver chloride.

(d) Silver nitrate and Sodium chloride.

(e) Decomposition reaction;