Column A Column B (i) Reactants (a) The substances that are formed as a result of chemical reaction. (ii) Products (b) The substances in which chemical change is brought. (iii) Exothermic (c) Reactions in which the products do not react to give back the reactants. (iv) Endothermic (d) Reactions which are accompanied with evolution of heat. (v) Reversible (e) Reactions which are accompanied with absorption of heat. (vi) Irreversible (f) Reactions which can take place in both the directions under similar conditions of temperature and pressure (vii) Oxidation (g) The process of addition of hydrogen or removal of oxygen (viii) Reduction (h) Reaction in which two or more substances combine to form a new single substance (ix) Combination (i) The process of addition of oxygen or removal of hydrogen. (x) Decomposition (j) Reaction in which one of the products formed is an insoluble substance and is thrown out of the solution as solid. (xi) Displacement (k) The conversion of a single compound into two or more simpler substances. (xii) Precipitation (l) Reaction in which an element displaces another element from its compound. (xiii) Double displacement (m) Reaction in which two reacting compounds exchange their corresponding ions and form two new compounds. (xiv) Oxidising agent (n) A substance which provides hydrogen or removes oxygen. (xv) Reducing agent (o) A substance which provides oxygen or removes hydrogen.

The substances that are formed as a result of a chemical reaction are called products. For example, water is the product of the reaction between hydrogen and oxygen. The substances in which chemical change is brought are called reactants. The chemical composition of the reactants may change and the elements within them may recombine into new substances. The reactions which are accompanied by the evolution of heat are known as exothermic reactions. This heat is released into the surroundings, resulting in an overall negative enthalpy of the reaction. Endothermic reactions are accompanied by the absorption of heat. When nitrogen and oxygen are heated together to a temperature of about 3000 ° C , nitric oxide is formed, it is an endothermic reaction, as heat is absorbed. Reversible reactions are reactions that can take place in both directions under similar conditions of temperature and pressure. One example of a reversible reaction is the reaction of hydrogen gas and iodine vapour to form hydrogen iodide. Irreversible reactions are reactions in which the products do not react to give back the reactants. For example, combustion reactions are generally irreversible. In combustion, the fuel combines with oxygen (in the air) and produces carbon dioxide and water vapour and cannot be turned back into fuel again. Oxidation is a chemical reaction involving the addition of oxygen to a substance or the removal of hydrogen from a substance. Oxidation is the loss of electrons or an increase in the oxidation state of an atom, an ion, or of certain atoms in a molecule. Reduction is the process of addition of hydrogen to a substance or removal of oxygen from a substance. Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion. Combination reactions are the reactions in which two or more substances combine to form a new single substance. Combination reaction is also known as a synthesis reaction. Decomposition reactions involve the conversion of a single compound into two or more simpler substances. Decomposition reactions are usually endothermic because they involve breaking of bonds by absorbing energy from external source in the form of heat or light. Displacement reactions are the reactions in which a high reactive element displaces a less reactive element from its compound. The products of a displacement reaction can be predicted from the reactivity series of the metals. Precipitation reactions are the reactions in which one of the products formed is an insoluble substance and is thrown out of the solution as solid. The insoluble salt that falls out of the solution is known as the precipitate. Silver nitrate and potassium chloride is a precipitation reaction because solid silver chloride is formed as a product of the reaction. Double displacement reactions are the reactions in which two reacting compounds exchange their corresponding ions and form two new compounds. For example, Na 2 S + 2 HCl → 2 NaCl + H 2 S An oxidising agent is a substance that provides oxygen or removes hydrogen. The oxidising agent itself undergoes reduction. A reducing agent is a substance that provides hydrogen or removes oxygen. The reducing agent itself undergoes oxidation. Column A Column B (i) Reactants (b) The substances in which chemical change is brought. (ii) Products (a) The substances that are formed as a result of chemical reaction. (iii) Exothermic (d) Reactions which are accompanied with evolution of heat. (iv) Endothermic (e) Reactions which are accompanied with absorption of heat. (v) Reversible (f) Reactions which can take place in both the directions under similar conditions of temperature and pressure (vi) Irreversible (c) Reactions in which the products do not react to give back the reactants. (vii) Oxidation (i) The process of addition of oxygen or removal of hydrogen. (viii) Reduction (g) The process of addition of hydrogen or removal of oxygen (ix) Combination (h) Reaction in which two or more substances combine to form a new single substance (x) Decomposition (k) The conversion of a single compound into two or more simpler substances. (xi) Displacement (l) Reaction in which an element displaces another element from its compound. (xii) Precipitation (j) Reaction in which one of the products formed is an insoluble substance and is thrown out of the solution as solid. (xiii) Double displacement (m) Reaction in which two reacting compounds exchange their corresponding ions and form two new compounds. (xiv) Oxidising agent (o) A substance which provides oxygen or removes hydrogen. (xv) Reducing agent (n) A substance which provides hydrogen or removes oxygen.

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The chemical formula of aluminium sulphate is ${Al}_{3} {({SO}_{4})}_{2}$ .

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Important Questions on Chemical Reactions and Equations

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 7

Rusting of iron and rancidity are caused due to oxidation.

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 8

The term 'aqueous' represents excess of water.

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 9

Colour of copper sulphate remains unchanged when an iron nail is dipped in it.

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 10

A chemical change cannot be reversed.

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Match the Columns

Column A	Column B
(i) Reactants	(a) The substances that are formed as a result of chemical reaction.
(ii) Products	(b) The substances in which chemical change is brought.
(iii) Exothermic	(c) Reactions in which the products do not react to give back the reactants.
(iv) Endothermic	(d) Reactions which are accompanied with evolution of heat.
(v) Reversible	(e) Reactions which are accompanied with absorption of heat.
(vi) Irreversible	(f) Reactions which can take place in both the directions under similar conditions of temperature and pressure
(vii) Oxidation	(g) The process of addition of hydrogen or removal of oxygen
(viii) Reduction	(h) Reaction in which two or more substances combine to form a new single substance
(ix) Combination	(i) The process of addition of oxygen or removal of hydrogen.
(x) Decomposition	(j) Reaction in which one of the products formed is an insoluble substance and is thrown out of the solution as solid.
(xi) Displacement	(k) The conversion of a single compound into two or more simpler substances.
(xii) Precipitation	(l) Reaction in which an element displaces another element from its compound.
(xiii) Double displacement	(m) Reaction in which two reacting compounds exchange their corresponding ions and form two new compounds.
(xiv) Oxidising agent	(n) A substance which provides hydrogen or removes oxygen.
(xv) Reducing agent	(o) A substance which provides oxygen or removes hydrogen.

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 1

Why should a magnesium ribbon be cleaned before being burnt in air?

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 2

Which type of reaction takes place when magnesium ribbon burns in the air? Why is it called so?

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Science Chemistry>Chapter 1 - Chemical Reactions and Equations>ASSESSMENT>Q 3

Why does the red litmus paper turn blue when touched with an aqueous solution of magnesium oxide?

The chemical formula of aluminium sulphate is Al3(SO4)2.

Important Questions on Chemical Reactions and Equations

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The chemical formula of aluminium sulphate is ${Al}_{3} {({SO}_{4})}_{2}$ .