Chemical Changes in Chemistry

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Chemical Changes in Chemistry

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(i) Combination Reactions : Combination reactions occur when two substances unite to form a third substance.

For example, combining magnesium (Mg) and oxygen (O2) result in the production of magnesium oxide (MgO)

2Mg + O2=> 2MgO

This ereaction can be accomplished by burning magnesium in air, which supplied the oxygen.

(ii) Decomposition Reaction : Decomposition reaction occurs when a single compound breaks down into two or more simpler substances.

In the decomposition of mercuric oxide (HgO), the elements mercury (Hg) and oxygen (O2) are produced.

2HgO=> 2Hg + O2

(iii) Displacement Reaction : When one element replaces another in a compound, it is known as a displacement reaction.

For example, iron (Fe) may displace copper (Cu) in a solution of cupric sulphate (CuSO4).

Fe + CuSO4=> FeSO4 + Cu

(iv) Double Decomposition Reactions : When two compounds interact to form two other compounds, it is known as a double decomposition reaction.

For example, Sodium iodide (Nal) and lead nitrate (Pb(NO3)2) react to form lead iodide (Pbl2) and sodium nitrate (2NaNO3).

2NaI + Pb(NO3)2=> Pbl2 + 2NaNO3

(v) Hydrolysis : Hydrolysis is a double decomposition reaction in which water reacts with a second substance.

When ammonium chloride (NH4Cl) is combined with water (H2O), it undergoes hydrolysis, yielding ammonium hydroxide (NH4OH) and hydrochloric acid (HCl).

NH4Cl + H2O=> NH4OH + HCl

(vi) Neutralization Reactions : Neutralization is the interaction of an acid with an equivalent quantity of a base.

If the process is carried out in an aqueous solution (dissolved in water), the products are water and a salt.

For example, hydrochloric acid (HCl) and sodium hydroxide (NaOH) neutralize each other when dissolved in water, forming sodium chloride (NaCl), a salt, and water (H2O).

HCl + NaOH -> NaCl + H2O

(vii) Substitution Reaction : Substitution reactions occur when an element, such as chlorine (Cl), replaces one or more hydrogen atoms in a hydrocarbon, such as methane (CH4).

CH4 + Cl2=> CH3Cl + HCl

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