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This unit is designed to help you understand the difference between reversible and

irreversible reactions.

List of irreversible reactions :

1. neutralisation between acids and bases

2. dissociation of strong acid

3. dissociation of strong base

4. dissociation of soluble salt

List of reversible reactions :

1. dissociation of weak acid

2. dissociation of conjugate base

3. dissociation of weak base

4. dissociation of conjugate acid

5. dissociation of insoluble salt

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Examples of irreversible reactions :

1. neutralisation between acids and bases

NaOH + HCl → NaCl + H2O

2. dissociation of strong acid

HCl → H+ + Cl

-

3. dissociation of strong base

KOH → K+ + OH

-

4. dissociation of soluble salt

MgCl2 (aq) → Mg2+

(aq) + 2 Cl-(aq)

Examples of reversible reactions :

1. dissociation of weak acid

CH3COOH ⇌ H+ + CH3COO

-

2. dissociation of conjugate base

CH3COO- + H2O ⇌ OH

- + CH3COOH

3. dissociation of weak base

NH3 + H2O ⇌ NH4+ + OH

-

4. dissociation of conjugate acid

NH4+ ⇌ NH3 + H

+

5. dissociation of insoluble salt

AgCl(s) ⇌ Ag+(aq) + Cl

-(aq)

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Exercise 01 : Complete the equation by adding → or ⇌ sign

Chemical Equation Type of reaction

H2SO4 2 H+ + SO4

2-

HCl H+ + Cl

-

CH3COOH H+ + CH3COO

-

H3PO4 H+ + H2PO4

-

HNO3 H+ + NO3

-

HBr H+ + Br

-

HF H+ + F

-

HClO4 H+ + ClO4

-

H2S H+ + HS

-

C6H5COOH H+ + C6H5COO

-

Answer :

Chemical Equation Type of reaction

H2SO4 → H+ + HSO4

-

Dissociation of strong acid

HCl → H+ + Cl

-

Dissociation of strong acid

CH3COOH ⇌ H+ + CH3COO

-

Dissociation of weak acid

H3PO4 ⇌ H+ + H2PO4

-

Dissociation of weak acid

HNO3 → H+ + NO3

-

Dissociation of strong acid

HBr → H+ + Br

-

Dissociation of strong acid

HF ⇌ H+ + F

-

Dissociation of weak acid

HClO4 → H+ + ClO4

-

Dissociation of strong acid

H2S ⇌ H+ + HS

-

Dissociation of weak acid

C6H5COOH ⇌ H+ + C6H5COO

-

Dissociation of weak acid

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Exercise 02 : Complete the equation by adding → or ⇌ sign

Chemical Equation Type of reaction

NaOH Na+ + OH

-

NH3 + H2O NH4+ + OH

-

C6H5NH2 + H2O C6H5NH3+ + OH

-

LiOH Li+ + OH

-

N2H4 + H2O N2H5+ + OH

-

KOH K+ + OH

-

CH3NH2 + H2O CH3NH3+ + OH

-

CH3CH2NH2 + H2O CH3CH2NH3+ + OH

-

Answer :

Chemical Equation Type of reaction

NaOH → Na+ + OH

-

Dissociation of strong base

NH3 + H2O ⇌ NH4+ + OH

-

Dissociation of weak base

C6H5NH2 + H2O ⇌ C6H5NH3+ + OH

-

Dissociation of weak base

LiOH → Li+ + OH

-

Dissociation of strong base

N2H4 + H2O ⇌ N2H5+ + OH

-

Dissociation of weak base

KOH → K+ + OH

-

Dissociation of strong base

CH3NH2 + H2O ⇌ CH3NH3+ + OH

-

Dissociation of weak base

CH3CH2NH2 + H2O ⇌ CH3CH2NH3+ + OH

-

Dissociation of weak base

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Exercise 03 : Complete these salt dissociation equation.

Add also → or ⇌ sign.

Chemical Equation Type of reaction

MgCl2 (aq) → Mg2+

(aq) + 2 Cl-(aq)

Dissociation of soluble salt

BaSO4 (s) 2+

(aq) + 2-

(aq)

CaCO3 (s) 2+

(aq) + 2-

(aq)

Pb(NO3)2 (aq) 2+

(aq) + -(aq)

BaCO3 (s) 2+

(aq) + 2-

(aq)

FeSO4 (aq) 2+

(aq) + 2-

(aq)

AgCl(s) +(aq) +

-(aq)

PbCl2 (s) 2+

(aq) + -(aq)

Answer :

Chemical Equation Type of reaction

MgCl2 (aq) → Mg2+

(aq) + 2 Cl-(aq)

Dissociation of soluble salt

BaSO4 (s) ⇌ Ba2+

(aq) + SO42-

(aq) Dissociation of insoluble salt

CaCO3 (s) ⇌ Ca2+

(aq) + CO32-

(aq) Dissociation of insoluble salt

Pb(NO3)2 (aq) → Pb2+

(aq) + 2 NO3-(aq)

Dissociation of soluble salt

BaCO3 (s) ⇌ Ba2+

(aq) + CO32-

(aq) Dissociation of insoluble salt

FeSO4 (aq) → Fe2+

(aq) + SO42-

(aq) Dissociation of soluble salt

AgCl(s) ⇌ Ag+(aq) + Cl

-(aq)

Dissociation of insoluble salt

PbCl2 (s) ⇌ Pb2+

(aq) + 2 Cl-(aq)

Dissociation of insoluble salt

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Exercise 04 : Complete these weak acid and conjugate base dissociation

equation.

Chemical Equation Type of reaction

HF ⇌ H+ + F

-

Dissociation of weak acid

F- + H2O ⇌ HF + OH

-

Dissociation of conjugate base

H2S ⇌ + Dissociation of weak acid

HS- + H2O ⇌ +

Dissociation of conjugate base

CH3COOH ⇌ + Dissociation of weak acid

CH3COO- + H2O ⇌ +

Dissociation of conjugate base

C6H5COOH ⇌ + Dissociation of weak acid

C6H5COO- + H2O ⇌ +

Dissociation of conjugate base

Answer :

Chemical Equation Type of reaction

HF ⇌ H+ + F

-

Dissociation of weak acid

F- + H2O ⇌ HF + OH-

Dissociation of conjugate base

H2S ⇌ H+ + HS

-

Dissociation of weak acid

HS- + H2O ⇌ H2S + OH

-

Dissociation of conjugate base

CH3COOH ⇌ H+ + CH3COO

-

Dissociation of weak acid

CH3COO- + H2O ⇌ CH3COOH + OH

-

Dissociation of conjugate base

C6H5COOH ⇌ H+ + C6H5COO

-

Dissociation of weak acid

C6H5COO- + H2O ⇌ C6H5COOH + OH

-

Dissociation of conjugate base

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Exercise 05 : Complete these equations of dissociation of weak base and acid

conjugate.

Chemical Equation Type of reaction

NH3 + H2O ⇌ NH4+ + OH

-

Dissociation of weak base

NH4+ ⇌ NH3 + H

+

Dissociation of conjugate

acid

C6H5NH2 + H2O ⇌ + OH-

C6H5NH3+ ⇌ + H

+

N2H4 + H2O ⇌ + OH-

N2H5+ ⇌ + H

+

CH3NH2 + H2O ⇌ + OH-

CH3NH3+ ⇌ + H

+

CH3CH2NH2 + H2O ⇌ + OH-

CH3CH2NH3+ ⇌ + H

+

Answer :

Chemical Equation Type of reaction

NH3 + H2O ⇌ NH4+ + OH

-

Dissociation of weak base

NH4+ ⇌ NH3 + H

+

Dissociation of conjugate

acid

C6H5NH2 + H2O ⇌ C6H5NH3+ + OH

-

Dissociation of weak base

C6H5NH3+ ⇌ C6H5NH2 + H

+

Dissociation of conjugate

acid

N2H4 + H2O ⇌ N2H5+ + OH

-

Dissociation of weak base

N2H5+ ⇌ N2H4 + H

+

Dissociation of conjugate

acid

CH3NH2 + H2O ⇌ CH3NH3+ + OH

-

Dissociation of weak base

CH3NH3+ ⇌ CH3NH2 + H

+

Dissociation of conjugate

acid

CH3CH2NH2 + H2O ⇌ CH3CH2NH3+ + OH

-

Dissociation of weak base

CH3CH2NH3+ ⇌ CH3CH2NH2 + H

+

Dissociation of conjugate

acid

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Exercise 06 : Complete these equations by adding → or ⇌ sign.

Chemical Equation Type of reaction

H3PO4 + NaOH NaH2PO4 +H2O

NaH2PO4 + NaOH Na2HPO4 +H2O

Na2HPO4 + NaOH Na3PO4 +H2O

NaOH Na+ + OH

-

H3PO4 H2PO4- + H

+

H2PO4- HPO4

2- + H

+

HPO42-

PO43-

+ H+

PO43-

+ H2O HPO42-

+ OH-

HPO42-

+ H2O H2PO4- + OH

-

H2PO4- + H2O H3PO4 + OH-

Na3PO4 3 Na+

+ PO43-

Answer :

Chemical Equation Type of reaction

H3PO4 + NaOH → NaH2PO4 +H2O Neutralisation

NaH2PO4 + NaOH → Na2HPO4 +H2O Neutralisation

Na2HPO4 + NaOH → Na3PO4 +H2O Neutralisation

NaOH → Na+ + OH

-

Dissociation of strong base

H3PO4 ⇌ H2PO4- + H

+

Dissociation of weak acid

H2PO4- ⇌ HPO4

2- + H

+

Dissociation of weak acid

HPO42-

⇌ PO43-

+ H+

Dissociation of weak acid

PO43-

+ H2O ⇌ HPO42-

+ OH-

Dissociation of conjugate base

HPO42-

+ H2O ⇌ H2PO4- + OH

-

Dissociation of conjugate base

H2PO4- + H2O ⇌ H3PO4 + OH-

Dissociation of conjugate base

Na3PO4 → 3 Na+

+ PO43-

Dissociation of soluble salt

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Exercise 07 : Complete these equations by adding the product.

Chemical Equation Type of reaction

NH3 + HCl →

NH4Cl + NaOH → + +

NH4Cl(s) → (aq) + (aq)

HCl → +

NH3+ H2O ⇌ +

NH4+ ⇌ +

Answer :

Chemical Equation Type of reaction

NH3 + HCl → NH4Cl Neutralisation

NH4Cl + NaOH → NH3 + H2O +NaCl Neutralisation

NH4Cl(s) → NH4+(aq) + Cl

-(aq)

Dissociation of soluble salt

HCl → H+ + Cl

-

Dissociation of strong acid

NH3+ H2O ⇌ NH4+ + OH

-

Dissociation of weak base

NH4+ ⇌ NH3 + H

+

Dissociation of conjugate acid

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Exercise 08 : Complete these equations by adding the product.

Chemical Equation Type of reaction

CH3COOH + KOH → +

CH3COOK + HCl → +

CH3COOK(s) → +

KOH → +

CH3COO- + H2O ⇌ +

CH3COOH ⇌ +

Answer :

Chemical Equation Type of reaction

CH3COOH + KOH → CH3COOK + H2O Neutralisation

CH3COOK + HCl → CH3COOH + KCl Neutralisation

CH3COOK(s) → CH3COO-(aq) + K

+(aq)

Dissociation of soluble salt

KOH → K+ + OH

-

Dissociation of strong acid

CH3COO- + H2O ⇌ CH3COOH + OH

-

Dissociation of weak base

CH3COOH ⇌ CH3COO- + H

+

Dissociation of conjugate acid

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Exercise 09 : Complete these equations by adding the product.

Chemical Equation Type of reaction

KBr → K+ +

C6H5COOH ⇌ + H+

Fe(OH)2 ⇌ Fe2+

+

AgOH + HNO3 → + H2O

PbI2 ⇌ Pb2+

+

C6H5NH3+ ⇌ + H

+

C6H5NH3Cl + KOH → + KCl

BaSO4 ⇌ Ba2+

+

C2H5COONa + HNO3 → + NaNO3

HI → + I-

KOH → + OH-

Answer :

Chemical Equation Type of reaction

KBr → K+ + Br

-

Dissociation of strong base

C6H5COOH ⇌ C6H5COO- + H

+

Dissociation of weak acid

Fe(OH)2 ⇌ Fe2+

+ 2 OH-

Dissociation of weak base

AgOH + HNO3 → AgNO3 + H2O Neutralisation

PbI2 ⇌ Pb2+

+ 2 I-

Dissociation of insoluble salt

C6H5NH3+ ⇌ C6H5NH2 + H

+

Dissociation of conjugate acid

C6H5NH3Cl KOH → C6H5NH2 + KCl Neutralisation

BaSO4 ⇌ Ba2+

+ SO42-

Dissociation of insoluble salt

C2H5COONa + HNO3 → C2H5COOH + NaNO3 Neutralisation

HI → H+ + I

-

Dissociation of strong acid

KOH → K+ + OH

-

Dissociation of strong base

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Exercise 10 Write the chemical equations of these reactions : 1. dissociation of NaOH

→

2. neutralisation between KOH and

CH3COOH

→

3. dissociation of CaCO3

⇌

4. dissociation of C6H5NH2

⇌

5. dissociation of C6H5NH3NO3

→

6. neutralisation between NH3 and H2SO4

→

7. dissociation of CH3COOK

→

Answer :

1. dissociation of NaOH

NaOH → Na+ + OH

-

2. neutralisation between KOH and

CH3COOH

KOH + CH3COOH → CH3COOK + H2O

3. dissociation of CaCO3

CaCO3 ⇌ Ca2+

+ CO32-

4. dissociation of C6H5NH2

C6H5NH2 + H2O ⇌ C6H5NH3+ + OH

-

5. dissociation of C6H5NH3NO3

C6H5NH3NO3 → C6H5NH3+ + NO3

-

6. neutralisation between NH3 and H2SO4

2 NH3 + H2SO4 → (NH4)2SO4

7. dissociation of CH3COOK

CH3COOK → CH3COO- + K

+