Chemical Reactions PDF

# CHAPTER 6 CHEMICAL REACTIONS ## Learning Outcomes: - Describe different types of chemical reactions. - Identify the type of reaction. - Identify the effect of some metals on oxides. ## LATEST SYLLABUS - Key Concepts / Concerns - Reactivity series: In reactivity series metals are arranged in order of their reactivity. - The metal that displaces the metal ion from the solution is more reactive. - Predict the reactivity of metals. - Endothermic & exothermic reactions. Neutralization reaction. - Decomposition - reactions forming oxides. - Classification of oxides: - Acidic - Basic - Amphoteric - Neutral - Metal oxides - basic; nonmetal oxides - acidic in nature. - Acidic oxides react with bases, basic oxides react with acids. - Oxides such as ZnO, PbO react both with acids & bases. These are amphoteric oxides. ## A. CHEMICAL REACTIONS - Introduction ### TERM - A chemical reaction is a chemical change in which matter changes into a new substance or substances. - A chemical reaction is often accompanied by external indications or characteristics. ### INDICATIONS - Accompanying a chemical reaction - **a] CHANGE OF - Colour** - Mercury [II] oxide ($2HgO$) + Heat → $2Hg$ + $O_2 (g)$. (The chemical reaction results in a colour change from Red to Silvery.) - **b] EVOLUTION OF - A Gas** - $Zn + 2HCl (dil.)$ → $ZnCl_2 + H_2 (g)$. (The chemical reaction results in the evolution of the gas, Hydrogen.) - **c] EVOLUTION OR ABSORPTION OF - Heat** - Exothermic reactions - Proceed with evolution of heat energy - represented as Δ - Endothermic reactions - Proceed with absorption of heat energy - represented as -Δ - Calcium oxide & water: $CaO + H_2O$ → $Ca(OH)_2 + Δ$ (This is an exothermic reaction.) - Nitrogen & oxygen: $N_2 + O_2$ → $2NO - Δ$ (This is an endothermic reaction.) - **d] FORMATION OF - Precipitate** - Certain chemical reactions characterized by formation of insoluble precipitate. - Silver nitrate and dil. hydrochloric acid: $AgNO_3 + HCl → HNO_3$ + $AgCl$ (The chemical reaction results in the formation of Silver chloride - milky white precipitate) ## B. CHEMICAL REACTIONS - Main reactions | Type | Reactants | Products | |---|---|---| | 1. DIRECT COMBINATION REACTION [synthesis] | A + B → AB Two (or more] reactants e.g. Iron + Sulphur → Iron sulphide Fe + S → FeS Reaction in which - two or more elements or compounds combine to give - One new compound | A B One new compound | | 2. DECOMPOSITION REACTION | AB → A + B One chemical compound e.g. Copper carbonate CuCO3 → Copper oxide + Carbon dioxide CuO + CO2 Reaction in which - a chemical compound decomposes into - two or more simpler substances. | A+B Two simpler substances [elements or compounds] | 3. DISPLACEMENT REACTION [substitution] | A + BC→ AC + B Element + Compound → New compound + Displaced element e.g. Zinc + Copper sulphate → Zinc sulphate + Copper Zn + CuSO4 → ZnSO4 + Cu Reaction in which - one element - displaces another element from its compound. | AC New compound + B Displaced element | | 4. DOUBLE DECOMPOSITION REACTION | A+B- + C+D- → A+D- + C+B- Compound + Compound → New compound + New compound e.g. Silver nitrate + Potassium chloride → Silver chloride + Potassium nitrate AgNO3 + KCl → AgCl + KNO3 Reaction in which both reactants - are decomposed by exchanging their radicals to give - newcompounds. | A+D- New compound + C+B- New compound | ## C. CHEMICAL REACTIONS - Types of reactions ### 1. DIRECT COMBINATION REACTIONS [Synthesis] - Direct combination reactions are also called - 'Synthesis' reaction. - It is a chemical reaction in which - - a] Two or more elements - combine - to form a compound: A + B → AB. - b] An element - combines with a compound - to form a new compound: Compound + Element → New compound. - c] Two or more compounds - combine - to form a new compound: Compound + Compound → New compound. #### EXAMPLES: - **a] ELEMENT + ELEMENT → COMPOUND** - Metal + Oxygen → Metallic oxide. - $4Na + O_2 → 2Na_2O$ - $2Ca + O_2 → 2CaO$ - Non-metal + Oxygen→ Non-metallic oxide: - $C + O_2 → CO_2$ - $S + O_2 → SO_2$ - $4P + 5O_2 → 2P_2O_5$ - **b] COMPOUND + ELEMENT → NEW COMPOUND** - $2CO + O_2 → 2CO_2$ - $2SO_2 + O_2 → 2SO_3$ - **c] COMPOUND + COMPOUND → NEW COMPOUND** - Metallic oxide + Water → Base [alkali] - $Na_2O + H_2O → 2NaOH$ - $CaO + H_2O → Ca(OH)_2$ - Non-metallic oxide + Water → Acid - $CO_2 + H_2O → H_2CO_3$ - $SO_2 + H_2O → H_2SO_3$ - $P_2O_5 + 3H_2O → 2H_3PO_4$ ## 2. DECOMPOSITION REACTION - It is a chemical reaction in which a compound decomposes - - a] To give - two elements: - AB → A + B. - b] To give - one new compound & a new element: - AB → New compound + Element. - c] To give - two new compounds: - AB → New compound + New compound. #### EXAMPLES: ### THERMAL DECOMPOSITION - A decomposition reaction which is brought about - by heat - **a] COMPOUND → ELEMENT** - Metallic oxide → Metal + Oxygen. - $2HgO$ → $2Hg + O_2$ - $2Ag_2O$ → $4Ag + O_2$ - **b] COMPOUND → NEW COMPOUND + ELEMENT** - $2KNO_3$ → $2KNO_2 + O_2$ - $2KClO_3$ → $2KCl + 3O_2$ - **c] COMPOUND → NEW COMPOUND + NEW COMPOUND** - $CaCO_3 $ → $CaO + CO_2$ - $Zn(OH)_2$ → $ZnO + H_2O$ ### THERMAL DISSOCIATION - It is a decomposition reaction - in which a substance dissociates into two or more simpler substances - on application of heat. e.g. $NH_4Cl $ _heat_ $NH_3 + HCl$. - Thermal dissociation unlike thermal decomposition is a - reversible reaction. ### ELECTROLYTIC DECOMPOSITION - A decomposition reaction which is brought about - by passage of electric current. - e.g. $2H_2O $ _electric current_ $2H_2 + O_2$. ### PHOTOCHEMICAL DECOMPOSITION - A decomposition reaction which occurs - in the presence of light. - e.g. decomposition of silver salts - in presence of sunlight. ## 3. DISPLACEMENT REACTION - It is a chemical reaction in which - - An element placed higher in the activity series - displaces the element placed below it - from a solution of its compound. - A + BC → AC + B - Element displaces Compound → New compound + Displaced element - e.g. Zinc + Copper sulphate → Zinc sulphate + Copper - $Zn + CuSO_4 → ZnSO_4 + Cu $ ## 4. DOUBLE DECOMPOSITION REACTION - It is a chemical reaction in which- - Both reactants [compounds] are decomposed to give - two new compounds - by exchanging their radicals. - $AB + C+D- → A+D- + C+B-$ ### a] NEUTRALIZATION REACTIONS - Reactions between two compounds - base & acid to give two new compounds - salt & water by interchange of their radicals. - Base + Acid → Salt + Water - $Na^+ OH^- + H^+ Cl^- → Na^+ Cl^- + H^+ OH^-$ - $i.e. NaOH + HCl→ NaCl + H_2O$ ### b] PRECIPITATION REACTIONS - Reactions between two compounds - in solution state to give two new compounds - one of which is insoluble - called precipitate. - Compound + Compound → New compound + Precipitate - $FeCl_3 + 3NaOH → 3NaCl + Fe(OH)_3↓ [reddish brown]$ - $Zn SO_4 + 2 NH_4OH → (NH_4)_2SO_4 + Zn(OH)_2 [gelatinous white]$ ## CHEMICAL REACTIONS - Reactivity series ### ACTIVITY SERIES - Of metals [displacement reactions] - It is a series of arrangement of metals - in order of their reactivity. - The most active metal - is at the top of the series. - The least active metal - is at the bottom of the series. - The properties of metals - are related to their activity series. | Metal | Activity Reaction | Observation | Equation | |---|---|---|---| | **WATER** K & Na | K, Na - React - violently with cold water. | 2K +2H2O→ 2KOH + H₂ | Ca | Reacts - less vigorously with cold water. | Ca +2H2O → Ca(OH)2+H2 | | Mg to Fe | Mg to Fe - React - smoothly with water [steam] | 3Fe+4H2O → Fe3O4 +4H2 | | Below [H] | Below [H] - Do not react with water or steam displacing hydrogen from it. | | | **ACIDS** K & Na | K & Na - React - explosively with HCl or. dil. H2SO4. Ca to Fe - React - less vigorously with decreasing vigour with dil. HCl or dil. H2SO4. | 2K + 2HCl → 2KCl +H₂ Ca + 2HCl → CaCl₂ +H₂ | | Below [H] | Below [H] - Do not react - with dil. acids - displacing hydrogen. | | | **AIR** K to Ag | K to Ag - React with - oxygen to form - metallic oxides. | 4K + O2 → 2K2O 3Fe + 202 → Fe3O4 | | Pt, Au | Pt, Au - Do not form - oxides | | ### DISPLACEMENT REACTIONS - Any metal in the reactivity series - displaces another metal below it, from its aq. soln. e.g. - Zinc is above copper and hence - displaces copper from copper [II] sulphate soln. - $Zn + CuSO_4→ ZnSO_4 + Cu$ ## FACTORS - Which bring about chemical changes or reactions - Chemical reactions - involve breaking of existing bonds & formation of new bonds, with absorption or release of energy e.g. heat, light & takes place due to - collision of particles in close contact with one another or by supplying energy, i.e. - a] Heat - it initiates reacting particles to move faster & collide frequently. - b] Light energy - absorbed by the reactant molecules, making them more activated. - Other factors - which supply energy are - electricity, catalyst, pressure etc. ## 5. REVERSIBLE REACTION - It is a chemical reaction in which - - The products formed react together - to form the original reactants - depending on the conditions of the reaction. - Reactants → Products - $A+B $ → $C+D$ | Reactant/s | | | |---|---|---| | Sulphur dioxide & oxygen | 2SO2 + O2 | 2SO3 _450°C_ Δ | | Iron & steam | 3Fe + 4H2O | Fe3O4 + 4H2 _Δ_ | | Calcium carbonate [heat] | CaCO3 | CaO + CO2 _Δ_ Fe | | Nitrogen & hydrogen | N2 + 3H2 | 2NH3 _Δ_ 450°C | | Nitrogen & oxygen | N2 + O2 | 2NO _>3000°C_ Δ | | Hydrogen chloride | 2HCl | H2 + Cl2 _Δ_ >500°C | ## 6. CATALYTIC REACTION - It is a chemical reaction in which - - A catalyst is used to - alter the rate of the reaction - [a catalyst is a compound - which alters the rate of a reaction but does not take part in it]. - Reactant/s | Catalyst | - $2H_2O_2$ | $MnO_2$ | - $2SO_2 + O_2$ | $V_2O_5$ | - $N_2 + 3H_2$ | $Fe/Mo$ | - $4NH_3 +5O_2$ | $Pt$ | - **Positive catalyst:** It is a catalyst which - speeds up the rate of the reaction. e.g. all of above. - **Negative catalyst:** It is a catalyst which - reduces the rate of the reaction. e.g. alcohol. - **Promoter:** It is added to the catalyst - to increase its efficiency. e.g. molybdenum [Mo]. ### ENZYMES: - Present in the human body, function as catalysts & accelerate the rate of biochemical reactions. - Pepsin accelerates conversion of - proteins to amino acids in the stomach. ## 7. EXOTHERMIC & ENDOTHERMIC REACTIONS - **Exothermic reactions** - are chemical reactions which proceed with - evolution of heat energy. - **Endothermic reactions** - are chemical reactions which proceed with - absorption of heat energy. | Representation: | Reactants | Product/s | | |---|---|---|---| | Exothermic reactions | A + B | C + Δ | | Endothermic reactions | A + B | C -Δ | ### Examples of exothermic and endothermic reactions: - **Catalytic oxidation of sulphur dioxide:** - $2SO2 + O2_V2O5_ 2503_450°C_ Δ$ - **Addition of water to quicklime:** - $CaO + H_2O_Fe_ Ca(OH)_2 + Δ$ - **Formation of ammonia from N₂ & H2:** - $N_2 + 3H_2 _450-500°C_ 2NH_3 + Δ$ -**Passage of steam over heated coke:** - $C + H_2O_1000°C_steam_ CO + H_2 - Δ$ -**Passage of N₂ & O₂ through electric arc:** - $N_2 + O_2 _3000°C_ 2NO - Δ$ ## DECOMPOSITION REACTIONS- To form oxides - Chemical compound decomposes or splits - to give two or more simpler substances. - Thermal decomposition - decomposition brought about by - heat. | Metal | Metal carbonates | Metal nitrates | Metal hydroxides | |---|---|---|---| | K, Na | K, Na - carbonates - do not decompose. | K, Na - nitrates - decompose Δ | K, Na - hydroxides - do not decompose. | | Ca | Ca to Cu-carbonates- decompose to give - Metal oxide + CO2 CaCO3→ CaO+CO₂ | Ca to Cu - nitrates- decompose to give - Metal oxide + NO2 + O2 | Ca to Cu - hydroxides- decompose to give - Metal oxide + H₂O | | Mg | | Metal nitrate → Metalnitrite+ O2 2Ca(NO₃)₂→ 2CaO+ 4NO2 + O2 | Ca(OH)2→ CaO+ H₂O | | Al | | | | | Zn | | | | | Fe | | | | | Pb | | | | | [H] | | | | | Cu | | | | | Hg | Hg and Ag-carbonates - decompose to give - Metal + oxygen + CO2 | Hg and Ag - nitrates - decompose to give - Metal + NO2 + 02 | Hg and Ag-hydroxides - rarely formed. | | Ag | | | | - Activity series of metals - on the left represents- metals arranged according to their reactivity i.e. the most reactive metal at the top & the least reactive at the bottom. ## D. OXIDES ### 1. TERM - Oxides are binary compounds - of a metallic or nonmetallic element - with oxygen. ### 2. PREPARATION | Some methods | | Oxide formed | |---|---|---| | By direct combination | S + O2 → SO2 | [sulphur dioxide] | | | 2Zn + O2 → 2ZnO | [zinc oxide] | | By action of steam on a metal | 3Fe + 4H2O → Fe3O4 | [tri iron tetroxide] + 4H2 | | By heat on oxides | 2Pb304 → 6PbO | [lead monoxide] + O2 | | By heat on nitrates | 2Ca(NO3)2 → 2CaO | [calcium oxide] + 4NO2+O2 | | By heat on carbonates | CaCO3 → CaO | [calcium oxide] + CO2 | ### 3. CLASSIFICATION - Oxides are classified into - four main classes depending on their nature. - a] Acidic oxides - b] Basic oxides - c] Amphoteric oxides - d] Neutral oxides | | Acidic oxides | Basic oxides | Amphoteric oxides | Neutral oxide | |---|---|---|---|---| | OXIDES OF - | Nonmetals e.g. SO₂, CO₂ | Metals e.g. K₂O, CaO | Metals e.g. ZnO, PbO, Al₂O₃ | Nonmetals e.g. NO, CO | | REACT WITH - | Water - to give an - acid CO₂+H₂O→H₂CO₃ | Water - to give an - base CaO+H₂O→ Ca(OH)₂ | | | | REACT WITH - | Bases [alkalis] - to give - salt & water | Acids - to give - salt & water | Acids & Bases- to give - salt & water | Do not react similarly | ### MISCELLANEOUS OXIDES - Besides acidic, basic, amphoteric & neutral oxides there are - miscellaneous oxides e.g. Peroxides [Na2O2], Mixed oxides [Pb3O4, Fe3O4], Dioxides [PbO2]. ### AMPHOTERIC HYDROXIDES - They are hydroxides of metals which react with - acids & bases give salt and water e.g. Zinc hydroxide Zn(OH)2, lead hydroxide Pb(OH)2, aluminium hydroxide Al(OH). ## KEY WORDS - Chemical reaction: It is a chemical change in which matter changes into - a new substance or substances. It is often accompanied by external indications or characteristics. - Direct combination reaction: Reaction in which - two or more elements or compounds combine to give - one new compound. - Decomposition reaction: Reaction which - a chemical compound decomposes into - two or more simpler substances. - Displacement reaction: Reaction in which - one element - displaces another element from its compound. - Double decomposition reaction: Reaction in which both reactants - are decomposed by exchanging their radicals to give - new compounds. - Thermal decomposition reactions: It is a decomposition reaction which is brought about by - heat. - Thermal dissociation: It is a decomposition reaction - in which a substance dissociates into - two or more simpler substances - on application of heat. e.g. $NH_4Cl $ _heat_ $NH_3 + HCl$. Thermal dissociation unlike thermal decomposition is a - reversible reaction. - Electrolytic decomposition: It is a decomposition reaction which is brought about - by passage of electric current. e.g. $2H_2O $ _electric current_ $2H_2 + O_2$. - Photochemical decomposition: It is a decomposition reaction which occurs - in the presence of light. e.g. decomposition of silver salts - in presence of sunlight. - Neutralization reaction: It is a reaction between two compounds - base & acid to give two new compounds - salt & water by interchange of radicals. - Precipitation reaction: It is a reaction between two compounds - in an aqueous solution state - to give two new compounds - one of which is insoluble - called precipitate. - Activity series of metals: It is a series of arrangement of metals - in order of their reactivity. The most active metal - is at the top of the series. The least active metal - is at the bottom of the series. The properties of metals are related to their activity series. - Reversible reactions: It is a chemical reaction in which - the products formed react together - to form the original reactants - depending on the conditions of the reaction. - Catalytic reactions: It is a chemical reaction in which a catalyst is used to - alter the rate of the reaction [a catalyst is a compound - which alters the rate of a reaction but does not take part in it]. - Promoter: It is a substance which is added to the catalyst - to increase its efficiency. e.g. molybdenum [Mo]. - Exothermic reactions: Exothermic reactions - are chemical reactions which proceed with - evolution of heat energy. - Endothermic reactions: Endothermic reactions - are chemical reactions which proceed with - absorption of heat energy. - Oxides: Oxides are binary compounds - of a metallic or nonmetallic element - with oxygen. ## HIGHLIGHTS ### Chemical Reactions - A chemical reaction is a chemical change in which matter changes into a new substance or substances. It is often accompanied by external indications or characteristics: - Colour change - Evolution or absorption of heat - Evolution of gas - Formation of precipitate - Examples: - 2HgO _heat_ 2Hg + O2 (gas evolved) - $Mg + 2HCl (dil.)$ → $MgCl_2$ + $H_2 (g) $ (gas evolved) - $CaO + H_2O$ → $Ca(OH)_2$ + Δ (heat evolved) - $N_2 + O_2$ → $2NO - Δ$ (heat absorbed) - $AgNO_3$ + $HCl$ → $HNO_3$ + $AgCl$ (silver chloride - white) ### Types of reactions - **a] Direct combination reactions** - Two or more elements or compounds combine to give one new compound. - $4Na + O2$ → $2Na_2O$ - **b] Decomposition reaction** - Compound decomposes to give two or more simpler substances. - Thermal decomposition - decomposition reaction brought about by - heat: - 2HgO _heat_ 2Hg + O2 - Thermal dissociation - reversible thermal decomposition reaction: - $NH_4Cl $ _heat_ $NH_3 + HCl$ - Electrolytic decomposition - reaction which occurs in - presence of light: - $2H_2O $ _electric current_ $2H_2 + O_2$ - Photochemical decomposition - reaction which occurs in - presence of light: - Decomposition of silver salts in presence of sunlight. - **c] Displacement reaction** - Reaction in which an element placed higher in the activity series displaces the element placed below it. - $Zn + CuSO_4$ → $ZnSO_4$ + Cu - **d] Double decomposition reaction** - Reaction in which both reactants are decomposed to give two new compounds - by exchanging their radicals: - $NaOH + HCl$ → $NaCl + H_2O$ (salt + water) - $FeCl_3 + 3NaOH$ → $3NaCl$ + $Fe(OH)_3$ (reddish brown ppt.) -**Neutralization reaction** - reaction between two compounds - acid and base to give salt & water. - $NaOH + HCl$ → $NaCl + H_2O$ - $FeCl_3 + 3NaOH$ → $3NaCl + Fe(OH)_3↓$ - **Precipitation reaction** - reaction between two compounds [in aq. soln. state] to give two new compounds - one of which is insoluble - called precipitate. - $FeCl_3 + 3NaOH$ → $3NaCl$ + $Fe(OH)_3↓$ - **e] Reversible reaction** - Reaction in which the products formed react together to give - original reactants. - $3Fe + 4H_2O $ _Δ_ $Fe_3O_4 + 4H_2$ - **f] Catalytic reaction** - Reaction in which a catalyst is used to - alter the rate of the reaction. - $2SO_2 + O_2 _V2O5_ 2503_450°C_ Δ$ (*catalyst: vanadium pentoxide [V2O5]*) - **g] Exothermic & endothermic reaction**- Reactions which proceed with - evolution or absorption of heat. - $CaO + H_2O$ → $Ca(OH)_2 + Δ$ (*heat evolved [exothermic reaction]*) - $N_2 + O_2 _3000°C_ 2NO - Δ$ (*heat absorbed [endothermic reaction]*) ### Oxides - They are binary compounds - of a metallic or non-metallic element - with oxygen. - e.g. acidic oxides [SO₂], basic oxides [CaO], amphoteric oxides [ZnO], neutral oxides ## ACTIVITIES & DEMONSTRATIONS ### Chemical Reactions **1. Pedagogy/Transactional Strategies - School Chemistry Syllabus** - Explain that chemical reactions involve - breaking of existing bonds & formation of new bonds with the absorption or release of energy (heat, light). - Explaining chemical reactions using chemical equations. - Giving examples of chemical reactions from daily life - burning of fuel, showing burning of a Mg ribbon. - Explaining the different types of reactions. - **Synthesis:** $CaO+H_2O→ Ca(OH)_2$, $C+O_2→CO_2$. - **Decomposition:** Decomposition of $CaCO_3$. - **Displacement:** Displacement of Cu from $CuSO_4$ by Zn. - **Double displacement:** Both the ions are displaced - $NaCl + AgNO_3$. - Asking children to arrange metals - Cu, Ag, Al, Mg, Fe in decreasing order of their reactivity by consulting the table of reactivity series. - Conducting experiments for different metals with metal salt solution. - Demonstrating through activity - neutralization of an acid with a base as an exothermic reaction. - Dissolving $NH_4Cl$ in water is an endothermic process. - Heating metal carbonates, nitrates, sulphates yield oxides & carbon dioxides. - Oxides are also formed by heating element in presence of air. - Activity-1 Heating limestone strongly over the flame - CaO is formed. - Activity-2: Heating Lead carbonate strongly - PbO is formed. - Dissolving an oxide - in water and testing the acidic, basic and neutral oxide with litmus paper. **2. Suggested Learning Resources** - Magnesium wire, match box. - Limestone, tongs, test tube, burner. CuO, ZnO, Al2O3, litmus paper. **3. Discussions - By the Teacher** - Students to be made aware of – i] different types of chemical reactions - ii) decomposition reactions forming oxides - by demonstrating them experimentally ## Displacement reactions | Zinc | + | Copper [II] sulphate | → | Zinc sulphate | + | Copper | |---|---|---|---|---|---|---| | Zn | + | CuSO4 | → | ZnSO4 | + | Cu | ## Double decomposition reaction | Sodium chloride | + | Silver nitrate | → | Sodium nitrate | + | Silver chloride | |---|---|---|---|---|---|---| | NaCl | + | AgNO3 | → | NaNO3 | + | AgCl [precipitate] | ## Exothermic reaction | NaOH | + | HCl | → | NaCl | + | H₂O | |---|---|---|---|---|---|---| | NaOH | + | HCl | → | NaCl | + | H₂O | ## Endothermic reaction | Ammonium chloride | + | Water | → | | | | |---|---|---|---|---|---|---| | NH4Cl | + | Water | → | | | | ## EXERCISE **Introduction** 1. State what is a chemical reaction. A chemical reaction is often accompanied by external indications or characteristics, which include: - Colour change - Evolution or absorption of heat - Evolution or absorption of heat - Formation of a precipitate 2. With reference to each of the above indications, state the external indication seen during the reaction: - i) Addition of dilute acid to an active metal - ii) Addition of dilute hydrochloric acid to silver nitrate - iii) Addition of water to quicklime - iv) Thermal decomposition of mercury (II) oxide. **Main reactions** 3. State why a direct combination reaction is called a 'synthesis reaction'. 4. Differentiate between: - a) Direct combination reaction & a decomposition reaction - b) Displacement reaction & a neutralization reaction - c) Double decomposition reaction & a displacement reaction. **Types of reactions** 5. Give balanced equations for: - i) A combination reaction involving two elements: Lime [calcium carbonate] + Heat - ii) A decomposition reaction involving a metal above hydrogen in the activity series: Copper [II] sulphate solution - iii) A thermal decomposition reaction involving a neutral oxide: Mercury [II] oxide - iv) A double decomposition reaction involving a metal salt with a sodium salt: Silver nitrate + Sodium chloride - v) A displacement reaction involving a metal salt with a sodium salt: Silver nitrate + Sodium chloride - vi) A displacement reaction involving a metal salt with a sodium salt: Silver nitrate + Sodium chloride - vii) A double decomposition neutralization reaction involving an acid & a base. - viii) A white precipitate obtained during a double decomposition reaction involving a silver salt with a sodium salt. 6. State what is meant by 'reversible' in certain chemical reactions. 7. Explain what a catalyst is used in certain chemical reactions. Give a balanced equation for a reversible catalytic reaction involving: - i) Nitrogen as one of the reactants - ii) Sulphur dioxide as one of the reactants. 8. State which type of chemical reactions proceed with evolution of heat or absorption of heat energy. State in each of the following reactions whether heat is evolved or absorbed: - i) Water is added to quicklime. - ii) Two neutral gases on passage through electric arc give nitric oxide - iii) Two neutral gases combine to give - a basic gas. 9. Certain thermal decomposition reactions result in formation of a metallic oxide. Give balanced equations for the thermal decomposition of the following which result in formation of a metallic oxide: - a) Limestone - b) Lead carbonate - c) Calcium nitrate - d) Calcium hydroxide. **Oxides** 10. State the meaning of the term 'oxide'. Give a balanced equation for formation of the following oxides: - a) Sulphur dioxide from a non-metal - b) Zinc oxide from a metal - c) Lead oxide from a mixed oxide. 11. Give two examples each of the following oxides - a) Acidic oxides b) Basic oxides c) Amphoteric oxides d) Neutral oxides. State which of the following oxides i.e. a] to d]: - i) React with water to give a base - ii) React with a base to give salt & water - iii) React with acids & bases to give salt & water. 12. Give one example each of- a) A peroxide b) A mixed oxide c) A dioxide. ## OBJECTIVE TYPE QUESTIONS **Q.1** Select the correct answer from A, B, C, D and E for each statement given below: - A: Iron - B: Carbonic acid - C: Hydrogen - D: Oxygen - E: Carbon monoxide - 1. The product formed during direct combination reaction of carbon dioxide & water. - 2. The neutral gas obtained on thermal decomposition of potassium nitrate. - 3. The displaced product of the displacement reaction of sodium with cold water. - 4. The catalyst used in the catalytic reaction involving the reactants nitrogen & hydrogen. - 5. A neutral oxide which does not react with an acid or a base to give salt & water. **Q.2** Complete the statements by filling in the blank with the correct word/s: - 1. Direct combination reaction of phosphorus pentoxide with water give [H3PO3/H₃PO₄] - 2. Decomposition of silver salts in the presence of sunlight is an example of [double decomposition/photochemical decomposition). - 3. The element molybdenum used in the reaction of nitrogen with hydrogen at elevated temperatures is an example of a [promoter/catalyst]. - 4. The reaction of coke with steam to give water gas is an example of an [exothermic/endothermic] reaction. - 5. The metal which reacts with steam and the reaction is reversible is [calcium/iron] **Q.3** Give a balanced equation for each of the following types of reactions: - 1. A thermal decomposition reaction in which a compound decomposes to give two new compounds. - 2. A reaction of direct combination i.e. synthesis in which two gases combine to give another gas. - 3. A thermal decomposition reaction in which a metallic nitrate decomposes to give- a basic oxide. - 4. A catalytic, reversible, exothermic reaction. - 5. A displacement reaction in which a metal above hydrogen in the reactivity series, displaces another metal from the solution of its compound

Chemical Reactions PDF

Document Details

Tags

Related

Summary

Full Transcript

Upgrade to continue