Chemical Reactions and Equations : All Equations

Part of: Class 10 Science Notes - Chemical Reactions and Equations

1. Burning of Magnesium Ribbon

$2\text{Mg}(s)+{\text{O}}_2(g)⟶2\text{MgO}(s)+\text{Heat}$

Equation Description: Magnesium metal reacts with atmospheric oxygen when heated to produce magnesium oxide ash and thermal energy.

• $\text{Mg}$ is burnt in air.
• Goes into a vigorous exothermic reaction with oxygen to form $\text{MgO}$.
• $\text{MgO}$ is a white powder.
• Is a combination reaction.

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2. Quicklime in Water

$\text{CaO}(s)+{\text{H}}_2\text{O}⟶{\text{Ca(OH)}}_2(aq)+\text{Heat}$

Equation Description: Calcium oxide (quicklime) reacts vigorously with water to form a solution of calcium hydroxide (slaked lime), releasing significant heat.

• Exothermic & Combination Reaction.
• $\text{Ca}$ is 3rd on reactivity series, thus this reaction is extremely violent.
• $\text{CaO}$ is Quicklime ("Chuna" in Hindi); is used in cement making.
• Product ${\text{Ca(OH)}}_2$ is Slaked lime used in white washing.

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3. White Washing Walls

${\text{Ca(OH)}}_2(aq)+{\text{CO}}_2(g)⟶{\text{CaCO}}_3(s)+{\text{H}}_2\text{O}(l)$

Equation Description: Aqueous calcium hydroxide reacts with carbon dioxide from the air to form a solid layer of calcium carbonate and water.

• Slaked lime is used for white washing walls.
• Slaked lime slowly reacts with ${\text{CO}}_2$ present in air which produces ${\text{CaCO}}_3$ (A thick milky layer on walls which gives them their shiny look).
• ${\text{CaCO}}_3$ is also the chemical formula for marble.
• Is a combination reaction.

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4. Decomposition of Limestone

${\text{CaCO}}_3(s)\stackrel{\Delta }{\to }\text{CaO}(s)+{\text{CO}}_2(g)$

Equation Description: Solid calcium carbonate (limestone) breaks down into calcium oxide and carbon dioxide gas when subjected to high heat.

(Limestone $\to$ Quicklime + Carbon Dioxide)

• Is a thermal decomposition reaction.
• Used in various industries as Quicklime has many uses (e.g., Producing Cement).

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5. Ferrous Sulphate & Heat (Important Reaction)

Step 1: ${\text{FeSO}}_4\cdot 7{\text{H}}_2\text{O}\stackrel{\Delta }{\to }{\text{FeSO}}_4+7{\text{H}}_2\text{O}$ (evaporates later)
Step 2: $2{\text{FeSO}}_4(s)\stackrel{\Delta }{\to }{\text{Fe}}_2{\text{O}}_3(s)+{\text{SO}}_2(g)+{\text{SO}}_3(g)$

Equation Description: Hydrated ferrous sulphate first loses its water of crystallization, then the anhydrous salt decomposes into ferric oxide and sulfur oxide gases.

• Thermal decomposition.
• ${\text{SO}}_2$ / ${\text{SO}}_3$: Acidic, Pollutant.

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6. Lead Nitrate & Thermal Decomposition

$2{\text{Pb(NO}}_3{)}_2(s)\stackrel{\Delta }{\to }2\text{PbO}(s)+4{\text{NO}}_2(g)+{\text{O}}_2(g)$

Equation Description: Lead nitrate powder decomposes upon heating to form lead oxide, reddish-brown nitrogen dioxide gas, and oxygen.

• Thermal Decomposition & Endothermic.
• Observations:
• Brown fumes of ${\text{NO}}_2$.
• Yellowish Remnant.
• Cracking sound.

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7. Electrolysis

$2{\text{H}}_2\text{O}(l)\stackrel{\text{Electric}}{\to }2{\text{H}}_2(g)+{\text{O}}_2(g)$

Equation Description: Liquid water is broken down into its constituent elements, hydrogen and oxygen gases, through the application of an electric current.

• Connected to Positive terminal = Anode $\to$ ${\text{O}}_2$ obtained.
• Connected to Negative terminal = Cathode $\to$ ${\text{H}}_2$ obtained.
• ${\text{H}}_2$ produces pop sound on burning candle & extinguishes candle.
• ${\text{O}}_2$ makes candle burn brighter as it is a supporter of combustion.
• Note: As Pure water is a poor conductor of electricity, we cannot use pure water in electrolysis.

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8. Photochemical Decomposition of Silver Compounds

$2\text{AgCl}(s)\stackrel{\text{Sunlight}}{\to }2\text{Ag}(s)+{\text{Cl}}_2(g)$

Equation Description: Silver chloride and silver bromide undergo decomposition when exposed to sunlight, separating into metallic silver and halogen gases.

(White $\to$ Grey + Yellowish Green)

$2\text{AgBr}(s)\stackrel{\text{Sunlight}}{\to }2\text{Ag}(s)+{\text{Br}}_2(g)$

• $\text{AgCl}$ & $\text{AgBr}$ are used in Black & White Photography.

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9. Displacement Reactions

• $\text{Zn}(s)+{\text{CuSO}}_4(aq)⟶{\text{ZnSO}}_4(aq)+\text{Cu}(s)$
• $\text{Pb}(s)+{\text{CuCl}}_2(aq)⟶{\text{PbCl}}_2(aq)+\text{Cu}(s)$

Equation Description: A more reactive metal (Zinc or Lead) replaces a less reactive metal (Copper) from its salt solution.

• $\text{Zn}$ and $\text{Pb}$ are more reactive than $\text{Cu}$.
• Thus they displace $\text{Cu}$ from its compound.

8. Displacement Reaction of ${\text{CuSO}}_4$ with Iron

$\text{Fe}(s)+{\text{CuSO}}_4(aq)⟶{\text{FeSO}}_4(aq)+\text{Cu}(s)$

(Blue $\to$ Pale Green + Reddish Brown)

Equation Description: Iron metal reacts with blue copper sulphate solution to form green iron sulphate and a reddish-brown copper deposit.

• Iron nail in ${\text{CuSO}}_4$ solution.
• Iron nail becomes brownish due to copper deposit.
• Solution becomes Pale green due to ${\text{FeSO}}_4$.