Chemistry notes form4

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Short Notes: Form 5 Chemistry
Rate or Reaction
Calculation
Rate of Reaction (Average Rate)

Rates of reaction =

Quantity change of reactants/products
Total time for the reaction

If the quantity change is immeasurable

Rates of reaction =

1
Total time for the reaction

Find the Rate From a Graph
Average Rate

Rates At an Instant

The rate of reaction is equal to the slope of the graph The rate of reaction at an instant, t, is equal to the of quantity against time. slope of tangent at that instant.

Rate of Reaction =

Δ(Product)
Δ(Time)

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Rate of Reaction =

1

Δ(Product)
Δ(Time)

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Chemical Reaction
Precipitation of Sulphur

2HCl(aq) + Na2S2O3(aq) ⎯→ 2NaCl(aq) + S(s) + SO2(g) + H2O(l)
Na2S2O3: Sodium thiosulphate

Notes:
1. Yellow precipitate (sulphur) is formed.
2. The reaction is slow.

Potassium Dichromate (VI) with Ethanedioic Acid

Cr2O72- + 14H+ + 3C2O42- ⎯→ 6CO2 + 7H2O + 2Cr3+
Notes:
1. In the reaction, the orange colour of the solution turns into green.

Cr2O72-: dichromate(VI) ion (Orange)
C2O42-: ethanedioate ion (Colourless)
Cr3+ : Chromium(III) ion (green)

Potassium Manganate(VII) with Ethanedioic Acid

2MnO4- + 16H+ + 5C2O42- ⎯→ 10CO2 + 8H2O + 2Mn2+
Notes:
1. Mn2+ is colourless
2. In the reaction, the purple colour of the solution turns into colourless.

MnO4-: Manganate(VII) ion (Purple)
Mn2+: Manganese(II) ion colourless

Decomposition of Hydrogen Peroxide

2H2O2 - ⎯→ 2H2O + O2
Catalyst: manganese(IV) oxide(MnO2), Iron(III) oxide (Fe2O3), silver (Ag)
Haber Process (Manufacture Ammonia)

N2 + 3H2 ⎯→ 2NH3
(More detail in Form 4 Chapter 9)
Contact Process(Manufacture Sulphuric Acid)

2SO2 + O2 ⎯→ 2SO3
(More detail in Form 4 Chapter 9)

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2

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Ostwald Process (Manufacture Nitric Acid)
Stage 1

4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
Notes:
1.