CHEMISTRY REVISION MCQ NOTES
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Ideal Gases, (Needed to solve 9701_w22_qp_12 Q14)
- Gases that are in High temperature and Low pressure are most likely to show ideal
gas behaviors
- Molecules have to be non– polar
E.g. Nitrogen, Oxygen, Noble gases
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Enthalpy Change (ΔH) = Σ energy in products - Σ energy in reactants
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Enthalpy Change (ΔH) = Q/moles (Units: kJ/mol)
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In group 2 as you go down, solubility and reactivity increase so the alkalinity of the
elements increases
E.g. Ba(OH)₂ is a stronger base than Mg(OH)₂
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Question – What is the oxidation state of the chlorine containing species that kills
bacteria in drinking water? -(9701_w22_qp_12)
HClO is the species,
hence Oxidation state of Cl = +1
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Why does Oxygen have a lower ionization energy than Nitrogen In the basic tend even
though oxygen has more protons than nitrogen. (9701_m22_qp_22 Q1 b) ii))
Because in the 2p orbital of Nitrogen there’s 3 unpaired electrons but in the 2p orbital
of oxygen there’s one paired electron and 2 unpaired electrons, these paired electrons
in Oxygen undergo spin-pair repulsion which out-weights the increased nuclear charge
due to protons
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Al2O3 + 2NaOH  2H20 + 2NaAl(OH)4
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In Exothermic – Increasing temp. favors backward endothermic reaction so equilibrium
position shifts to the left, similarly lowering temp. favors forward reaction hence shifts
to right
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In Endothermic – Increasing temp favors forward reaction so shifts to right, decreasing
shifts to left as it favors exothermic reaction
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Increasing pressure favors side with less no.of.moles
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Decreasing pressure favors side with more no.of.moles
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Least likely to behave like a ideal gas Is when you have,
- Hydrogen bonds and when number of electron is greater
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Finding No.of Stereoisomers = 2𝑛 where N = No.of.stereogenic
Sterioginic means the atoms which can form sterioisomers e.g – chiral centers and
double bonds
(All chiral centers are stereogenic centers but all stereogenic centers are not chiral
centers.)
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Bond forming = Exothermic
Bond Breaking = Endothermic
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Note – Al, Si P chlorides give acidic solutions
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When compounds are decomposed, the lower the Mr, larger the number of moles so
greater the volume of gas , e.g. Ba(CO)3 will give less vol of gas than Mg(CO)3 as
Ba(CO)3 has greater Mr (remember n = m/mr)
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Note when nitrates decompose, NO2 AND O2 is released so more vol of gas than when
Carbonates decompose (only CO2 produced)
Remember this definition
Relative Atomic mass is the weighted mass of natural occurring atoms of an element on a scale
where a carbon-12 atom has an exact mass of 12 units
i.e – the ratio of an atom of the element to the mass of an atom of carbon 12 is 1:12 or 1/12