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800 most-asked Class 11 & 12 (+1 / +2) questions across Physics, Chemistry, Maths and Biology — each with a model answer and the exact marking-scheme points examiners reward. Revise smart, walk in calm.
ChemistryClass 113 marksmedium
Thermodynamics
When 1 kJ of heat is supplied to a gas, it does 200 J of work by expanding. Calculate the change in internal energy of the gas.
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Heat supplied to the system q = +1 kJ = +1000 J. Work is done BY the gas, so work done on the system w = -200 J. By the first law, delta U = q + w = 1000 + (-200) = 800 J. The internal energy increases by 800 J.
delta U = q + w
Marking-scheme points
- ✓q = +1000 J (heat absorbed)
- ✓Work done by gas -> w = -200 J
- ✓delta U = q + w = 1000 - 200 = 800 J
ChemistryClass 113 markshard
Thermodynamics
Given: C(s) + O2(g) -> CO2(g), delta H = -393.5 kJ and CO(g) + 1/2 O2(g) -> CO2(g), delta H = -283.0 kJ. Calculate the enthalpy of formation of CO(g).
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We want C(s) + 1/2 O2(g) -> CO(g). By Hess's law, subtract the second equation from the first: delta H(reqd) = delta H1 - delta H2 = (-393.5) - (-283.0) = -110.5 kJ. So the enthalpy of formation of CO is -110.5 kJ/mol.
delta H(reqd) = delta H1 - delta H2
Marking-scheme points
- ✓Target: C + 1/2 O2 -> CO
- ✓Subtract equation 2 from equation 1
- ✓delta H = -393.5 - (-283.0) = -110.5 kJ/mol
ChemistryClass 113 marksmedium
Thermodynamics
Write the Gibbs-Helmholtz equation and state the criteria of spontaneity in terms of delta G.
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The Gibbs energy change is given by delta G = delta H - T delta S. Criteria of spontaneity: if delta G < 0 (negative), the process is spontaneous; if delta G = 0, the system is at equilibrium; if delta G > 0 (positive), the process is non-spontaneous (the reverse is spontaneous). A reaction is always spontaneous when delta H is negative and delta S is positive.
delta G = delta H - T delta S
Marking-scheme points
- ✓delta G = delta H - T delta S
- ✓delta G < 0: spontaneous; = 0: equilibrium; > 0: non-spontaneous
- ✓delta H negative and delta S positive -> always spontaneous
ChemistryClass 113 markshard
Thermodynamics
For a reaction, delta H = -92.4 kJ and delta S = -198 J/K at 298 K. Calculate delta G and predict whether the reaction is spontaneous.
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Equilibrium
For the reaction N2(g) + 3H2(g) <=> 2NH3(g), write the expression for Kc and state the relation between Kp and Kc.
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Equilibrium
For the equilibrium N2O4(g) <=> 2NO2(g), the equilibrium concentrations are [N2O4] = 0.02 mol/L and [NO2] = 0.04 mol/L. Calculate Kc.
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Equilibrium
What is the effect of temperature and of a catalyst on a system at equilibrium?
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Equilibrium
Calculate the pH of a 0.01 M NaOH solution at 298 K.
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Equilibrium
What is a buffer solution? Give one example of an acidic buffer and write the Henderson-Hasselbalch equation.
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Equilibrium
The solubility product (Ksp) of AgCl is 1.8 x 10^-10 at 298 K. Calculate its solubility in mol/L.
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Redox Reactions
Balance the following redox reaction in acidic medium by the ion-electron (half-reaction) method: MnO4- + Fe2+ -> Mn2+ + Fe3+.
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Hydrogen
What is hard water? Distinguish between temporary and permanent hardness and give one method to remove each.
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The s-Block Elements
Describe the trend in solubility of the hydroxides and sulphates of alkaline earth metals down the group. Give the flame colours of Ca, Sr and Ba.
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The p-Block Elements
Describe the structure and bonding in diborane (B2H6).
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Organic Chemistry: Some Basic Principles and Techniques
What is structural isomerism? Name and briefly explain any three types.
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Organic Chemistry: Some Basic Principles and Techniques
What is hyperconjugation? How does it explain the stability of carbocations?
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Organic Chemistry: Some Basic Principles and Techniques
Briefly describe crystallisation, simple distillation and steam distillation as methods of purifying organic compounds.
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Hydrocarbons
How is ethene prepared by dehydration of ethanol? How can you test for unsaturation in an alkene?
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Hydrocarbons
State Huckel's rule of aromaticity. Why is benzene aromatic?
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Hydrocarbons
How would you chemically distinguish between ethane, ethene and ethyne?
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