JEE doubts
500 doubts found
What is the difference between group and period?
A group is a vertical column (same valence electrons, similar properties); a period is a horizontal row (same number of shells).
What is the difference between catalyst on rate and catalyst on equilibrium?
A catalyst speeds a reaction by lowering activation energy but does NOT shift the equilibrium position.
When do I use E_cell = E_cathode − E_anode in Electrochemistry, and what does it mean?
standard cell EMF from electrode potentials.
What is the difference between SN1 reaction and SN2 reaction?
SN1 goes through a carbocation in two steps (favoured by 3° substrates); SN2 is a one-step backside attack (favoured by 1° substrates).
What are the most common mistakes students make in Hydrocarbons?
H adds to the carbon with more hydrogens — unless peroxides are present, which reverse it (anti-Markovnikov).
When do I use n = mass / molar mass in Some Basic Concepts (Mole Concept), and what does it mean?
number of moles from a given mass.
When do I use E_n = −13.6 Z²/n² eV in Structure of Atom, and what does it mean?
energy of an electron in a hydrogen-like atom.
What is the difference between sigma bond and pi bond?
A sigma bond forms by head-on overlap and is strong; a pi bond forms by sideways overlap of p-orbitals and is weaker.
When do I use ΔG = ΔH − TΔS in Chemical Thermodynamics, and what does it mean?
Gibbs free energy change deciding spontaneity.
When do I use pH = −log[H⁺] in Equilibrium, and what does it mean?
acidity of a solution.
How is Periodic Table & Periodicity tested in JEE, and what should I focus on?
Prioritise the core ideas: Atomic radius trend, Ionization energy, Electronegativity.
When do I use k = A·e^(−Ea/RT) in Chemical Kinetics, and what does it mean?
Arrhenius equation linking rate constant to temperature.
When do I use ΔG = −nFE in Electrochemistry, and what does it mean?
free energy change from cell potential.
How is Organic Chemistry — Basic Concepts tested in JEE, and what should I focus on?
Prioritise the core ideas: Inductive effect, Resonance, Electrophiles and nucleophiles.
How do I revise Hydrocarbons quickly before the exam?
One-page summary of Saturation, Markovnikov's rule, Aromaticity, then timed previous-year questions.
When do I use Molarity = moles / volume(L) in Some Basic Concepts (Mole Concept), and what does it mean?
concentration of a solution.
How is Structure of Atom tested in JEE, and what should I focus on?
Prioritise the core ideas: Quantum numbers, Orbitals, Filling rules.
What is the difference between polar molecule and non-polar molecule?
A polar molecule has a net dipole (water); a non-polar one has none because its dipoles cancel (CO₂).
When do I use ΔH = ΔU + Δn_gRT in Chemical Thermodynamics, and what does it mean?
relating enthalpy and internal energy changes.
When do I use K_w = [H⁺][OH⁻] = 10⁻¹⁴ in Equilibrium, and what does it mean?
the ion-product of water at 25°C.
What are the most common mistakes students make in Periodic Table & Periodicity?
it DECREASES left-to-right as nuclear charge pulls electrons closer.
When do I use t½ = 0.693/k in Chemical Kinetics, and what does it mean?
half-life of a first-order reaction.
How is Electrochemistry tested in JEE, and what should I focus on?
Prioritise the core ideas: Types of cells, Anode and cathode, Electrode potential.
What are the most common mistakes students make in Organic Chemistry — Basic Concepts?
they don't flip back and forth — the molecule is one stable resonance hybrid.