Short interactive lessons that ask a question before they explain. One session takes about ten minutes and ends with questions to check what you have understood.
A reaction forms new substances. A change of state, colour or temperature, or a gas given off, points to one.
Class 10 · Science Reactions, and How We Write Them FreeFrom a sentence to a word equation to formulae. A skeletal equation has correct formulae but unequal atom counts.
Class 10 · Science Reactions, and How We Write Them FreeAtoms are not created or destroyed, so each element must have equal counts on both sides. Change coefficients, never formulae.
Class 10 · Science Reactions, and How We Write Them FreeCombination forms one product from several reactants; decomposition breaks one reactant into several.
Class 10 · Science Reactions, and How We Write Them FreeAn exothermic reaction releases heat; an endothermic one takes heat in. Bond energies decide which.
Class 10 · Science Reactions, and How We Write Them FreeA more reactive metal displaces a less reactive one from a solution of its compound. The reverse does not occur.
Class 10 · Science Reactions, and How We Write Them FreeTwo ionic compounds exchange ions. If one new combination is insoluble, it separates as a precipitate.
Class 10 · Science Reactions, and How We Write Them FreeGain of oxygen is oxidation, loss is reduction, and the two occur together. Rusting and rancidity are oxidation.
Class 10 · Maths Real Numbers FreeEvery composite number is a product of primes in exactly one way, apart from order.
Class 10 · Maths Real Numbers FreeThe HCF is the shared primes at their smaller powers; the LCM is all the primes at their larger powers.
Class 10 · Maths Real Numbers FreeFor two numbers, HCF × LCM equals their product. Prime factorisations decide divisibility questions for every case at once.
Class 10 · Maths Real Numbers FreeA fraction in lowest terms terminates exactly when its denominator has no prime factors other than 2 and 5.
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