Combustion reactions: reaction when a substance reacts rapidly with a gas producing heat and light, for eg., burning a substance in the presence of air.
Exothermic reaction: is a reaction which releases heat to the surrounding. As heat is released, the temperature of the surrounding increases. Cooling a substance, freezing, condensation are examples of exothermic processes.
Endothermic reaction: is a reaction which absorbs heat from the surrounding. As heat is absorbed, the temperature of the surrounding decreases. Decomposition reactions like electrolysis of water, heating a substance, melting, vaporization and sublimation are examples of
endothermic processes.
Law of Conservation of matter: Matter can never be created or destroyed. It follows that in a chemical reaction mass and atoms are conserved. As a chemical reaction involves a rearrangement of atoms number of molecules is not conserved.
A chemical equation can be read in terms of atoms, molecules or moles.
Know that equations representing reactions of ionic compounds cannot be read in molecules. Ionic compounds are not made up of molecules, they are made up of ions.
Equations with fractional coefficients cannot be read in terms of molecules.
The number preceding the chemical symbol and indicating the quantity of particles is called coefficient.
The number used after a chemical symbol to indicate the number of atoms present per molecule is called the subscript.
Balancing chemical equations
Standard temperature and pressure (STP): 0⁰C and 1.00 atm pressure
At STP 1.00 mole of ANY gas occupies 22.4 dm3.
Write the volume ratio at STP conditions for a given reaction equation.
Know that air is 20% oxygen gas by volume therefore volume of air= 5𝑉𝑂2.
Solve problems using the volume ratio.
Write an equation including the energy required or released.
Solve problems to .determine the energy released or required.
Solve stoichiometric calculation questions using the most convenient ratio.
Limiting reagent: is the chemical which gets used up completely. It determines how much of the other reactants will be consumed and how much of the products will be produced in a chemical reaction.
Know how to determine the mass of the excess reagent left in excess
