這篇文章會囊括幾乎所有DSE Chemistry 化學要背的Definition！
Chapter 1：Planet Earth
Distillation (principle)
Water boils at about 100°C but the salts in the sea are non-volatile. The steam formed condenses on the cold surface of the condenser to give liquid water.
Chapter 2：Microscopic world I
Elements
Are substances that cannot be separated into anything simpler by chemical methods
Compounds
Are substances containing at least two types of atoms chemically bonded together
Mixtures
Contain two or more substances (can be elements or compounds) which are not chemically bonded together
Isotopes
Are atoms of the same element having the same number of protons but different number of neutrons
Relative atomic mass
Is the weighted average of relative isotopic mass of all naturally occurring isotopes on carbon-12 scale
Groups
are columns in the periodic table, and the elements in the same group have the same number of electrons in the outermost shell
Periods
are rows in the periodic table, and the elements in the same period have the same number of occupied electron shells
Octet rule
Strong tendency of atoms to attain 8 outermost shell electrons.
Ionic bond
Electrostatic attraction between oppositely charged ions
Covalent bond
Electrostatic attraction between the bonding electrons and the nuclei of the bonding atoms
Dative covalent bond
A type of covalent bond in which both electrons come from the same atom
Metallic bond
Electrostatic attraction between metal cation and the sea of delocalized electrons
Chapter 3：Metals
Ductile
Can be pulled to form wires
Malleable
Can be bent to form different shapes
Displacement reaction
A type of reaction in which a more reactive metal (halogen) replaces a less reactive one from a solution of the compound of the less reactive metal (halogen)
Empirical formula
Is a formula showing different types of atoms in a compound in their simplest ratio
Molecular formula
Is a formula showing the number of different types of atoms in a compound
Sacrificial protection
Is a process of attaching a more reactive metal to the object such that the more reactive metal will lose electron instead of the object
Galvanization/Zinc-plating
Zinc coating prevents iron from contacting water and oxygen. When coating is damaged, the electrons flow from zinc to iron to prevent iron from losing electrons.
Alloy
A mixture containing at least one metal
Electroplating
Is a process of plating a thin layer of metal on the surface of an object by electrolysis
Anodization
Is a process of thickening the oxide layer on the surface of aluminium by electrolysis
Chapter 4：Basicity
Is the number of ionizable hydrogen ions per acid molecule
Strong acid / base
Is an acid / base which completely ionizes in water
Weak acid / base
Is an acid / base which partly ionizes in water
Alkalis
Are soluble bases
Standard solution
Is a solution of accurately known concentration
End point
Is the point at which the indicator changes color / titration completes
Amphoteric
Describes substances which can react with both acids and bases
Chapter 5：Fossil fuels and carbon compounds
Fossil fuels
Coal, petroleum and natural gas
Formation of coal
Formed when large quantities of plants are buried underneath sand and mud and subjected to intense heat and pressure for a long time.
Formation of petroleum
Formed when large quantities of dead marine organisms (, such as planktons and algaes) (IM) that are buried underneath sedimentary rock and subjected to intense heat and pressure for a long time(1M).
Molecules in the same homologous series
Molecules with the same functional group and same general formula. They show gradual change in physical properties.
Substitution
A chemical reaction in which an atom (or group of atoms) is replaced by another atom (group of atoms).
Cracking
The process of breaking down large alkane molecules into smaller alkene and alkane molecules in the absence of air.
Polymer
A mixture of polymer chains with different chain lengths.
Monomer
Small molecule used to be repeatedly joined to form polymer chains.
Addition polymerization
Reaction that monomer molecules repeatedly join together to form polymer chains without the elimination of small molecules.
Chapter 6：Microscopic world II
Electronegativity
Is a measure of the ability of an atom to attract the bonding electrons
Polar bonds
Are covalent bonds formed between two atoms with different electronegativity
Polar molecules
Are molecules in which the polarities of the polar bonds are not completely cancelled
Hydrogen bond
Strong electrostatic attraction between hydrogen atom of O-H,H-F,N-H and the lone pair electrons on a highly electronegative atom (F,O,N) of another molecule.
Chapter 7：Redox reactions, chemical cells and electrolysis
Electrolytes
Are chemicals (ionic or acid solutions) that can be decomposed by electricity
Electrolysis
Is a process in which an electrolyte is decomposed by electricity
Primary cell
A cell that cannot be recharged / is non-rechargeable.
Secondary cell
A cell that can be recharged.
Cathode
An electrode that undergoes reduction / attracts cations
Anode
An electrode that undergoes oxidation / attracts anions
Oxidation
Is a process of gaining oxygen / losing electrons / losing hydrogen / increasing the oxidation number
Reduction
Is a process of losing oxygen / gaining electrons / gaining hydrogen / decreasing the oxidation number
Oxidizing agent
Is a chemical that undergoes reduction / loses oxygen / gains electrons / gains hydrogen / decreases in oxidation number
Reducing agent
Is a chemical that undergoes oxidation / gains oxygen / loses electrons / loses hydrogen / increases in oxidation number
Salt bridge
A strip of filter paper soaked in an electrolyte. It provides ions to balance the charges in the solutions of two half cells.
Porous pot
Allows ions to pass through to complete the circuit.
Chapter 8：Chemical reactions and energy
Exothermic reactions
Are reactions that release heat
Endothermic reactions
Are reactions that absorb heat
Enthalpy changes
Are heat changes under constant pressure
Standard conditions
Refer to 25°C (298K) and 1 atm (100 kPa)
Standard enthalpy change of formation
Is the enthalpy change when one mole of substance is formed from its constituent elements in standard states under standard conditions
Standard enthalpy change of combustion
Is the enthalpy change when one mole of substance (fuel) is completely burnt (in excess oxygen) under standard conditions
Standard enthalpy change of neutralization
Is the enthalpy change when one mole of water is formed from the neutralization reaction between an acid and a base under standard conditions
Hess’s law
States that the enthalpy change of a reaction is the same regardless of the path the reaction takes place
Chapter 9：Rate of reaction
Rate of reaction
Is the change in the concentration (or other physical quantities e.g., mass, volume etc.) of reactants / products over time
Initial rate
Is the instantaneous rate at the beginning of the experiment
Instantaneous reaction rate
The rate at a particular instant of reaction. Slope of tangent of concentration curve at that particular time.
Chapter 10：Chemical equilibrium
Dynamic equilibrium
Is a state in which the forward rate equals the backward rate (i.e.,
concentration of reactants and products are constant) in a reversible reaction
Le Chatelier’s principle
States that the equilibrium will shift in a way to minimize the change that causes it
Chapter 11：Chemistry of carbon compounds
Homologous series
Is a series of organic compounds with the same general formula, successive members differ by a CH2 group, similar chemical properties and gradual change in physical properties
Markovnikov's Rule
In the addition reaction / of hydrogen halide (HX) to the C=C double bond of / an alkene, the hydrogen atom in HX is added to the carbon atom with the greater number of hydrogen atoms / while the halogen atom in HX is added to the carbon atom with the smaller number of hydrogen atoms.
Structural isomers
Are compounds with the same molecular formula but different structures
Enantiomers
Are non-superimposable mirror images of each other
Chiral carbons
Are carbon atoms with four different groups attached to them
Optical isomers
Are isomers which can rotate plane polarized light in opposite direction (but same angle)
Saturated compounds
Are compounds with single bonds only
Unsaturated compounds
Are compounds with at least one double or triple bond
(Free) radicals
Are chemical species with unpaired electrons
Substitution reactions
Are reactions in which one atom (group of atoms) is replaced by another
Addition reactions
Are reactions in which a group of atoms is attached to a double bond (or triple bond) without the loss of molecules
Polymerization
Is a process in which small molecules called monomers are repeatedly joining to form a large molecule
Addition polymerization
Is a process in which small molecules called monomers are repeatedly joining to form a large molecule without the loss of molecules
Condensation polymerization
Is a process in which small molecules called monomers are repeatedly joining to form a large molecule with the loss of small molecules (e.g., water)
Esterification
Is a reversible reaction in which a carboxylic acid reacts with an alcohol to form an ester with the loss of a water molecule using acid as catalyst
Hydrolysis of ester
Is a reaction in which an ester is broken down into a carboxylic acid / carboxylate and an alcohol under acid / alkali catalysts
Hydrolysis of amide
Is a reaction in which an amide is broken down into a carboxylic acid / carboxylate and ammonia under acid / alkali catalysts
Dehydration
Is a reaction in which water molecules are removed from a compound
Catalysts
Are chemicals that increase the rate of reaction by providing an alternative pathway with lower activation energy
Activation energy
Is the minimum energy required for a reaction to start