DSE Chem Definition List ｜化學科必背definition
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Chapter 1: Planet Earth
Mixture consists of two or more pure substances which have not chemically combined together
Element is a pure substance that cannot be broken down into anything simpler by chemical methods
Compound is a pure substance made up of two or more elements chemically combined together
Saturated solution is a solution which the solvent has dissolved the maximum amount of solute it can at a specific temperature
Chapter 2: Microscopic World I
Atom is the smallest part of an element which has the chemical properties of that element.
Isotopes are different atoms of the element with same number of protons but different number of neutrons
Relative atomic mass is the weighted average of the relative isotopic masses of all of its naturally occurring isotopes of the 12C = 12.00 scale
Metallic bond is the strong, non-directional electrostatic attraction between the delocalized electrons and metal ions
Ionic bond is a strong, non-directional electrostatic attraction between oppositely charged ion. It is formed by the transfer of one or more electrons from one atom to another
Covalent bond is the strong directional electrostatic attraction between the shared electrons and the two nuclei of the bonded atoms. It is formed by sharing of outermost shell electrons between two atoms
Molecules is the smallest part of an element or a compound which can exist on its own under room conditions
Dative covalent bond is a covalent bond formed between two atoms where both electrons of the shared pair are contributed by the same atom
Chapter 3: Metals
Displacement reaction is a reaction in which a more reactive metal displaces a less reactive metal from its salt solution.
Empirical formula is a formula that shows the simplest ratio of different types of atoms in a compound.
Molecular formula is a formula that shows the actual number of each type of atom in a molecule.
Chapter 4: Acids and Bases
Acid is a molecular compound which forms H + (aq) as the only cation when dissolved in water
Base is a compound which reacts with an acid forming salt and water only
Alkali is a base which is soluble in water
Strong acid is an acid which ionizes completely in water
Weak acid is an acid which ionizes slightly in water
Standard solution is a solution with accurately known concentration
Primary standard is a substance which can be used to prepare a standard solution directly. It can be weighed out accurately and used to prepare a solution of accurate concentration.
Chapter 5: Fossil Fuels and Carbon Compounds
Hydrocarbon is compound made of hydrogen and carbon only
Petroleum is formed from the remains of marine organisms (coal: remains of ancient plants) that are buried underneath sedimentary rock and subjected to intense heat and pressure for a long time
Unsaturated compound is a compound that contains at least one carbon-carbon multiple bonds
Cracking is the breaking down of large molecules into smaller ones
Addition polymerization is a process that monomer molecules join together repeatedly to form polymer molecules without the elimination of small molecules
Chapter 6: Microscopic World II
Electronegativity is a power of the atom to attract electrons to itself in a bonding situation
Polar bond is a covalent bond is polar when the bonding electrons are not equally shared between the bonded atoms. This results when two bonded atoms have different electronegativities.
Hydrogen bond is a strong electrostatic attraction between a hydrogen atom in an O-H, N-H, or F-H bond and a lone pair of electrons on a highly electronegative atom (O, N, or F) in another molecule.
Chapter 7: Redox Reactions, Chemical Cells, and Electrolysis
Primary cells are not rechargeable while secondary cells are rechargeable.
Chemical cell converts chemical energy into electrical energy
Electrolytic cell converts electrical energy into chemical energy
Electrolyte is a substance which conducts electricity in molten / aqueous state
Chapter 8: Chemical Reactions and Energetics
For exothermic reactions, energy absorbed in breaking bonds in reactants (if any) is smaller than the energy released in forming bonds in products
Enthalpy change is the heat change of a system at constant pressure.
Standard enthalpy change of combustion is the enthalpy change when 1 mole of substance is burnt in air completely under standard conditions.
Standard conditions include:
Temperature at 298 K
Pressure at 1 atm
Substances are in their standard states
Standard enthalpy change of neutralization is the enthalpy change when one mole of water is produced from the neutralization between an acid and an alkali under standard conditions.
Standard enthalpy change of formation is the enthalpy change when one mole of the substance forms from its constituent elements in their standard states under standard conditions.
Hess’s Law states that the total enthalpy change of a chemical reaction depends on the initial and final states of the reaction, but is independent of the route taken.
Chapter 9: Rate of Reaction
Initial rate is the instantaneous rate at time = 0
Catalyst is a substance which can change (usually increase) the rate of a reaction but itself remains chemically unchanged at the end of reaction.
Effective collisions: Reactant particles must have sufficient energy to react and collide in a proper orientation in order for a reaction to occur.
Chapter 10: Chemical Equilibrium
Characteristics of dynamic equilibrium:
Both reactants and products are present and their concentrations remain unchanged.
he rate of forward reaction is equal to the rate of backward reaction.
Equilibrium can be reached from either direction of a reversible reaction.
Equilibrium can only be reached in a closed system.
Le Châtelier’s Principle states that when a chemical system at equilibrium is disturbed by a change in conditions, the equilibrium position will shift in a direction that tends to counteract the change.
Chapter 11: Chemistry of Carbon Compounds
Functional group is a specific atom or group of atoms responsible for the characteristic properties of a compound.
Isomers are different compounds that have the same molecular formula.
Stereoisomers are isomers in which the atoms are linked in the same order but have different arrangements in space.
Cis-trans isomers (or geometrical isomers) result from the restricted rotation about the carbon-carbon double bond.
Chiral carbon is a carbon bonded to 4 different atoms or groups of atoms
A chiral molecule and its mirror image are called a pair of enantiomers (or optical isomer). They are non-superimposable
Condensation polymerization is a process that monomer molecules join together repeatedly to form polymer molecules with the elimination of small molecules (such as H2O or HCl)
Chapter 13: Industrial chemistry
Activation energy is the minimum amount of energy possessed by the colliding reactant particles required to start a reaction.
Chapter 15: Analytical chemistry
Rf value is the ratio of the distance travelled by the component from the baseline to the distance travelled by the solvent from the baseline
Different substances can be separated by chromatography as they have different solubilities in the mobile phase and have different degrees of adsorption onto the stationary phase.
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