Grade 12 IEB Physical Science: Chemistry (Paper 2) SAG De nitions:
Section A: Quantitative Chemistry:
• Molar mass: The mass in grams of one mole of that substance
• Solution: A homologous mixture of solute and solvent
• Solute: The substance that is dissolved in the solution
• Solvent: The substance in which another substance is dissolved, forming a solution
• Concentration: The amount of solute per unit volume of solution
• Yield: A measure of the extent of a reaction, generally measured by comparing the amount of
product against the amount of product that is possible
Section B: Chemical Bonding:
• Covalent bond: A sharing of at least one pair of electrons by two non-metal atoms
• Non-polar covalent bond (Pure covalent): An equal sharing of electrons
• Polar covalent bond: An unequal sharing of electrons leading to a dipole forming (as a result of
electronegativity di erence)
• Electronegativity: A measure of the tendency of an atom to attract a bonding pair of electrons
• Ionic bond: A transfer of electrons and subsequent electrostatic attraction
• Metallic bonding: Between a positive kernel and a sea of delocalised electrons
• Intermolecular forces: A weak force of attraction between molecules, ions or atoms of noble
gases
Section C: Energy Change & Rates of Reactions:
• Heat of reaction: The net change of chemical potential energy of the system
• Exothermic reactions: Reactions which transform chemical potential energy into thermal energy
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, • Endothermic reactions: Reactions which transform thermal energy into chemical potential energy
• Activation energy: The minimum energy required to start a chemical reaction OR The energy
required to form the activated complex
• Activated complex: A high energy, unstable, temporary transition state between the reactants and
the products
• Reaction rate: The change in concentration per unit time of either a reactant or product
• Catalyst: A substance that increases the rate of reaction but remains unchanged at the end of the
reaction
Section D: Chemical Equilibrium:
• Closed system: one in which mass is conserved inside the system but energy can enter or leave
the system freely
• Open system: one in which both energy and matter can be exchanged between the system and
its surroundings
• Reversible reaction: Reaction in which products can be converted back into reactants
• Le Châtelier's principle: When an external stress (change in pressure, temperature or
concentration) is applied to a system in dynamic chemical equilibrium, the equilibrium point will
change in such a way as to counteract the stress
Section E: Acids & Bases:
• Acid: A proton donor
• Base: A proton acceptor
• ionisation: The reaction of a molecular substance with water to produce ions
• Strong acid: An acid that ionises completely in an aqueous solution
• Weak acid: Acid that only ionises partially in an aqueous solution
Section A: Quantitative Chemistry:
• Molar mass: The mass in grams of one mole of that substance
• Solution: A homologous mixture of solute and solvent
• Solute: The substance that is dissolved in the solution
• Solvent: The substance in which another substance is dissolved, forming a solution
• Concentration: The amount of solute per unit volume of solution
• Yield: A measure of the extent of a reaction, generally measured by comparing the amount of
product against the amount of product that is possible
Section B: Chemical Bonding:
• Covalent bond: A sharing of at least one pair of electrons by two non-metal atoms
• Non-polar covalent bond (Pure covalent): An equal sharing of electrons
• Polar covalent bond: An unequal sharing of electrons leading to a dipole forming (as a result of
electronegativity di erence)
• Electronegativity: A measure of the tendency of an atom to attract a bonding pair of electrons
• Ionic bond: A transfer of electrons and subsequent electrostatic attraction
• Metallic bonding: Between a positive kernel and a sea of delocalised electrons
• Intermolecular forces: A weak force of attraction between molecules, ions or atoms of noble
gases
Section C: Energy Change & Rates of Reactions:
• Heat of reaction: The net change of chemical potential energy of the system
• Exothermic reactions: Reactions which transform chemical potential energy into thermal energy
fi
, • Endothermic reactions: Reactions which transform thermal energy into chemical potential energy
• Activation energy: The minimum energy required to start a chemical reaction OR The energy
required to form the activated complex
• Activated complex: A high energy, unstable, temporary transition state between the reactants and
the products
• Reaction rate: The change in concentration per unit time of either a reactant or product
• Catalyst: A substance that increases the rate of reaction but remains unchanged at the end of the
reaction
Section D: Chemical Equilibrium:
• Closed system: one in which mass is conserved inside the system but energy can enter or leave
the system freely
• Open system: one in which both energy and matter can be exchanged between the system and
its surroundings
• Reversible reaction: Reaction in which products can be converted back into reactants
• Le Châtelier's principle: When an external stress (change in pressure, temperature or
concentration) is applied to a system in dynamic chemical equilibrium, the equilibrium point will
change in such a way as to counteract the stress
Section E: Acids & Bases:
• Acid: A proton donor
• Base: A proton acceptor
• ionisation: The reaction of a molecular substance with water to produce ions
• Strong acid: An acid that ionises completely in an aqueous solution
• Weak acid: Acid that only ionises partially in an aqueous solution
