Terms and Definitions (Grade 12 NSC Matric Physical Sciences): Revision Notes

Terms and Definitions

This comprehensive revision note contains all the essential terms and definitions you need to know for Grade 12 Physical Sciences. The document is organised into two main sections: Physics (Paper 1) and Chemistry (Paper 2). Each definition is presented exactly as it appears in the official curriculum to ensure accuracy and consistency with exam requirements.

Physics (Paper 1)

Physics forms the first paper of your Physical Sciences examination. The following sections cover all the key concepts and their precise definitions.

Newton's laws and application of Newton's laws

Understanding forces is fundamental to physics. Here are the key force-related definitions you must know:

Normal force (N): The force or the component of a force which a surface exerts on an object with which it is in contact, and which is perpendicular to the surface.

Frictional force (f): The force that opposes the motion of an object and which acts parallel to the surface.

Static frictional force (fs): The force that opposes the tendency of motion of a stationary object relative to a surface.

kinetic frictional force(fk): The force that opposes the motion of a moving object relative to a surface.

Newton's three laws of motion

Newton's first law of motion: A body will remain in its state of rest or motion at constant velocity unless a non-zero resultant/net force acts on it.

Newton's second law of motion: When a resultant/net force acts on an object, the object will accelerate in the direction of the force at an acceleration directly proportional to the force and inversely proportional to the mass of the object.

Newton's third law of motion: When object A exerts a force on object B, object B SIMULTANEOUSLY exerts an oppositely directed force of equal magnitude on object A.

Newton's law of universal gravitation

Gravity is a fundamental force that affects all objects with mass:

Newton's Law of Universal Gravitation: Each body in the universe attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Weight: The gravitational force, in newton (N), exerted on an object.

Mass: The amount of matter in a body measured in kilogram (kg).

Weightlessness: The sensation experienced when all contact forces are removed i.e. no external objects touch one's body.

Momentum and impulse

Momentum is a key concept in understanding collisions and interactions between objects:

Momentum: The product of an object's mass and its velocity.

Newton's second law of motion in terms of momentum: The resultant/net force acting on an object is equal to the rate of change of momentum of the object in the direction of the resultant/net force.

Impulse: The product of the resultant/net force acting on an object and the time the resultant/net force acts on the object.

Closed/Isolated system (in Physics): A system on which the resultant/net external force is zero.

Vertical projectile motion in one dimension (1D)

Projectile motion describes objects moving under the influence of gravity alone:

A projectile: An object upon which the only force acting is the force of gravity.

Work, energy and power

Energy transformations are central to understanding physical processes:

The work done on an object by a constant force F: The work done on an object by a constant force F where $F \Delta x \cos \theta$, $F$ is the magnitude of the force, $\Delta x$ the magnitude of the displacement and $\theta$ the angle between the force and the displacement

The work-energy theorem: The net/total work done on an object is equal to the change in the object's kinetic energy OR the work done on an object by a resultant/net force is equal to the change in the object's kinetic energy.

Conservative force: A force for which the work done in moving an object between two points is independent of the path taken.

Non-conservative force: A force for which the work done in moving an object between two points depends on the path taken.

Power: The rate at which work is done or energy is expended.

Doppler effect

The Doppler effect explains changes in wave frequency due to relative motion:

Doppler effect: The change in frequency (or pitch) of the sound detected by a listener because the sound source and the listener have different velocities relative to the medium of sound propagation.

Electrostatics

Electrostatics deals with stationary electric charges and the forces between them:

Coulomb's law: The magnitude of the electrostatic force exerted by one point charge ($Q_1$) on another point charge ($Q_2$) is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance ($r$) between them

Electric field: A region of space in which an electric charge experiences a force.

Electric field at a point: The electric field at a point is the electrostatic force experienced per unit positive charge placed at that point.

Electric circuits

Understanding electric circuits is essential for practical applications of electricity:

Ohm's law: The potential difference across a conductor is directly proportional to the current in the conductor at constant temperature.

Power: The rate at which work is done.

Internal resistance: The resistance between the terminals of a real battery.

Electrodynamics

Electrodynamics involves alternating current and its properties:

rms for an alternating voltage or an alternating current: The rms value of AC is the DC potential difference/current which dissipates the same amount of energy as AC.

Optical phenomena and properties of materials

Light interacts with matter in fascinating ways, leading to various optical phenomena:

Photoelectric effect: The process whereby electrons are ejected from a metal surface when light of suitable frequency is incident on that surface.

Threshold frequency ($f_0$): The minimum frequency of light needed to emit electrons from a certain metal surface.

Work function ($W_0$): The minimum energy that an electron in the metal needs to be emitted from the metal surface.

Atomic absorption spectrum: An atomic absorption spectrum is formed when certain frequencies of electromagnetic radiation passes through a medium, e.g. a cold gas, is absorbed.

Atomic emission spectrum: An atomic emission spectrum is formed when certain frequencies of electromagnetic radiation are emitted due to an atom's electrons making a transition from a high-energy state to a lower energy state.

Chemistry (Paper 2)

Chemistry forms the second paper of your Physical Sciences examination. The following sections cover all the key chemical concepts and their precise definitions.

Representing chemical change

Chemical changes involve transformations of matter, and understanding these requires knowledge of key terms:

Molar volume of gases: 1 mole of any gas occupies 22,4 dm³ at 0 °C (273 K) and 1 atmosphere (101,3 kPa).

Dipole-dipole forces: Forces between two polar molecules

Induced dipole forces or London forces: Forces between non-polar molecules

Hydrogen bonding: Forces between molecules in which hydrogen is covalently bonded to nitrogen, oxygen or fluorine – a special case of dipole-dipole forces

Intermolecular forces

Intermolecular forces determine many physical properties of substances:

Intermolecular forces: An attraction between molecules

Interatomic (intramolecular) forces: An electrostatic force of attraction between atoms due to the sharing or transfer of electrons

Boiling point: The temperature at which the vapour pressure of a substance equals atmospheric pressure. The stronger the intermolecular forces, the higher the boiling point.

Melting point: The temperature at which the solid and liquid phases of a substance are at equilibrium. The stronger the intermolecular forces, the higher the melting point.

Vapour pressure: The pressure exerted by a vapour at equilibrium with its liquid in a closed system. The stronger the intermolecular forces, the lower the vapour pressure.

Organic molecules

Organic chemistry is the study of carbon-based compounds:

Organic molecules: Molecules containing carbon atoms.

Molecular formula: A chemical formula that indicates the type of atoms and the correct number of each in a molecule.

Structural formula: A structural formula of a compound shows which atoms are attached to which within the molecule. Atoms are represented by their chemical symbols and lines are used to represent ALL the bonds that hold the atoms together.

Condensed structural formula: This notation shows the way in which atoms are bonded together in the molecule, but DOES NOT SHOW ALL bond lines.

Hydrocarbon: Organic compounds that consist of hydrogen and carbon only.

Homologous series: A series of organic compounds that can be described by the same general formula OR in which one member differs from the next with a CH₂ group.

Saturated compounds: Compounds in which there are no multiple bonds between C atoms in their hydrocarbon chains.

Unsaturated compounds: Compounds with one or more multiple bonds between C atoms in their hydrocarbon chains.

Functional group: A bond or an atom or a group of atoms that determine(s) the physical and chemical properties of a group of organic compounds.

Functional groups

Different functional groups define different classes of organic compounds:

Alkanes: Only C-H and C-C single bonds.

Alkenes: Carbon-carbon double bond.

Alkynes: Carbon-carbon triple bond.

Haloalkanes (X = F, Cℓ, Br, I): Halogen atom bonded to a saturated C atom.

Alcohols: Hydroxyl group bonded to a saturated C atom.

Aldehydes: Formyl group.

Ketones: Carbonyl group bonded to two C atoms.

Carboxylic acids: Carboxyl group.

Esters: [Definition provided in diagram structure]

Structural isomers

Isomers are compounds with the same molecular formula but different structures:

Structural isomer: Organic molecules with the same molecular formula, but different structural formulae.

Chain isomers: Same molecular formula, but different types of chains, e.g. butane and 2-methylpropane.

Positional isomers: Same molecular formula, but different positions of the side chain, substituents or functional groups on the parent chain, e.g. 1-choropropane and 2-chloropropane or but-2-ene and but-1-ene.

Functional isomers: Same molecular formula, but different functional groups, e.g. methyl methanoate and ethanoic acid.

Organic reactions

Organic compounds undergo various types of reactions:

Hydrohalogenation: The addition of a hydrogen halide to an alkene.

Halogenation: The reaction of a halogen (Br₂, Cℓ₂) with a compound.

Hydration: The addition of water to a compound.

Hydrogenation: The addition of hydrogen to an alkene.

Dehydrohalogenation of haloalkanes: The elimination of hydrogen and a halogen from a haloalkane.

Dehydration of alcohols: Elimination of water from an alcohol.

Cracking of alkanes: The chemical process in which longer chain hydrocarbon molecules are broken down to shorter more useful molecules.

Hydrolysis: The reaction of a compound with water.

Polymers

Polymers are large molecules made from repeating units:

Macromolecule: A molecule that consists of a large number of atoms.

Polymer: A large molecule composed of smaller monomer units covalently bonded to each other in a repeating pattern.

Monomer: Small organic molecules that can be covalently bonded to each other in a repeating pattern.

Polymerisation: A chemical reaction in which monomer molecules join to form a polymer.

Addition polymerisation: A reaction in which small molecules join to form very large molecules by adding on double bonds.

Addition polymer: A polymer formed when monomers (usually containing a double bond) combine through an addition reaction.

Condensation polymerisation: Molecules of two monomers with different functional groups undergo condensation reactions with the loss of small molecules, usually water.

Condensation polymer: A polymer formed by two monomers with different functional groups that are linked together in a condensation reaction in which a small molecule, usually water, is lost.

Energy and change

Energy changes accompany all chemical reactions:

Heat of reaction ($\Delta H$): The energy absorbed or released in a chemical reaction.

Exothermic reactions: Reactions that release energy. $\Delta H < 0$

Endothermic reactions: Reactions that absorb energy. $\Delta H > 0$

Activation energy: The minimum energy needed for a reaction to take place.

Activated complex: The unstable transition state from reactants to products.

Rate and extent of reaction

Understanding reaction rates is important for controlling chemical processes:

Reaction rate: The change in concentration of reactants or products per unit time.

Positive catalyst: A substance that increases the rate of a chemical reaction without itself undergoing a permanent change.

Chemical equilibrium

Many reactions reach a state of dynamic equilibrium:

Open system: An open system continuously interacts with its environment so that matter and energy can be exchanged with the surroundings.

Closed system: A closed system can exchange energy (as heat or work) but not matter, with its surroundings.

Reversible reaction: A reaction is reversible when products can be converted back to reactants.

Chemical equilibrium: It is a dynamic equilibrium when the rate of the forward reaction equals the rate of the reverse reaction.

Acids and bases

Acids and bases are fundamental to many chemical processes:

Arrhenius theory

Arrhenius theory: Acid: An acid is a substance that produces hydrogen ions (H⁺) / hydronium ions (H₃O⁺) when it dissolves in water.

Arrhenius theory: Base: A base is a substance that produces hydroxide ions (OH⁻) when it dissolves in water.

Lowry-Brønsted theory

Lowry-Brønsted theory: Acid: An acid is a proton (H⁺ ion) donor

Lowry-Brønsted theory: Base: A base is a proton (H⁺ ion) acceptor.

Strength of acids and bases

Strong acids: Strong acids ionise completely in water to form a high concentration of H₃O⁺ ions. Examples of strong acids are hydrochloric acid, sulphuric acid and nitric acid.

Strong bases: Strong bases dissociate completely in water to form a high concentration of OH⁻ ions. Examples of strong bases are sodium hydroxide and potassium hydroxide.

Weak acids: Weak acids ionise incompletely in water to form a low concentration of H₃O⁺ ions. Examples of weak acids are ethanoic acid and oxalic acid.

Weak bases: Weak bases dissociate/ionise incompletely in water to form a low concentration of ions. Examples of weak bases are ammonia, sodium carbonate, potassium carbonate, calcium carbonate and sodium hydrogen carbonate.

Concentration of acids and bases

Concentrated acids/bases: Concentrated acids/bases contain a large amount (number of moles) of acid/base in proportion to the volume of water.

Dilute acids/bases: Dilute acids/bases contain a small amount (number of moles) of acid/base in proportion to the volume of water.

Additional acid-base concepts

Conjugate acid-base pairs: When the acid, HA, loses a proton, its conjugate base, A⁻, is formed. When the base, A⁻, accepts a proton, its conjugate acid, HA, is formed. These two are a conjugate acid-base pair.

Ampholyte/ Amphiprotic: A substance that can act as either acid or base. Water is a good example of an Ampholyte.

Hydrolysis: The reaction of a salt with water.

Equivalence point: The equivalence point of a titration is the point at which the acid/base has completely reacted with the base/acid.

Endpoint: The endpoint of a titration as the point where the indicator changes colour.

pH scale: A scale of numbers from 0 to 14 used to express the acidity or alkalinity of a solution.

$K_w$: The equilibrium constant for the ionisation of water or the ionic product of water or the ionisation constant of water, $K_w = [\text{H}_3\text{O}^+][\text{OH}^-] = 1 \times 10^{-14}$ by 298 K.

Auto-ionisation of water: The reaction of water with itself to form H₃O⁺ ions and OH⁻ ions.

Electrochemical reactions

Electrochemistry involves the interconversion of chemical and electrical energy:

Galvanic cell: A cell in which chemical energy is converted into electrical energy. A galvanic (voltaic) cell has self-sustaining electrode reactions.

Electrolytic cell: A cell in which electrical energy is converted into chemical energy.

Oxidation: A loss of electrons. An increase in oxidation number.

Reduction: A gain of electrons. A decrease in oxidation number

Oxidising agent: A substance that is reduced/gains electrons.

Reducing agent: A substance that is oxidised/loses electrons.

Anode: The electrode where oxidation takes place.

Cathode: The electrode where reduction takes place.

Electrolyte: A solution/liquid/dissolved substance that conducts electricity through the movement of ions.

Electrolysis: The chemical process in which electrical energy is converted to chemical energy OR the use of electrical energy to produce a chemical change.

Chemical industry

Understanding the impact of chemistry on the environment is important:

Eutrophication: The process by which an ecosystem, e.g. a river or dam, becomes enriched with inorganic plant nutrients, especially phosphorus and nitrogen, resulting in excessive plant growth. As plant growth becomes excessive, the amount of dead and decaying plant material increases rapidly.