Physics and Chemistry Key Definitions

Vocabulary flashcards covering fundamental definitions in Physics and Chemistry including mechanics, energy, electromagnetism, chemical reactions, acids and bases, and organic chemistry.

Vector

A physical quantity that has both magnitude and direction.

Scalar quantity

A physical quantity that has magnitude only.

Resultant vector

The single vector which has the same effect as the original vectors acting together.

Distance

The length of path travelled; distance is a scalar quantity.

Displacement

A change in position.

Speed

The rate of change of distance; speed is a scalar quantity.

Velocity

The rate of change of position or the rate of displacement or the rate of change of displacement; velocity is a vector quantity.

Acceleration

The rate of change of velocity.

Weight ($F_g$)

The gravitational force the Earth exerts on any object on or near its surface.

Normal force ($F_N$)

The perpendicular force exerted by a surface on an object in contact with it.

Frictional force ($F_f$)

The force that opposes the motion of an object.

Newton's first law

An object continues in a state of rest or uniform (moving with constant) velocity unless it is acted upon by a net or resultant force.

Inertia

The property of an object that causes it to resist a change in its state of rest or uniform motion.

Newton's second law

When a net force, $F_{net}$, is applied to an object of mass, $m$, it accelerates in the direction of the net force. The acceleration, $a$, is directly proportional to the net force and inversely proportional to the mass.

Newton's third law

When object A exerts a force on object B, object B simultaneously exerts an oppositely directed force of equal magnitude on object A.

Linear momentum

The product of the mass and velocity of the object.

Newton's second law (in terms of momentum)

The net force acting on an object is equal to the rate of change of momentum.

Law of conservation of linear momentum

The total linear momentum of an isolated system remains constant (is conserved).

Elastic collision

A collision in which both momentum and kinetic energy are conserved.

Inelastic collision

A collision in which only momentum is conserved.

Impulse ($J$)

The product of the net force and the contact time.

Work done

The product of the displacement and the component of the force parallel to the displacement.

Gravitational potential energy

The energy an object possesses due to its position relative to a reference point.

Kinetic energy

The energy an object has as a result of the object's motion.

Mechanical energy

The sum of gravitational potential and kinetic energy at a point.

Law of conservation of energy

The total energy in a system cannot be created nor destroyed, only transformed from one form to another.

Principle of conservation of mechanical energy

In the absence of air resistance or any external forces, the mechanical energy of an object is constant.

Work-energy theorem

The work done by a net force on an object is equal to the change in the kinetic energy of the object.

Power

The rate at which work is done or the rate at which energy is transferred.

Efficiency

The ratio of output power to input power.

Newton's Law of Universal Gravitation

Every particle with mass in the universe attracts every other particle with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Gravitational field

The force acting per unit mass.

Coulomb's law

Two point charges exert forces on each other; the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges.

Electric field at a point

The force per unit positive charge.

Potential difference

The work done per unit positive charge.

Current

The rate of flow of charge.

Ohm's Law

The current through a conductor is directly proportional to the potential difference across the conductor at constant temperature.

Emf

The total energy supplied per coulomb of charge by the cell.

Magnetic flux linkage ($N ext{\Phi}$)

The product of the number of turns on the coil and the flux through the coil.

Faraday's law of electromagnetic induction

The emf induced is directly proportional to the rate of change of magnetic flux (flux linkage).

Lenz's law

The induced current flows in a direction so as to set up a magnetic field to oppose the change in magnetic flux.

Diode

A component that only allows current to flow in one direction.

Threshold (cut-off) frequency ($f_o$)

The minimum frequency of incident radiation at which electrons will be emitted from a particular metal.

Work function ($W_o$)

The minimum amount of energy needed to emit an electron from the surface of a metal.

Molar mass

The mass in grams of one mole of that substance.

Molar concentration

The amount of solute per unit volume of solution.

Electronegativity

A measure of the tendency of an atom to attract a bonding pair of electrons.

Heat of reaction ($\Delta H$)

The net change of chemical potential energy of the system.

Exothermic reactions

Reactions which transform chemical potential energy into thermal energy.

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 transition state between the reactants and the products.

Reaction rate

The change in amount or concentration per unit time of either a reactant or product.

Catalyst

A substance that increases the rate of the reaction but remains unchanged at the end of the reaction.

Closed system (chemistry)

One in which mass is conserved inside the system but energy can enter or leave the system freely.

Open system (chemistry)

One in which both energy and matter can be exchanged between the system and its surroundings.

Le Ch\u00e2telier'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.

Acid (Lowry-Br\u00f8nsted)

Defined as a proton donor.

Base (Lowry-Br\u00f8nsted)

Defined as a proton acceptor.

Ionisation

The reaction of a molecular substance with water to produce ions.

Strong acid

An acid that ionises almost completely in an aqueous solution.

Weak acid

An acid that only ionises partially in an aqueous solution.

Dissociation

The splitting of an ionic compound into its ions.

Strong base

A base that dissociates almost completely in an aqueous solution.

Weak base

A base that only ionises partially in an aqueous solution.

Amphoteric substance

A substance that can act as either an acid or a base; also known as amphiprotic.

Salt

A substance in which the hydrogen of an acid has been replaced by a cation.

Hydrolysis of a salt

A reaction of an ion (from a salt) with water.

Neutralisation

A chemical reaction in which an acid and a base react so that neither is in excess.

Standard solution

A solution of known concentration.

Redox reaction

A reaction involving the transfer of electrons.

Oxidation

The loss of electrons.

Reduction

The gain of electrons.

Oxidising agent

A substance that accepts electrons.

Reducing agent

A substance that donates electrons.

Anode

The electrode where oxidation takes place.

Cathode

The electrode where reduction takes place.

Electrolyte

A substance that can conduct electricity due to the presence of free (mobile) ions when molten or dissolved in solution.

Hydrocarbon

A compound containing only carbon and hydrogen atoms.

Saturated compound

A compound in which all of the bonds between carbon atoms are single bonds.

Unsaturated compound

A compound in which there is at least one double and/or triple bond between carbon atoms.

Functional group

An atom or a group of atoms that form the centre of chemical activity in the molecule.

Homologous series

A series of similar compounds which have the same functional group and have the same general formula, in which each member differs from the previous one by a single $CH_2$ unit.

Structural isomers

Compounds having the same molecular formula but different structural formulae.