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42 Cards in this Set

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Exothermic Reaction

A reaction that gives out energy and heats the surroundings.

Endothermic Reaction

A reaction that takes in energy and cools the surroundings.

3 things for Standard conditions:

- 298K / 25 degrees C

- A standard pressure of 1 atmosphere (atm)

- A standard concentration of 1 moldm -3 for solutions.

Standard States

The physical state of a substance under standard conditions. This may be a pure solid, liquid or gas.

Standard Enthalpy Change for a Reaction


The enthalpy change when one molar quantities of reactants as stated in the equation react together under standard conditions.

Kelvin (K)

273K = 0 degrees C.

Standard Enthalpy Change of Combustion


The enthalpy change that occurs when 1 mole of a substance is burnt completely in excess oxygen under standard conditions in standard states.

Standard Enthalpy Change of Formation


The enthalpy change when 1 mole of a compound is formed from its elements under standard conditions in standard states.

Standard Enthalpy Change of Neutralisation


The enthalpy change when 1 mole of hydrogen ions react with 1 mole of hydroxide ions to form 1 mole of water under standard conditions and in solutions containing 1 moldm-3.

Specific Heat Capacity of a substance (c)

The amount of energy needed to raise the temperature of 1g of a substance by 1K.

Aromatic Compounds

Compounds that contain one or more benzene rings.

Aliphatic Compounds

Compounds that do not contain any benzene rings.

Functional Group

Modifiers that are responsible for the characteristic chemical reactions of molecules.


Hydrocarbons containing the maximum number of hydrogen atoms possible, with no double or triple bonds between carbon atoms.

Molecular Formula

The number of atoms of each element in a compound.

Homologous Series

A series of compounds in which all members have the same general molecular formula.

Average Bond Enthalpy

The average quantity of energy needed to break a particular bond.


Any reaction in which a larger molecule is made into smaller molecules.


Any organic compound that has a double or triple bond between carbon atoms.

Hess's Law

The enthalpy change for a particular reaction will always be the same and is independent of the pathway taken providing that starting and finishing conditions are the same.


A substance that speeds up a reaction but can be chemically unchanged at the end. A catalyst always lowers the activation enthalpy and can provide an alternative pathway for the reaction.


The process of speeding up a chemical reaction using a catalyst.

Homogeneous Catalysis

When the reactants and products are in the same physical state as the catalyst.

Heterogeneous Catalysis

When the reactants and products are in different physical states to the catalyst.

Catalyst poison

Poison adsorbs (sticks) more strongly than reactants

So reactant molecules can't bond with the surface of the catalyst.


A species which can act as an electron pair acceptor and is attracted to a region of high electron density such as a double bond. They are usually + or delta +


An ion with a positively-charged carbon atom.

Addition reaction

A reaction where two or more molecules react to form a single larger molecule.


Small molecules called monomers join together to produce long chain polymers.


A compound which contains hydrogen and carbon atoms ONLY.


An aromatic hydrocarbon.

Test for Unsaturation

Shake the substance with bromine water.

The bromine is decolourised (red-brown to colourless) if the substance is unsaturated.

Structural Isomer

Same molecular or chemical formula

Different structural arrangement of atoms


Occurs in compounds with C=C double bond.

Owing to the lack of free rotation (locked by the pi bond)

E/X pair where each C of the C=C has a hydrogen atom


A polymer which can be deformed and later return to its original size and shape

Steps in Heterogeneous Catalysis

Gas molecules are adsorbed (stick) onto the catalyst surface.

Bonds in reactants weaken and break

New bonds and molecules (products) form

Products diffuse away from the catalyst surface.





Why a reaction is exothermic or gives out heat?

Bonds broken in reactants - energy in

New bonds formed in products - energy released

Greater energy released than taken in so overall there is an output of energy = exothermic.

Why experimental enthalpy values are different from those in a data book?

Bond enthalpies are only average values and vary between molecules

Chemicals are not in their standard states in the given example.

Sigma bond

The end-on overlap of electron orbitals (s with s, s with p, p with p) so that the shared pair of electrons is an area of increased electron density along the internuclear line between the atoms.

Pi bond

The lateral overlap of p electron orbitals so that the shared pair of electrons consists of two areas of increased electron density above and below the internuclear line between the atoms.