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Thermochemistry & Thermodynamics

Enthalpy

A thermodynamic state function equal to internal energy plus the product of pressure and volume.

H = U + pV kJ/mol Thermochemistry & Thermodynamics

Enthalpy Level Diagram

A diagram plotting the enthalpies of reactants and products to show the direction and size of the enthalpy change.

kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Atomisation

The enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.

ΔH_at° kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Dilution

The enthalpy change when a solution is diluted from one concentration to another by adding solvent.

ΔH_dil kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Fusion

The enthalpy change when one mole of a solid melts to a liquid at its melting point.

ΔH_fus kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Neutralisation

The enthalpy change when an acid and a base react to form one mole of water under standard conditions.

H⁺ + OH⁻ → H₂O, ΔH = −57.1 kJ kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Reaction

The heat absorbed or released when a reaction occurs at constant pressure in the molar amounts of the balanced equation.

ΔH_rxn = ΣΔH_f(products) − ΣΔH_f(reactants) kJ/mol Solutions & Colligative Properties

Enthalpy of Solution

The heat absorbed or released when one mole of a substance dissolves completely in a large excess of solvent.

ΔH_sol = ΔH_lattice + ΔH_hyd kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Sublimation

The enthalpy change when one mole of a solid converts directly into vapour.

ΔH_sub = ΔH_fus + ΔH_vap kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Vaporisation

The enthalpy change when one mole of a liquid becomes vapour at its boiling point.

ΔH_vap kJ/mol Thermochemistry & Thermodynamics

Entropy

A measure of the dispersal of energy and the number of microscopic arrangements available to a system.

S = k ln W J/(mol·K) Thermochemistry & Thermodynamics

Entropy Change of the Surroundings

The entropy change experienced by the surroundings when they absorb or release heat from a system.

ΔS_surr = −ΔH_sys / T J/K Biochemistry & Polymer Chemistry

Enzyme

A biological catalyst, almost always a protein, that accelerates a specific biochemical reaction.

Dimensionless Chemical Kinetics & Catalysis

Enzyme Catalysis

Catalysis by protein molecules that bind substrates at a specific active site and lower the activation energy dramatically.

Dimensionless Biochemistry & Polymer Chemistry

Enzyme Specificity

The ability of an enzyme to select one substrate, or one class of substrate, and catalyse one particular reaction.

Dimensionless Chemical Equilibrium

Equilibrium Constant

The fixed ratio of product to reactant terms, each raised to its stoichiometric power, that characterises a reaction at a given temperature.

K = Π[products]^ν / Π[reactants]^ν Various Chemical Equilibrium

Equilibrium Constant of a Reversed Reaction

The constant obtained when a reaction is written in the opposite direction, equal to the reciprocal of the original.

K_reverse = 1 / K_forward Various Chemical Equilibrium

Equilibrium Constant of a Scaled Reaction

The constant obtained when every coefficient in an equation is multiplied by the same factor.

K_new = K_old^n Various Chemical Equilibrium

Equilibrium in Closed Systems

The requirement that no matter enters or leaves for a true chemical equilibrium to be established.

Dimensionless Chemical Equilibrium

Equilibrium Position

The particular set of concentrations at which a system settles, describing how far the reaction has proceeded.

mol/L Chemical Equilibrium

Equilibrium Yield

The proportion of reactant converted to product once equilibrium has been reached.

yield = n_product / n_theoretical Dimensionless Acids, Bases & Salts

Equivalence Point

The point in a titration at which exactly stoichiometric amounts of the two reactants have been combined.

n_acid × basicity = n_base × acidity mol Stoichiometry & Chemical Reactions

Equivalent Weight

The mass of a substance that combines with or displaces 1.008 g of hydrogen, 8 g of oxygen or one mole of electrons.

E = M / n-factor g/equiv Organic Chemistry

Ester

A compound formed by replacing the acidic hydrogen of a carboxylic acid with an alkyl group.

R–COO–R′ Dimensionless