Yishun Innova Junior College JC1 H2 Chemistry Topic 5(A) Chemical Energetics Thermochemistry

Flashcards for Yishun Innova Junior College JC1 H2 Chemistry Topic 5(A) Chemical Energetics Thermochemistry

Thermochemistry

The study of energy changes during chemical reactions.

System

The portion of the universe we single out for study.

Surroundings

Everything else in the universe that is not the system.

Closed System

A system where matter cannot be exchanged but energy can be transferred.

Isolated System

A system where neither matter nor energy can be exchanged.

Open System

A system where both matter and energy can be exchanged.

Enthalpy (H)

An indication of a substance's total heat energy content at constant pressure.

Enthalpy Change (ΔH)

The heat released or absorbed by the system during a reaction at constant pressure.

Exothermic Process

A process where heat is given off to the surroundings (ΔH < 0).

Endothermic Process

A process where heat is absorbed from the surroundings (ΔH > 0).

Activation Energy (Ea)

The minimum energy required for a reaction to occur.

Standard Enthalpy Change (ΔH°)

Enthalpy change measured under standard conditions.

Standard Conditions

298 K (25°C), 1 bar pressure, 1 mol dm-3 concentration.

Standard Enthalpy Change of Reaction (ΔHr°)

Heat change when molar quantities of reactants react together at 298 K and 1 bar.

Standard Enthalpy Change of Formation (ΔHf°)

Heat change when one mole of a compound is formed from its elements at 298 K and 1 bar.

Standard Enthalpy Change of Combustion (ΔHc°)

Heat evolved when one mole of a substance is completely burnt in excess oxygen at 298 K and 1 bar.

Standard Enthalpy Change of Neutralisation (ΔHn°)

Heat change when an acid and a base react to form one mole of water at 298 K and 1 bar.

Standard Enthalpy Change of Atomisation (ΔHatom°)

Heat absorbed when one mole of gaseous atoms is formed from its element at 298 K and 1 bar.

Ionisation Energy (IE)

Energy required to remove one mole of valence electrons from one mole of gaseous atoms.

Electron Affinity (EA)

Energy evolved when one mole of gaseous atoms accepts one mole of electrons to form one mole of gaseous singly charged negative ions.

Lattice Energy (LE)

Heat evolved when one mole of solid ionic compound is formed from its isolated gaseous ions.

Standard Enthalpy Change of Hydration (ΔHhyd°)

Heat evolved when one mole of gaseous ions dissolves in water to form hydrated ions at 298 K and 1 bar.

Standard Enthalpy Change of Solution (ΔHsol°)

Heat change when one mole of a substance is dissolved in water to form a solution at 298 K and 1 bar.

Bond Energy

Energy required to break one mole of covalent bonds between two atoms in a gaseous state.