Energetic/Thermochemistry (IB)

Energetics

The study of heat changes in chemical reactions.

Heat

A form of energy, measured as the total energy content of a substance during a reaction.

Temperature

Measures how hot or cold something is, related to the average kinetic energy of particles.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed.

Second Law of Thermodynamics

For a reaction to occur spontaneously, there must be an increase in entropy.

Entropy

A measure of disorder in a system.

Enthalpy (ΔH)

The heat energy stored in a substance, primarily in its chemical bonds.

Heat energy (Q) formula

Q = mcΔT, where m is mass, c is specific heat capacity, and ΔT is the change in temperature.

Standard Conditions

Defined as 100 kPa pressure, 1 mol/dm³ concentration, and usually 298 K temperature.

Standard Enthalpy Change of Reaction (ΔHᵣ)

Enthalpy change when reactants react to form products under standard conditions.

Standard Enthalpy Change of Formation (ΔHᶠ)

Enthalpy change when 1 mole of a compound is formed from its elements under standard conditions.

Standard Enthalpy Change of Combustion (ΔH_c)

Enthalpy change when 1 mole of a substance is burned in excess oxygen under standard conditions.

Exothermic Reactions

Reactions that release heat to the surroundings; ΔH is negative.

Endothermic Reactions

Reactions that absorb heat from the surroundings; ΔH is positive.

Calorimeter

A device used to measure heat changes in reactions.

Specific Heat Capacity (c)

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

Hess’s Law

The total enthalpy change for a reaction is the same, regardless of the route taken.

Bond Enthalpy

The energy required to break a bond, which can be used to calculate enthalpy changes.

Born-Haber Cycle

A method used to calculate lattice enthalpy of ionic compounds through a series of steps.

Gibbs Free Energy (ΔG)

Combines enthalpy and entropy to predict whether a reaction is spontaneous.

ΔG equation

ΔG = ΔH - TΔS, where T is the temperature.

Entropy Change (ΔS)

Calculated as ΔS = Sproducts - Sreactants.

Enthalpy of Combustion of Propan-1-ol

ΔH = -1,474 kJ/mol, calculated from the combustion reaction.

Standard Enthalpy Change of Neutralization (ΔH_neut)

Enthalpy change when 1 mole of water is formed by an acid-base reaction.

Reactivity of Ice and Water

Ice has lower kinetic energy compared to boiling water, illustrating differences in temperature.

Reaction Conditions

Factors like pressure, concentration, and temperature that affect chemical reactions under standard state.