IB Chemistry Topic 5 - Energetics

Exothermic Reaction

When the bonds in the products are stronger than the bonds in the reactants and the reaction gives off heat

Endothermic Reaction

When the bonds in the reactants are stronger than the bonds in the products and the reaction absorbs heat

Two examples of exothermic processes are_____

Combustion and Neutralization reactions

Enthalpy, H

The internal energy stored in the reactants

ΔH

The difference in the enthalpy of the reactants and the products

Standard enthalpy change of a reaction

ΔH of a reaction under 1atm of pressure and at 298K

Heat

A measure of the total energy in a given amount of substance

Temperature

A measure of the "hotness" of a substance

ΔH of exothermic

negative, products more stable than reactants

ΔH of endothermic

positive, reactants more stable than products

Equation for enthalpy changes

Heat energy = mass(m) x specific heat capacity (c) x temperature change (ΔT)

Standard units for enthalpy changes

Heat energy(kJ), mass(kg), temperature(K)

bond enthalpy

the energy change when one mol of a covalent bond in the gaseous state is formed from its gaseous atoms