Chem topic 3 -> Enthalpy

What does the enthalpy profile look like for an exothermic reaction

What does the enthalpy profile look like for an endothermic reaction

Define activation energy

Minimum energy required for a successful reaction to occur

Define enthalpy of formation

• Enthalpy change when 1 mol of a compound is formed from its elements in their standard states

Define enthalpy of combustion

• Enthalpy change when 1 mol of a substance in its standard state is burnt in excess oxygen

Define enthalpy of neutralisation

• Enthalpy change when 1 mol of water is formed by reacting an acid and alkali

How can enthalpy be measured

q = m x c x delta T

q → energy in joules

m → mass in g

c → Specific heat capacity → 4.18 J/g/degree

Define bond enthalpy → specific to each bond

Amount of energy needed to break 1 mol of a specific covalent bond in the gaseous state

Why is bond energy an average

• Bond energy is an average of the bond enthalpies of a specific covalent bond in different molecules

Calculating enthalpy change from bond energies

Bonds broken requires energy → endothermic

Bonds made releases energy → exothermic

Enthalpy change = Enthalpy change for bonds broken + Enthalpy change for bonds made