chemical energetics

Formula for enthalpy change

∆H = total energy of bonds broken - total energy of bonds formed

What happens to thermal energy and energy levels during exothermic reactions?

• Thermal energy released

• Energy level of system decreases, energy level of surroundings increases

• Negative enthalpy change

What is the difference between the energy of bond forming and breaking during exothermic reactions?

H(bond forming) > H(bond breaking)

What are some processes that are exothermic reactions?

• Neutralisation

• Respiration

• Inside heat packs and self-heating pots

Why are exothermic reactions more stable than endothermic ones?

• Lower final energy level, so lower Ea required

Enthalpy change graph of an exothermic reaction

What happens to thermal energy levels during endothermic reactions?

• Thermal energy is absorbed

• Energy level of system increases, energy level of surroundings decreases

• Positive enthalpy change

What is the difference between the energy of bond forming and breaking during endothermic reactions?

H(bond breaking) > H(bond forming)

What are some processes that are endothermic reactions?

• thermal decomposition

• photosynthesis

• inside a cooling pack

Enthalpy change graph of an endothermic reaction

What is bond energy?

The amount of energy absorbed or released to break one mole of a chemical bond

• Each chemical bond has a specific bond energy associated with it

What is activation energy? (Ea)

The minimum amount of energy that colliding reactant particles must possess to react with each other