Chemistry - Chemical energetics

Exothermic reaction

When energy is given out/released (exits). Thermal energy is transferrred from the system to the surroundings. TThe energy of the system decrease, so the energy change is negative. The temperature of the surroundings increase. E.g combustion, handwarmers

Endothermic

Energy is taken in/absorbed. Thermal energy is transferred from the surroundings into the system. The energy of the system increases meaning the energy change is positive. The temperature of the surrounding decreases.

Activation energy

The minimum amount of energy required for a successful collision to happen and for a reaction to take place. Different reactions have different activation energies

Enthaply change

The transfer of thermal energy during a reaction. Represented by Δ H

Enthaply change for endothermic reaction

Positive as energy taken in is more than the energy given out

Enthaply change for exothermic reaction

Negative, energy taken in is less than the energy given out

Bond breaking and bond forming

Whether a reaction is endothermic or exothermic depends