Exothermic + endothermic reactions

Law of conservation of energy

• energy can not be created or destroyed

• energy changes are referring to SYSTEM and SURROUNDING

• SYSTEM → chemcial reaction where bonds are broken and formed

• everything else is the SURROUNDING (including the reaction vessel, water used for dissolving etc)

• energy is lost/gained from the system to surrounding during a reaction

how do energy changes occur

• Chemical energy is stored in the bonds

• During a chemical reaction, bonds are broken and new bonds are formed.

• This involves rearrangement of atoms and redistribution of chemical energy

• Energy is released or absorbed depending on the relative bond energies of reactants and products, usually as heat

Exothermic

• heat is released

• chemical energy of products<reactants

• heat given to the surroundings

• temp increases

• COMBUSTION + respiration

Endothermic

• heat is absorbed

• chemical energy of products>reactants

• heat absorbed from the surroundings

• temp decreases

• PHOTOSYNTHESIS

Thermochemical equations

balanced chemical equations that also include magnitude of heat change in the reaction

• heat content or enthalpy → chemical energy of a substance

• EXCHANGE of heat energy between system + surrounding during a reaction → ENTHALPY CHANGE triangle H = Hp - Hr

• H + → endothermic

• H - → exothermic

Activation Energy

for breaking bonds → additional energy energy that the reactants must overcome to become products → its a barrier for both exothermic + endothermic reactions

Energy Profile Diagrams

REACTANTS products (exothermic) → less activation energy

reactants PRODUCTS (endothermic) → more activation energy