Energy Level Diagrams

• Show energy changes in reaction

Understanding

Show overall enthalpy change of reaction

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Exothermic Reactions - Energy Level Diagram

• Energy cannot be created or destroyed, and it can only be changed from 1 form to another and there is energy content in a substance. Energy
• As exothermic reaction → gives heat to surroundings → total energy of products ($E_p$) will be lower than the total energy of the reactants ($E_r$)
• Since $E_P<E_r$, $E_P-E_r=negative(-ve)$

Difference in energy level of reactant and products in exothermic reaction can be represented by energy level diagram $\Delta H=E_P-E_r=-ve$ (from diagram $E_r>E_p$)

• In exothermic reaction → products are more energetically stable because → they have less energy than the reactants. Products are more stable at lower energy levels. Thus, many reactions which occurs spontaneously are exothermic reactions

Endothermic Reactions - Energy Level Diagram

• Energy cannot be created or destroyed, and it can only be changed from 1 form to another and there is energy content in a substance. Energy

• As endothermic reaction absorbs heat from the surroundings → total energy of the products ($E_P$) will be higher than the total energy of the reactants ($E_r$)

• Since $E_P>E_r$ $\Delta H=totalenergyofproducts-totalenergyofreactants$ = $E_{P}- E_{r} = positive(+ve_)

• difference in energy level of reactants and products in endothermic reaction can be represented by energy level diagram

• In endothermic reaction → products are less energetically stable → because they have more energy than the reactants. Products are unstable at higher energy levels hence they will break down easily.

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Notes:

• note that the amount of energy released is proportion to amt of substance. if x joules released for 1 mole, then 2x joules released for 2 moles

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