Reaction Profiles

Reaction Profiles

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• Bildunterschrift: Endothermic Energy Level Diagram
• An energy level diagram can be used to show how the energy stored in chemicals changes during a chemical reaction. In endothermic reactions the products have more energy than the reactants. In exothermic reactions the products have less energy than the reactants.

Making and Breaking Bonds

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• Bildunterschrift: Bonds broken and made in an endothermic reaction

Bond Energy

• Bond energy is measured in kj/mol. We can use bond energy to calculate the energy change for many reactions. The energy released when a bond is formed or absorbed when it is broken is called the bond energy.
• e.g. the C-H bond in methane has a bond energy of 413 kj/mol
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• Bildunterschrift: All chemical reactions involve the breaking of old bonds followed by the making of new bonds.

Bond Energy

• To calculate the standard enthalpy of reactions:
• Sum of bond enthalpies of bonds broken - sum of bond enthalpies of bonds made
• ((2x497) +(4x413))-((2x405)+(4x463))
• = -816kj/mol
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• Bildunterschrift: Enthalpy of bonds

Enthalpies of Reactions

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• Bildunterschrift: Bond enthalpies