Enthalpy change, exothermic and endothermic reactions Video link: https://youtu.be/zSTbTn5t27A

1. Enthalpy Changes
Chapter 6
Part 1
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2. Exothermic and endothermic reactions:
• Exothermic reaction: chemical reaction that release energy to the
surroundings
• Example: reaction of magnesium and sulfuric acid to produce
magnesium sulfide
• Endothermic reaction: chemical reaction that absorb energy from the
surrounding
• Example dissolving of ammonium chloride in water
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3. Enthalpy change:
Enthalpy change is the energy exchange between a chemical reaction and
its surroundings at constant pressure.
Enthalpy (H): total energy associated with the materials that react
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4. How to calculate enthalpy change?
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Unit of enthalpy change is kilojoules per mole (kJ mol-1)

5. Reaction pathway (enthalpy profile diagram):
• Y-axis: enthalpy of reactants and
products
• X-axis: reaction pathway with reactant
on the left and product on the right.
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6. Exothermic reaction:
• Energy is released to the surrounding
• Enthalpy of reactants is higher than products
• H Products – H Reactants is negative
• Example:
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7. Endothermic reaction:
• Energy is absorbed from the
surrounding
• Enthalpy of reactants is lower than
products
• H Products – H Reactants is positive
• Example:
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8. Standard enthalpy change of combustion ΔHO
c
• Substance that is combusted can be element or compound
• Enthalpy always exothermic and have negative value
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9. Standard enthalpy change of neutralisation, ΔHO
n
• Is the enthalpy change when one mole of water is formed by the
reaction of an acid with alkali under standard conditions
• Example:
• Cl- and Na+ are spectator ions
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10. Standard enthalpy change of solution, ΔHO
sol
• Is enthalpy change when one mole of solute is dissolved in a solvent to
form an infinitely dilute solution under standard conditions.
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11. Standard enthalpy change of hydration of an
anhydrous salt:
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12. End of Video
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