This document summarizes different types of enthalpy changes in chemical reactions. It defines exothermic reactions as releasing energy to the surroundings and endothermic reactions as absorbing energy from the surroundings. Enthalpy change is the energy exchange between a reaction and its surroundings at constant pressure. The document explains how to calculate enthalpy change and represents reaction pathways using enthalpy profile diagrams to show enthalpy changes for exothermic and endothermic reactions. It also defines standard enthalpy changes of combustion, neutralization, solution, and hydration of salts.

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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