Unit 5: Energetics and Thermochemistry
Thermochemistry explores energy changes accompanying chemical reactions, particularly heat exchange. The chapter delves into enthalpy changes, calorimetry methods to measure heat flow, and the significance of Hess’s Law in calculating enthalpy changes. Additionally, it discusses bond enthalpies to estimate reaction energetics, highlighting the interaction of enthalpy, entropy, and spontaneity in chemical processes.
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What we have learnt
- Enthalpy is defined as the heat exchanged at constant pressure.
- Calorimetry allows for direct measurement of enthalpy changes through controlled reactions.
- Hess's Law states that the total enthalpy change for a reaction is the same irrespective of the pathway taken.
Key Concepts
- -- Enthalpy (H)
- A thermodynamic quantity defined as the internal energy of a system plus the product of pressure and volume, H = E + PV.
- -- Exothermic Reaction
- A chemical reaction that releases heat to the surroundings, resulting in a negative enthalpy change (ΔH < 0).
- -- Endothermic Reaction
- A chemical reaction that absorbs heat from the surroundings, resulting in a positive enthalpy change (ΔH > 0).
- -- Hess's Law
- A principle stating that the total enthalpy change of a reaction is the same whether it occurs in a single step or multiple steps.
- -- Bond Enthalpy
- The energy required to break one mole of a bond in a molecule in the gas phase, expressed in kJ/mol.
- -- Gibbs Free Energy (ΔG)
- A thermodynamic potential that determines spontaneity of processes, calculated as ΔG = ΔH - TΔS.
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