Thermo part 2
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This document discusses different types of enthalpy changes (ΔH) in thermochemistry including: 1) Enthalpy changes of formation (ΔHf) which is the energy released or absorbed to form 1 mole of a compound from its elements. 2) Enthalpy changes of decomposition (ΔHd) which is the energy released or absorbed when 1 mole of a compound decomposes into its elements. 3) Enthalpy changes of combustion (ΔHc) which is the energy released when 1 mole of a compound burns in oxygen. It also discusses methods to calculate enthalpy changes including calorimetry and using Hess's law.
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- 2. Kinds of Entalphi Changes (ΔH) 1. Entalphi Changes of Formation (ΔHf ) • Energy or heat that is released or absorbed to form 1 mol of compound from its free element. • Example : Formation reaction of NH4Cl : ½ N2 (g) + 2H2 (g) + ½ Cl2 (g) → NH4Cl (s) ΔHf = – 450 kj/mol
- 3. 2. Entalphi Changes of Decomposition (ΔHd ) • Energy or heat that is released or absorbed to decompose 1 mol of compound become its free element. • Entalphi Changes of decomposition is the inverse of entalphi changes of formation. • Example : Decomposition reaction of NH4Cl : NH4Cl (s) → ½ N2 (g) + 2H2 (g) + ½ Cl2 (g) ΔHd= + 450 kj/mol
- 4. 3. Entalphi Changes of Combustion (ΔHc ) • Energy or heat that is released when 1 mol of compound is burnt with oxygen. • Hydrocarbon compound is burnt to produce CO2 gas and water molecule (H2O) • Example : Combustion reaction of C2H5OH : C2H5OH + 3O2 → 2CO2 + 3H2O ΔHc = – 750 kj/mol
- 5. Calculating Entalphi Changes (ΔH) CALORIMETRY ΔH = ± m.c.ΔT FORMATION ΔHf product – ΔHf reactant HEAT (ΔHf) ΔHREACTION HESS’s LAW BONDING En.Ikat reactant – En.Ikat product ENERGY
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