5.4 Narrated Notes

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5.4 - Enthalpies of Reaction : 

5.4 - Enthalpies of Reaction

Enthalpies of Reaction : 

The enthalpy change for a given reaction is given by the enthalpy of the products minus the enthalpy of the reactants Formula Δ H = Hproducts - Hreactants 5.4 Enthalpies of Reaction

Enthalpies of Reaction : 

The enthalpy change that accompanies a reaction is called the enthalpy of reaction, or merely the heat of reaction 5.4 Enthalpies of Reaction

Enthalpies of Reaction : 

Balanced chemical equations that show the associated enthalpy changes are called thermochemical equations 5.4 Enthalpies of Reaction

Draw the enthalpy diagram of the reaction between hydrogen and oxygen : 

2 H2(g) + O2(g)2 H2O(g)ΔH = -483.6 kJ 5.4 Draw the enthalpy diagram of the reaction between hydrogen and oxygen

Guidelines for using thermochemical equations and enthalpy diagrams : 

Enthalpy is an extensive property The magnitude of ΔH is directly proportional to the amount of reactant consumed in the process 5.4 Guidelines for using thermochemical equations and enthalpy diagrams

Guidelines for using thermochemical equations and enthalpy diagrams : 

The enthalpy change for a reaction is equal in magnitude, but opposite in sign, to ΔH for the reverse reaction When we reverse a reaction, we reverse the role of the products and the reactants; thus the reactants in a reaction become the products of the reverse reaction 5.4 Guidelines for using thermochemical equations and enthalpy diagrams

Guidelines for using thermochemical equations and enthalpy diagrams : 

The enthalpy change for a reaction depends on the state of the reactants and products It is important to specify the state of the reactants and products in thermochemical reactions 5.4 Guidelines for using thermochemical equations and enthalpy diagrams

Practice Exercise : 

Hydrogen peroxide can decompose to water and oxygen by the following reaction: 2 H2O2(l) 2 H2O(l) + O2(g)ΔH = -196 kJ Calculate the value of q when 5.00 g of H2O2(l) decomposes at constant pressure 5.00 g H2O x1 mol H2O2x-196 kJ 34.0 g H2O22 mol H2O2 = -14.4 kJ 5.4 Practice Exercise