ch06---energetics.ppt
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1、New Way Chemistry for Hong Kong A-Level Book 11Chapter 6Energetics6.1 What is Energetics?6.2 Ideal Enthalpy Changes Related to Breaking and Formation of Bonds6.3 Standard Enthalpy ChangesNew Way Chemistry for Hong Kong A-Level Book 126.4 Experimental Determination of Enthalpy Changes by Calorimetry6
2、.5 Hesss Law6.6 Calculations involving Enthalpy Changes of ReactionsNew Way Chemistry for Hong Kong A-Level Book 13What is Energetics?Energetics is the study of energy changes associated with chemical reactions.Thermochemistry is the study of heat changes associated with chemical reactions.Some term
3、sEnthalpy(H)=heat content in a substanceEnthalpy change(H)=heat content of products-heat content of reactants=Hp-Hr6.1 What is Energetics?(SB p.140)New Way Chemistry for Hong Kong A-Level Book 14Internal Energy and Enthalpye.g.Zn(s)+2HCl(aq)ZnCl2(aq)+H2(g)Heat change atconstant pressure=Change in in
4、ternal energy+Work done on the surroundings(Heat change at constant volume)Enthalpy change6.1 What is Energetics?(SB p.140)New Way Chemistry for Hong Kong A-Level Book 15Exothermic and Endothermic ReactionsAn exothermic reaction is a reaction that releases heat energy to the surroundings.(H=-ve)6.1
5、What is Energetics?(SB p.142)New Way Chemistry for Hong Kong A-Level Book 16Exothermic and Endothermic ReactionsAn endothermic reaction is a reaction that absorbs heat energy from the surroundings.(H=+ve)6.1 What is Energetics?(SB p.141)New Way Chemistry for Hong Kong A-Level Book 17Enthalpy Changes
6、 Related to Breaking and Forming of Bondse.g.CH4+2O2 CO2+2H2O 6.2 Enthalpy Changes Related to Breaking and Formation of Bonds?(SB p.143)In an exothermic reaction,the energy required in breaking the bonds in the reactants is less than the energy released in forming the bonds in the products(products
7、contain stronger bonds).New Way Chemistry for Hong Kong A-Level Book 18Enthalpy Changes Related to Breaking and Forming of BondsIn an endothermic reaction,the energy required in breaking the bonds in the reactants is more than the energy released in forming the bonds in the products(reactants contai
8、n stronger bonds).6.2 Enthalpy Changes Related to Breaking and Formation of Bonds?(SB p.143)New Way Chemistry for Hong Kong A-Level Book 19Bond EnthalpiesTo be discussed in later chapters.6.2 Enthalpy Changes Related to Breaking and Formation of Bonds?(SB p.143)BondMean Bond Enthalpy(kJ mol-1)H HC C
9、CCC CN NN NN N436348612837163409944New Way Chemistry for Hong Kong A-Level Book 110Standard Enthalpy ChangesCH4(g)+2O2(g)CO2(g)+2H2O(g)H=-802 kJ mol-1 CH4(g)+2O2(g)CO2(g)+2H2O(l)H=-890 kJ mol-1As enthalpy changes depend on temperature and pressure,chemists find it convenient to report enthalpy chang
10、es based on an internationally agreed set standard conditions:1.elements or compounds in their normal physical states;2.a pressure of 1 atm(101325 Nm-2);and3.a temperature of 250C(298 K)6.3 Standard Enthalpy Changes(SB p.144)Enthalpy change under standard conditions denoted by symbol:HNew Way Chemis
11、try for Hong Kong A-Level Book 111Standard Enthalpy Changes of ReactionsStandard Enthalpy Change of Neutralizatione.g.The standard enthalpy change of neutralization between HNO3 and NaOH is-57.3 kJ mol-1e.g.The standard enthalpy change of neutralization between HCl and NaOH is-57.1 kJ mol-16.3 Stand
12、ard Enthalpy Changes(SB p.144)The standard enthalpy change of neutralization(Hneut)is the enthalpy change when one mole of water is formed from the neutralization of an acid by an alkali under standard conditions.e.g.H+(aq)+OH-(aq)H2O(l)Hneut=-57.3 kJ mol-1New Way Chemistry for Hong Kong A-Level Boo
13、k 112Standard Enthalpy Changes of neutralizationH+(aq)+OH-(aq)H2O(l)6.3 Standard Enthalpy Changes(SB p.145)-57.1-57.2-52.2-68.6NaOHKOHNH3NaOHHClHClHClHF Hneu AlkaliAcidNew Way Chemistry for Hong Kong A-Level Book 113Standard Enthalpy Changes of ReactionsStandard Enthalpy Change of SolutionNote that
14、enthalpy changes of solution associate with physical changes.6.3 Standard Enthalpy Changes(SB p.146)The standard enthalpy change of solution(Hsoln)is the enthalpy change when one mole of a solute is dissolved to form an infinitely dilute solution under standard conditions.e.g.NaCl(s)+water Na+(aq)+C
15、l-(aq)Hsoln=+3.9 kJ mol-1e.g.LiCl(s)+water Li+(aq)+Cl-(aq)Hsoln=-37.2 kJ mol-1New Way Chemistry for Hong Kong A-Level Book 1146.3 Standard Enthalpy Changes(SB p.146)Standard Enthalpy Changes of solution-44.7+3.9-57.8+20.0NaOHNaClKOHKBrHsoln(kJ mol-1)SaltNew Way Chemistry for Hong Kong A-Level Book 1
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