close

Hess' Law of Heat Summation

 Hess’ Legislation of Heat Summation Essay

Hess'В LawВ ofВ HeatВ Summation

Hess'В LawВ statesВ that:

" TheВ enthalpyВ changeВ forВ anyВ reactionВ dependsВ onВ theВ productsВ andВ reactantsВ andВ isВ independentВ ofВ theВ pathwayВ orВ theВ numberВ ofВ stepsВ betweenВ theВ reactantВ andВ product". В

ESSENTIALLY: В В В Hess'В LawВ statesВ " theВ heatВ evolvedВ orВ absorbedВ inВ В В В aВ chemicalВ processВ isВ theВ sameВ whetherВ theВ processВ В В В takesВ placeВ inВ oneВ orВ inВ severalВ steps" В В В В В­В­> ThisВ isВ alsoВ knownВ asВ theВ " lawВ ofВ constantВ heatВ summation". В В В В В AllВ itВ meansВ isВ thatВ noВ matterВ howВ manyВ stepsВ theВ chemicalВ В В В reactionВ proceedsВ through, В theВ totalВ heatВ evolvedВ orВ absorbed В В В isВ theВ addedВ heatВ valuesВ ofВ eachВ stepВ andВ willВ alwaysВ be В В В aВ constantВ figureВ forВ thatВ process. В В В В ForВ example: В В В В WhenВ phosphoricВ acidВ (aВ triВ­hydrogenВ acid)В isВ neutralizedВ В В В withВ aВ base, В theВ hydrogensВ areВ neutralisedВ inВ 3В steps: В В В STEPВ 1: В В В H3P04В +В NaOHВ В­> В NaH2PO4В +В H2O В­givesВ XВ amountВ ofВ heatВ В В В STEPВ 2: В В В NaH2PO4В +В NaOHВ В­> В Na2HPO4В +В H2O В­givesВ YВ amountВ ofВ heat В В В STEPВ 3: В В В Na2PO4В +В NaOHВ В­> В Na3PO4В +H2O В­givesВ ZВ amountВ ofВ heat В В В Therefore, В theВ totalВ heatВ ofВ reactionВ (В В В Hrxn)В isВ equalВ to:

ThereВ areВ twoВ (2)В waysВ toВ calculateВ theВ heatВ ofВ reactionВ usingВ Hess'В Law:

1В­В В EquationВ MethodВ (AlgebraicВ Method) 2В­В В HeatВ ofВ FormationВ MethodВ (SummationВ Method)

EquationВ (Algebraic)В Method

Strategy: В В В В­addВ equationsВ forВ reactionsВ withВ knownВ enthalpies В В В В soВ thatВ theirВ netВ resultВ isВ theВ desiredВ reaction

SampleВ ProblemВ 1: UseВ theВ equationsВ belowВ toВ determineВ theВ enthalpyВ ofВ reaction forВ theВ decompositionВ ofВ hydrogenВ peroxide:

H2O2(l)В В В В В В В В В H2O(l)В В В В +В В В В 1/2В O2(g)

TheВ equationsВ are: 1В­В В В В H2(g)В В В +В В В O2(g)В В В В В В В H2O2(l)В В В 2В­В В В В H2(g)В В В +В В В 1/2В O2(g)В В В В В В H2O(l)

HfВ =В В­188В kJ

HfВ =В В­286В kJ

Solution:

SampleВ ProblemВ 2: UseВ theВ followingВ equations: 1В­В В В В 1/2В N2(g)В В В +В В В 3/2В H2(g)В В В В В В В NH3(g) 2В­В В В В 1/2В N2(g)В В В +В В В O2(g)В В В В В NO2(g) 3В­В В В В H2(g)В В В +В В В 1/2В O2(g)В В В В В H2O(g)

HfВ =В В­46. 0В kJ

HfВ =В +34. 0В kJ HfВ =В В­242. 0В kJ...

 Tour Guide Article

Tour Guide Article

A tour guide (or tourist guide) provides assistance, information and cultural, traditional and modern day heritage interpretation to people about organized tours, individual clientele, educational organizations, at religious and historic…...

Read
 Organ Gift Essay

Organ Gift Essay

Appendage Donation Arlene B HCA322: The spring 30, 2012 Organ Donation Organ and tissue gift can help to save the lives of…...

Read