Enthalpy Change Problems

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Prepared by Lawrence KokVideo Tutorial on Energetics, Hesss Law, Enthalpy of Formation and Combustion in Energetics.

Video on Energetics and Enthalpy CalculationEnthalpy of reaction using combustion dataEnthalpy of reaction using combustion dataEnthalpy of reaction using formation dataEnthalpy of reaction using formation data

Basic Rules for H Enthalpy changes calculationsTotal amt energy released/absorbed is to number of moles of reactantsH for reverse reaction is EQUAL in magnitude but opposite in sign to H forwardStandard condition for measuring STANDARD ENTHALPY CHANGE, H1234Unit for H is KJ mol -1

Temp and Heat Enthalpy change H measured using a calorimeterSpecific heat capacity for a substance water ( 4.18J g-1K-1)567Basic Rules for H Enthalpy changes calculationsStandard Enthalpy Change of Formation for a reaction, H f

Standard Enthalpy Change of reaction, H fNotes on H f

H f = Amt of energy absorbed or released when ONE mole of compound formed fromIts standard state from its constituents in their standard statesEx : NaCI (s) + 1/2CI2 (g) NaCI (s)

Standard Enthalpy Change of reaction, H f

H f = Amt of energy absorbed or released when ONE mole of compound formed fromIts standard state from its constituents in their standard statesEx : NaCI (s) + 1/2CI2 (g) NaCI (s) Calculate the H ,enthalpy change for the reaction below 4 CH3NHNH2 + 5 N2O4 4CO2 + 12 H2O + 9N2Ex 1

1StepsCalculate the H ,enthalpy change for the reaction below 4 CH3NHNH2 + 5 N2O4 4CO2 + 12 H2O + 9N2

Ex 1

Formation of products dataFormation of reactants data12Steps

Calculate the H ,enthalpy change for the reaction below 4 CH3NHNH2 + 5 N2O4 4CO2 + 12 H2O + 9N2Ans

Calculate the H ,enthalpy change for the reaction below Formation data4 CH3NHNH2 + 5 N2O4 4CO2 + 12 H2O + 9N2AnsAnsNH4NO3 N2O + 2 H2O using energy cycle diagram

Ex 2Calculate the H ,enthalpy change for the reaction below NH4NO3 N2O + 2 H2O using energy cycle diagram

Ex 2Calculate the H ,enthalpy change for the reaction below AnsFormation dataNH4NO3 N2O + 2 H2O using energy level diagramEx 2Calculate the H ,enthalpy change for the reaction below

NH4NO3 N2O + 2 H2O using energy level diagram

Ex 2Calculate the H ,enthalpy change for the reaction below AnsFormation data

C2H6 + 7/2O2 2CO2 + 3 H2O using energy cycle diagram

Calculate the H ,enthalpy change for the reaction below Ex 3C2H6 + 7/2O2 2CO2 + 3 H2O using energy cycle diagram

Calculate the H ,enthalpy change for the reaction below Ex 3AnsC2H6 + 7/2O2 2CO2 + 3 H2O using energy level diagram Calculate the H ,enthalpy change for the reaction below Ex 3

C2H6 + 7/2O2 2CO2 + 3 H2O using energy level diagram

Calculate the H ,enthalpy change for the reaction below Ex 3Ans

C2H4 + H2 C2H6 Calculate the H ,enthalpy change for the reaction below Ex 4

C2H4 + H2 C2H6

Calculate the H ,enthalpy change for the reaction below Ex 4AnsEnergy Cycle diagram

C2H4 + H2 C2H6

Calculate the H ,enthalpy change for the reaction below Ex 4AnsEnergy Cycle diagram or Energy Level DiagramAnswer the same = -137kJmol-1Write balanced equation and calculate the H for the following reactionsZinc + Chlorine forming zinc chloride

b) Hydrogen sulfide + sulfur dioxide forming sulfur and water

c) Lead (II) nitrate decomposing to lead (II) oxide, nitrogen dioxide and oxygen

Ex 5Write balanced equation and calculate the H for the following reactionsZinc + Chlorine forming zinc chloride

b) Hydrogen sulfide + sulfur dioxide forming sulfur and water

c) Lead (II) nitrate decomposing to lead (II) oxide, nitrogen dioxide and oxygen

Ex 4Standard Enthalpy Change of combustion, H c

Standard Enthalpy Change of combustion, H cNotes on combustion

H c = Amt of energy released when ONE mole of substance completely burnt in OXYGEN under standard conditions

2 C + 3H2 C2H6 Calculate the H ,enthalpy change for the reaction below Ex 1Using Energy Cycle Diagram

2 C + 3H2 C2H6 Calculate the H ,enthalpy change for the reaction below Ex 1AnsUsing Energy Cycle Diagram

Calculate the H ,enthalpy change for the reaction below 2 C + 2H2 C2H4 Ex 2Using Energy Cycle Diagram1st method

Calculate the H ,enthalpy change for the reaction below 2 C + 2H2 C2H4

Ex 2

AnsUsing Energy Cycle Diagram1st method

Calculate the H ,enthalpy change for the reaction below 2 C + 2H2 C2H4 Ex 2Using Energy Level Diagram2nd method

Calculate the H ,enthalpy change for the reaction below 2 C + 2H2 C2H4 Ex 2AnsUsing Energy Level Diagram2nd method

2 C + 3H2 + 1/2O2 C2H5OH Calculate the H ,enthalpy change for the reaction below Ex 3Using Energy Cycle Diagram1st method

2 C + 3H2 + 1/2O2 C2H5OH

Calculate the H ,enthalpy change for the reaction below Ex 3Using Energy Cycle DiagramAns1st method

Calculate the H ,enthalpy change for the reaction below Ex 3Using Energy Level Diagram2 C + 3H2 + 1/2O2 C2H5OH 2nd method

Calculate the H ,enthalpy change for the reaction below Ex 3Using Energy Level Diagram2 C + 3H2 + 1/2O2 C2H5OH Ans2nd method2 C + 3H2 + 1/2O2 C2H5OH

Calculate the H ,enthalpy change for the reaction below Ex 41st method, using combustion dataTWO methods

Combustion data

2 C + 3H2 + 1/2O2 C2H5OH

Calculate the H ,enthalpy change for the reaction below Ex 4Ans1st method, using combustion dataTWO methodsCombustion data

Calculate the H ,enthalpy change for the reaction below Ex 42nd method, using formation data2 C + 3H2 + 1/2O2 C2H5OH

Formation data

Calculate the H ,enthalpy change for the reaction below Ex 42nd method, using formation data2 C + 3H2 + 1/2O2 C2H5OH AnsFormation data

3C2H2 C6H6

Calculate the H ,enthalpy change for the reaction below Ex 5Using combustion dataCombustion data

3C2H2 C6H6

Calculate the H ,enthalpy change for the reaction below Ex 5Using combustion data

AnsCombustion dataCalculate H c ,enthalpy change for combustion of propene shown below3CH2 =CHCH3 + 9/2O2 3CO2 + 3H2O6

Ex 6Using combustion /formation dataCalculate H c ,enthalpy change for combustion of propene shown below3CH2 =CHCH3 + 9/2O2 3CO2 + 3H2O6

Ex 6Using combustion /formation data

Ans

C2H4 + H2 C2H6

Calculate the H ,enthalpy change for the reaction below Ex 7Using Energy Cycle DiagramUsing Energy Level Diagram

Answer the same = -137kJmol-1

Video on Energetics and Enthalpy CalculationUsing equation method to solve HUsing equation method to solve HUsing formation enthalpy to solve H (Khan Academy)Concept on enthalpy, H (Khan Academy)Acknowledgements

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Prepared by Lawrence Kok

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