Enthalpy of SolutionAn example of enthalpy of reaction.

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Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl !

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl–

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl–

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 !

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl–

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

ZnSO4 !

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

ZnSO4 ! Zn2+ + SO42–

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

ZnSO4 ! Zn2+ + SO42– polyatomic Ions

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

ZnSO4 ! Zn2+ + SO42– Polyatomic Ions

CH3NH3NO3 !

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

ZnSO4 ! Zn2+ + SO42– Polyatomic Ions

CH3NH3NO3 ! CH3NH3+ + NO3

–

Calculating the Enthalpy of Solution

Determining the reaction from the information givenis required to obtain the enthalpy of solution. Forexample, complete the reaction for the solution of thefollowing:

Reaction Need to know

NaCl ! Na+ + Cl– Oxidation Number

FeCl2 ! Fe2+ + 2Cl– ...and Coefficients

ZnSO4 ! Zn2+ + SO42– Polyatomic Ions

CH3NH3NO3 ! CH3NH3+ + NO3

– Arrhenius Acid-base

Enthalpy of Solution

Here is an enthalpy calculation problem:

What is the molar enthalpy for the dissolution of Fe2S3?

Here is an enthalpy calculation problem:

What is the molar enthalpy for the dissolution of Fe2S3?

This is similar to all other enthalpy of reaction problems, butfor the student the question may be, “What is the reaction?”

Enthalpy of Solution

Enthalpy of Solution

Here is an enthalpy calculation problem:

What is the molar enthalpy for the dissolution of Fe2S3?

This is similar to all other enthalpy of reaction problems, butfor the student the question may be, “What is the reaction?”

At this point, you should know the polyatomic ions and howto figure oxidation numbers. If not, you already in trouble -go back and learn them. From the oxidation numbers, youshould know that here iron dissolves as Fe3+ ions and sulfuras S2! ions, thus the reaction would be:

Fe2S3 W 2Fe3+ + 3S2!

Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpyfor the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpyfor the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

This problem is handled the same as any other determinationof reaction enthalpy in chemistry. The first step is to look upthe enthalpy of formations of the products and reactants.

Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpyfor the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

This problem is handled the same as any other determinationof reaction enthalpy in chemistry. The first step is to look upthe enthalpy of formations of the products and reactants.

From the tables, the following values are obtained:

ΔH (Fe2S3) = !14.0 kJ mol-1

ΔH (Fe3+) = !48.5 kJ mol-1

ΔH (S2!) = +33.1 kJ mol-1»

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Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpy for the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

From the values from the table:

ΔH (Fe2S3) = !14.0 kJ mol-1

ΔH (Fe3+) = !48.5 kJ mol-1

ΔH (S2!) = +33.1 kJ mol-1

These values are to be used in the equation:ΔHrxn = 3ΔHproducts !3ΔHreactants

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Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpy for the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

From the values from the table:

ΔH (Fe2S3) = !14.0 kJ mol-1

ΔH (Fe3+) = !48.5 kJ mol-1

ΔH (S2!) = +33.1 kJ mol-1

The ΔHrxn may be calculate by substituting into the formula:ΔHrxn = 2ΔH (Fe3+) + 3ΔH (S2!) ! ΔH (Fe2S3)

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»f

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Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpy for the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

From the values from the table:

ΔH (Fe2S3) = !14.0 kJ mol-1

ΔH (Fe3+) = !48.5 kJ mol-1

ΔH (S2!) = +33.1 kJ mol-1

The ΔHrxn may be calculate by substituting into the formula:ΔHrxn = 2ΔH (Fe3+) + 3ΔH (S2!) ! ΔH (Fe2S3)Substituting:ΔHrxn = 2(-48.5 kJ mol-1 ) + 3(+33.1 kJ mol-1 ) + (!14.0 kJ mol-1 )»

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»f

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Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpy for the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

From the values from the table:

ΔH (Fe2S3) = !14.0 kJ mol-1

ΔH (Fe3+) = !48.5 kJ mol-1

ΔH (S2!) = +33.1 kJ mol-1

The ΔHrxn may be calculate by substituting into the formula:ΔHrxn = 2ΔH (Fe3+) + 3ΔH (S2!) ! ΔH (Fe2S3)Or:ΔHrxn = !11.7 kJ mol-1 »

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»f

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Enthalpy of Solution

So now the problem becomes: “What is the molar enthalpy for the following reaction:

Fe2S3 W 2Fe3+ + 3S2! ”

From the values from the table:

ΔH (Fe2S3) = !14.0 kJ mol-1

ΔH (Fe3+) = !48.5 kJ mol-1

ΔH (S2!) = +33.1 kJ mol-1

There is a side issue to note here. Notice that the ΔH for bothFe3+ and S2! do not have the subscript “f”. This is because theyare referenced to the ΔH for H+ and not to the elements. Thisdoes not affect the calculation, however.

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Calculating the Enthalpy of Solution

Using this information and the information fromprevious slides, calculate the following:

Example 2: Determine the enthalpy of solution forNaCl

Calculating the Enthalpy of Solution

Using this information and the information fromprevious slides, calculate the following:

Example 2: Determine the enthalpy of solution forNaCl

The reaction then is:

NaCl ! Na+ + Cl–

Calculating the Enthalpy of Solution

Using this information and the information fromprevious slides, calculate the following:

Example 2: Determine the enthalpy of solution forNaCl

The reaction then is:

NaCl ! Na+ + Cl–

ΔHsol = ΔHº(Na+) + ΔHº(Cl–) – ΔHº(NaCl)f

Calculating the Enthalpy of Solution

Using this information and the information fromprevious slides, calculate the following:

Example 2: Determine the enthalpy of solution forNaCl

The reaction then is:

NaCl ! Na+ + Cl–

ΔHsol = ΔHº(Na+) + ΔHº(Cl–) – ΔHº(NaCl)

ΔHsol = [(–240.1) + (–167.2) – (–411.54)]kJ mol–1

f

Calculating the Enthalpy of Solution

Using this information and the information fromprevious slides, calculate the following:

Example 2: Determine the enthalpy of solution forNaCl

The reaction then is:

NaCl ! Na+ + Cl–

ΔHsol = ΔHº(Na+) + ΔHº(Cl–) – ΔHº(NaCl)

ΔHsol = [(–240.1) + (–167.2) – (–411.54)]kJ mol–1

ΔHsol = 4.2 kJ mol–1

f

Enthalpy of SolutionAn example of enthalpy of reaction.

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