Using the standard enthalpy of formation data in Appendix G,...

Key Concepts

Standard Enthalpy of Formation

This concept refers to the heat change that occurs when one mole of a compound is formed from its constituent elements in their standard states. It is essential in thermochemistry for comparing the energies of compounds and for deducing the overall energy balance of reactions, which can indirectly provide insights into the strength of chemical bonds within the molecules.

Bond Energy

Bond energy, or bond dissociation energy, is the amount of energy required to break a specific chemical bond in a molecule. It serves as a direct measure of bond strength, and comparing bond energies allows chemists to determine which bonds are stronger; higher bond energy indicates a stronger bond.

Hess's Law

Hess's Law states that the overall enthalpy change for a chemical reaction is the same, regardless of the number of steps or the pathway taken. This principle allows the calculation of reaction enthalpies by summing the standard enthalpies of formation of products and reactants, thereby facilitating the comparison of bond strengths indirectly through energy changes.

Transcript

00:01 Today, in this video we are going to determine which bond is stronger between the s to f bond in sf4 gases or in sf6 gases.

00:12 We're using standard enthalpy of formation data.

00:15 So i've extracted the standard enthalpy of formation data for sulfur gas, fluorine gas, sf4 gas and sf6 gas.

00:24 So in order to find out which bond is stronger, we need to calculate the bond in energy.

00:31 And to start off, we need to write down the chemical equations.

00:37 So let's start off with sf4.

00:41 S .f.

00:42 4 gas will dissociate 218, sulfur, solid plus 2 .f2 gas.

01:07 This would be our first entropy change of form.

01:10 Our first enthalpy.

01:12 And the second one is now to deal with the reactants.

01:19 So we have got 1 over 8 sulfur, which is in the solid state, forming sulfur in the gaseous state.

01:34 This will be our second enthalpy.

01:45 The third equation is now for fluorine.

01:54 Oh, sorry, this is supposed to be three.

02:03 No, my apologies, that's two.

02:05 So now for fluorine, it's two fluorine atoms, so there's two moles.

02:11 So it's two moles of fluorine gas.

02:26 To monotomic atom d times 4 and this is our third enthalpy change.

02:39 So to calculate the bond energy, we subtract the entropy change of formation of sf4 from the total bond energies for the reactants.

02:58 Bond energy for sf4 will be equal to 278.

03:08 0 .81 kilojouze per mole for sulfur plus there are four moles four times plus four times 79 .4 kilojoules minus 728 .4 for sf4.

04:07 You see there it is and this will give us a total of 1 ,324 .84 kilojoules per more.

04:28 Now that is the bond energy for the entire compound.

04:32 To calculate the bond energy for the s to f bond, we divide 1 ,324 .84 by 4 because there are 4 bonds...

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