An important reaction for the conversion of natural gas to...

An important reaction for the conversion of natural gas to other useful hydrocarbons is the conversion of methane to ethane. $$ 2 \mathrm{CH}_{4}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2}(g) $$ In practice, this reaction is carried out in the presence of oxygen, which converts the hydrogen produced to water. $$ 2 \mathrm{CH}_{4}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2} \mathrm{O}(g) $$ Use bond enthalpies (Table 8.4) to estimate $\Delta H$ for these two reactions. Why is the conversion of methane to ethane more favorable when oxygen is used?

An important reaction for the conversion of natural gas to other useful hydrocarbons is the conversion of methane to ethane.
$$
2 \mathrm{CH}_{4}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2}(g)
$$
In practice, this reaction is carried out in the presence of oxygen, which converts the hydrogen produced to water.
$$
2 \mathrm{CH}_{4}(g)+\frac{1}{2} \mathrm{O}_{2}(g) \longrightarrow \mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{H}_{2} \mathrm{O}(g)
$$
Use bond enthalpies (Table 8.4) to estimate $\Delta H$ for these two reactions. Why is the conversion of methane to ethane more favorable when oxygen is used?

Key Concepts

Bond Enthalpies

Bond enthalpies refer to the amount of energy required to break a particular chemical bond in one mole of gaseous molecules. This concept is fundamental for estimating the energy changes in chemical reactions by comparing the bonds broken in the reactants with those formed in the products. Using average bond enthalpies allows scientists to predict whether a reaction will be endothermic or exothermic, even though there may be approximation errors due to the use of average values.

Reaction Enthalpy Estimation

Estimating the reaction enthalpy using bond enthalpies involves calculating the total energy required to break bonds in the reactants and subtracting the energy released when new bonds form in the products. This provides an overall ?H for the reaction. The method is widely applicable in thermochemistry for understanding energy changes during chemical transformations.

Role of Oxygen in Enhancing Reaction Favorability

The use of oxygen in the reaction converts the hydrogen produced from methane conversion into water. Water formation is highly exothermic due to the formation of strong O-H bonds, which releases additional energy. This extra energy release makes the overall reaction more thermodynamically favorable compared to the reaction without oxygen.

Transcript

00:01 We will be using bond enthalpies to compare two reactions.

00:07 Each of these reactions is the reaction of ethane to, or excuse me, of methane to ethane.

00:18 We are given two reactions.

00:19 The first reaction is to ch4, produces c2h6 plus h2, and all of these are gases.

00:41 My earbud fell out.

00:45 In reality, this reaction is carried out in the presence of oxygen.

00:56 Again, the first reaction and the reaction i'm writing right now are both provided in the problem.

01:20 And we're told to use bond enthopies from table 8 -4 in the textbook to estimate the change of enthalpy for these two reactions.

01:31 We're also going to compare why the code conversion of methane to ethane is more favorable when oxygen is used.

01:41 So in order to do this, i'm going to write down how many of each type of bonds there are.

01:47 I have four ch bonds here, and i have two methane for a total of eight c .h bonds.

02:00 Here, i have one carbon -carbon bond and six c -h bonds, and i have.

02:10 I have one hydrogen -hydrogen bond.

02:17 We have the same thing right here, same thing, so i have eight c -h bonds.

02:22 The same thing right here, so i have one, c, c, and six, c -h.

02:28 Here i have half an o2, and for the h -2o, i have two o -h bonds.

02:39 And looking at these, i have c -h bonds here and here.

02:50 I can see that i will have these cross out and i'll have two of these left, which means i'll have two ch bonds and i look up ch and i see that it is 413 kilojoules per mole...

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