The conversion of natural gas, which is mostly methane, into products that contain two or more carbon atoms, such as ethane (C₂H₆), is a very important industrial chemical process. In principle, methane can be converted into ethane and hydrogen: 2 CH₄(g) → C₂H₆(g) + H₂(g) In practice, this reaction is carried out in the presence of oxygen: 2 CH₄(g) + 1/2 O₂(g) → C₂H₆(g) + H₂O(g) (c) Explain how the preceding reactions are an example of driving a nonspontaneous reaction, as discussed in the 'Chemistry and Life' box in Section 19.7.

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Welcome back everyone in this example we have glutamate converted to glutamine. As shown below. From the reaction where we have glutamate reacting with ammonia to form glutamine. Were given the standard gibbs free energy change as positive 14.2 kg joules per mole. And we're told that this reaction occurs in the presence of a teepee where we have a T. P. Which forms ADP and inorganic phosphate PCB. We're told that this reaction occurs at a standard gibbs free energy change of negative 30.5 kg joules per mole. And in the next step they add the reactant of both reactions as well as the products of both reactions together. To give us one whole equation here and then we add our standard gibbs free energy changes together to give the value negative 16.3 kg Permal. We need to figure out how this reaction is an example of driving a non spontaneous reaction. Now we want to make note of the values of our standard gibbs free energy changes for each of the reactions. In the first reaction we have a positive value, recall that when we have a positive delta G. That means our reaction is non spontaneous and requires an energy input to occur. I'm sorry, that should have a hyphen for non spontaneous. Whereas when we look at our second reaction, we have a gibbs free energy. Standard gibbs free energy of this value here which is also which is on the contrary negative. And recall that when we have a negative value for delta G. That means our reaction is spontaneous. So we don't need an energy input for the reaction to occur. Now when we combine the reactant and products of both of these reactions and when we add up our delta G. S. We yield this third standard entropy or standard Gibbs free energy change of negative 16.3 kg per mole. And because it's a negative value yet again to produce our products spontaneously because it's a negative gibbs free energy change. And so we don't need an energy input. Sorry. So I will say products formed spontaneously. So to explain for why this reaction is an example of a of driving a non spontaneous reaction. We can say that the conversion of glutamate to glutamine in our first reaction is coupled with the conversion of A. T. P. To A. D. P. Sorry, that should be an A. In our secondary action. We don't need to write that part out. But that comes from our second reaction and thus overall Giving a 3rd reaction that produces products, sorry, produces products spontaneously. And so to shorten this summary, we can say that a non spontaneous reaction, which was our first reaction is coupled with a spontaneous reaction to produce products spontaneously. And this simplified statement here is going to be our final answer. To complete this example. I hope everything I reviewed was clear. This was just a matter of analyzing the positive or negative magnitudes of our standard gibbs free energy changes for each reaction. And if you do have any questions, just leave them down below, so I'll see everyone in the next practice video.

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Key Concepts

Spontaneity of Reactions

Reaction Coupling

Role of Oxygen in Combustion