I have this question as a review question:

The reaction N2(g)+3H2(g)<-->2NH3(g) begins with 1.15 M N2 and 1.36 M H2. At equilibrium, the concentration of NH3 is 0.78 M.

Determine the extent of reaction.

The answer is supposed to be 86 but I don't know how

Here is a site you can read. I don't think 86 is the right answer either.

I think closer to 0.39 (39%)
https://en.wikipedia.org/wiki/Extent_of_reaction

ok thanks!

To determine the extent of the reaction, we need to compare the initial concentrations with the equilibrium concentration of NH3.

First, let's write down the balanced chemical equation for the reaction:

N2(g) + 3H2(g) ⇌ 2NH3(g)

The stoichiometry of the reaction shows that for every 1 mole of N2 that reacts, 2 moles of NH3 are formed. Thus, the extent of reaction, often denoted as ξ (xi), represents how much the reaction has progressed in terms of the number of moles of reactants and products that have been converted.

Let's assume that the extent of reaction is ξ moles of N2 being converted to ξ * 2 moles of NH3.

At the start, we have 1.15 M N2. After the reaction has reached equilibrium, the concentration of NH3 is given as 0.78 M. According to the stoichiometry, the concentration of NH3 should be twice the concentration of N2 that is consumed.

Therefore, using the equation:
2NH3(g) = 0.78 M

Since the stoichiometric coefficient of NH3 is 2, this means that the concentration of N2 consumed is:
ξ * 1.15 M = 0.78 M

Solving for ξ:
ξ = 0.78 M / 1.15 M

ξ ≈ 0.6783

Since ξ represents the amount of N2 reacted, the extent of reaction is approximately 0.6783 moles of N2 being converted to 0.6783 * 2 = 1.3566 moles of NH3.

To express the extent of reaction as a percentage, we can divide the number of moles of N2 reacted by the initial number of moles of N2 and multiply by 100:
(0.6783 moles N2 / 1.15 moles N2) * 100 = 58.93%

However, it seems that the given answer is 86. To obtain this result, it is possible that additional information or calculations are required. Please review the question or share more details provided in the problem to assist further.