Sapling HW 1 #5

[Janna Shakiba]

Consider the reaction of NH3 and I2 to give N2 and HI.

2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g) K

Using two or more of the given equations, determine the equilibrium constant, K, for the reaction of NH3 with I2.

H2(g)+I2(g)↽−−⇀2HI(g) Ka=160
I2(g)↽−−⇀2I(g) Kb=2.1×10−3
N2(g)+3H2(g)↽−−⇀2NH3(g) Kc=3.6×10−2
H2(g)+Cl2(g)↽−−⇀2HCl(g) Kd=4.0×1018

[Janelle Gokim 3B]

Essentially for this problem, you will be making use of Hess's law and selecting certain chemical reactions that can add up to the given reaction at hand. This can involve manipulating the reactions below, whether that's reversing it, or simply multiplying it by a coefficient. It is important to note that when you make these changes, K needs to be modified accordingly. If you reverse the reaction, K becomes 1/K and if you multiply the reaction by a coefficient n, K becomes K^n. Once you have the correct K values and reaction, to find the overall K value, you multiply the equilibrium constants of all intermediate/added reactions. Looking at this problem below, I believe the first and third reactions will be used.

[Karen Zheng_2K]

^ I got the same answer, 1st and 3rd reactions!

[Alex Benson]

What I did was multiply the first reaction and the inverse of the third reaction by their molar ratios!

[Juliana Rosales 1H]

Thanks for asking this question! I was having trouble with this question and I made the exact same mistake lol.

[IreneSeo3F]

You would use first and third reactions.
Cube Ka because you multiply the coefficients by 3 to get 3H2+3I2->6HI. Then take the inverse of Kc because you need the inverse reaction to get 2NH3->N2+3H2. Then you multiply those values to determine final K.
Hope this helped!

[David Liu 1E]

make sure to factor/remember to use inverse reactions for these types of questions! It was something I forgot about when I first did it too

[505578531]

Thank you for asking I had this question as well, and would have gotten it wrong lol, my money was the second and third equation.

[Ranen_Chang_2G]

It helps to look at what you need to cancel out from both the reactants and products side. By manipulating the equations by reversing them or multiplying them by a multiple, you can see what you need.