Sapling HW 1 #5

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Janna Shakiba
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Joined: Wed Sep 30, 2020 10:02 pm

Sapling HW 1 #5

Postby Janna Shakiba » Sun Jan 10, 2021 6:58 pm

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
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Re: Sapling HW 1 #5

Postby Janelle Gokim 3B » Sun Jan 10, 2021 7:02 pm

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
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Re: Sapling HW 1 #5

Postby Karen Zheng_2K » Sun Jan 10, 2021 7:22 pm

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

Alex Benson
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Re: Sapling HW 1 #5

Postby Alex Benson » Sun Jan 10, 2021 8:55 pm

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

Juliana Rosales 1H
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Re: Sapling HW 1 #5

Postby Juliana Rosales 1H » Sun Jan 10, 2021 9:50 pm

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

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Re: Sapling HW 1 #5

Postby IreneSeo3F » Sun Jan 10, 2021 10:40 pm

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
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Re: Sapling HW 1 #5

Postby David Liu 1E » Sun Jan 10, 2021 11:00 pm

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

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Re: Sapling HW 1 #5

Postby 505578531 » Sun Jan 10, 2021 11:14 pm

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.

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Joined: Wed Nov 25, 2020 12:21 am

Re: Sapling HW 1 #5

Postby Ranen_Chang_2G » Sun Jan 10, 2021 11:33 pm

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.

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