## Homework #5

805377003
Posts: 97
Joined: Wed Sep 30, 2020 10:10 pm

### Homework #5

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

Can someone explain how to do this?

RDove_3G
Posts: 90
Joined: Wed Sep 30, 2020 9:48 pm

### Re: Homework #5

Hi, so for this problem you want to add together some of the reactions to create the given reaction. If you have to flip around a reaction (switch the products and reactants) the K value becomes 1/K because it is the reverse reaction. If you have to multiply all the coefficients of the reaction, the K value is raised to that power. Then you will have two reactions that add up to the given reaction (substances not in the final reaction should cancel out) and you multiply the K values of the combined reactions to get the K of the overall reaction.

jeffrey van 2I
Posts: 32
Joined: Wed Nov 25, 2020 12:21 am

### Re: Homework #5

Hi, I also struggled with this question, and I don't know if this is true for you, but for me the trouble was figuring out how to add two equations to form the overall equation. I think RDove explained the rules very well, but it might also help if we visualized how to combine two equations So let's say the overall equation is $A + B \rightleftharpoons D+E$
and the two equations you wish to add are $A+B\rightleftharpoons C+D$ and $C\rightleftharpoons E$
you would combine them like this:
Screenshot 2021-01-13 144506.png (7.21 KiB) Viewed 17 times

Because the element C is on the right side of the arrows in the first equation but on the left side in the second equation, you would "cancel it out". And to manipulate the equations and find your K value, you would follow the rules mentioned by RDove. Hopefully this is a helpful way to visualize combining chemical equations.