You are Here: Home >< A-levels

Equilibrium Constants from moles

Announcements Posted on
Would YOU be put off a uni with a high crime rate? First 50 to have their say get a £5 Amazon voucher! 27-10-2016
1. Any help is appreciated!

For the equilibrium:
H2(g) + I2(g) = 2HI (g)

When 0.5 mol of H2 (g) and 0.18 mol of I2 (g) were heated to 500C the equilibrium mixture contained 0.01 mol of I2 (g). Calculate the equilibrium constant Kc for this reaction.

So far I think I'm half there:

H2 + I2 = 2HI
Initial moles: 0.5 0.18 0
At equil: 0.01
Equil conc: 0.33/V 0.01/V 0.34/V

From this I determined that 0.17 mol of Iodine was being used so therefore 0.17 mol of Hydrogen were used to give the 2HI 0.34 mol

From this Kc = [HI]2 / [H2] [I2]
Kc = 0.34/V / 0.33/V . 0.01/V

Any advice to where the theory went wrong or another method of calculating the Kc is appreciated. Thanks in advance!
2. (Original post by RedPixieDust)
Any help is appreciated!

For the equilibrium:
H2(g) + I2(g) = 2HI (g)

When 0.5 mol of H2 (g) and 0.18 mol of I2 (g) were heated to 500C the equilibrium mixture contained 0.01 mol of I2 (g). Calculate the equilibrium constant Kc for this reaction.

So far I think I'm half there:

H2 + I2 = 2HI
Initial moles: 0.5 0.18 0
At equil: 0.01
Equil conc: 0.33/V 0.01/V 0.34/V

From this I determined that 0.17 mol of Iodine was being used so therefore 0.17 mol of Hydrogen were used to give the 2HI 0.34 mol

From this Kc = [HI]2 / [H2] [I2]
Kc = 0.34/V / 0.33/V . 0.01/V

Any advice to where the theory went wrong or another method of calculating the Kc is appreciated. Thanks in advance!
The first bit looks right to me, but did you remember to square the concentration of [HI] to get Kc? Also, don't forget the units

Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: May 18, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

Poll

All the essentials

Student life: what to expect

What it's really like going to uni

Essay expert

Learn to write like a pro with our ultimate essay guide.

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Resources by subject

Everything from mind maps to class notes.

Study tips from A* students

Students who got top grades in their A-levels share their secrets