# HELP! Chemistry emergency :( (1 Viewer)

#### lucywills24

##### New Member
So I haven’t studied for chem all summer holidays and I have forgotten so much content, so I have to start back at mod 5. Can anyone please help me with this question, the answer is D but I can’t figure out why. Thanks

#### jazz519

##### Moderator
Moderator
So I haven’t studied for chem all summer holidays and I have forgotten so much content, so I have to start back at mod 5. Can anyone please help me with this question, the answer is D but I can’t figure out why. Thanks

View attachment 34828
For the 1st reaction:

K = [O2] [HCL]^4 / [Cl2]^2 [H2O]^2
4.0 x 10^(-4) = [O2] [HCL]^4 / [Cl2]^2 [H2O]^2

For the 2nd reaction:
K = [Cl2] [H2O] / [O2]^(1/2) [HCL]^2

We need to change the first expression into the 2nd one. This would involve flipping the fraction i.e.

1 / (4x10^-4) = [Cl2]^2 [H2O]^2 / [O2] [HCL]^4

and then taking a square root

sqrt( 1 / 4 x 10^-4) = [Cl2] [H2O] / [O2]^(1/2) [HCL]^2

Sub that into a calculator and it will give the answer

#### lucywills24

##### New Member
For the 1st reaction:

K = [O2] [HCL]^4 / [Cl2]^2 [H2O]^2
4.0 x 10^(-4) = [O2] [HCL]^4 / [Cl2]^2 [H2O]^2

For the 2nd reaction:
K = [Cl2] [H2O] / [O2]^(1/2) [HCL]^2

We need to change the first expression into the 2nd one. This would involve flipping the fraction i.e.

1 / (4x10^-4) = [Cl2]^2 [H2O]^2 / [O2] [HCL]^4

and then taking a square root

sqrt( 1 / 4 x 10^-4) = [Cl2] [H2O] / [O2]^(1/2) [HCL]^2

Sub that into a calculator and it will give the answer
Thank you so much that really helped, I appreciate your response! I was just wondering, why do you need to square root for the answer?

#### jazz519

##### Moderator
Moderator
Thank you so much that really helped, I appreciate your response! I was just wondering, why do you need to square root for the answer?
Because if you at the terms like [H2O]^2 which changes to [H2O] the only way to get rid of the power on the H2O is by taking a square root