Easy Multiple Choice Question

[boysenberry]

Hi there! 

I'm going through unit 4 chemistry in preparation for next year. Below is a multiple choice question on reaction rates and equilibrium. Could somebody please tell me what the answer is briefly detailing why. I know what the answer is and I'm more interested in the reason why the answer is what it is. I am aware this is not difficult question. Anyway, any help will be appreciated. 

Questions 5, 6 and 7 refer to the following information.
The reaction represented by the equation:



has an equilibrium constant, K of 1.58 at 990°C. In an experiment, the concentrations of these four substances were measured at a particular time. The values obtained are shown below:






5) Which of the following statements is true of this reaction at this time?
A) There is a net forward reaction.
B) There is a net backward reaction.
C) The rate of the backward reaction is faster than the rate of the forward reaction.
D) The reaction is at equilibrium.

[kendraaaaa]

At first glance of this question, it gives you the concentrations of the particles in this system at a particular time. Hence, the next step is to find the concentration fraction at this point in time, which is:

Q = [CO][H20] / [CO2][H2]
   = (0.0027)*(0.0025) / (0.00208)*(0.00221)
   = 1.47

From this we see that the Q value for the system at this point in time is less than the K. Thus, a) is correct since the system needs to increase the concentration of the products to get back to equilibrium.




I hope 3-4 weeks since the chem exam hasn't wiped knowledge from my brain....haha.

[boysenberry]

At first glance of this question, it gives you the concentrations of the particles in this system at a particular time. Hence, the next step is to find the concentration fraction at this point in time, which is:

Q = [CO][H20] / [CO2][H2]
   = (0.0027)*(0.0025) / (0.00208)*(0.00221)
   = 1.47

Ah, yes. That's what I did before. Though I wasn't entirely sure what the the value of Q meant and what that implied as its value being lower than the equilibrium constant.

[kendraaaaa]

There you go. Also, with questions like these there can be some variations. For instance, if it told you that the temperature was 700 degrees at that instantaneous point. It could ask you whether the reaction is exo/endothermic. You'd answer endothermic since a lower temperature has given a lower K value.

It's good to try to cover all bases when you do a question, to get a thorough understanding. Just one last note, you really should be looking at Unit 3 not Unit 4 at this point in time.

[boysenberry]

Just one last note, you really should be looking at Unit 3 not Unit 4 at this point in time.

I've read the theory unit 3 (haven't done any questions) and this part of unit 4 seems most relevant to unit 2 which I've just completed.

[crappy]

Just one last note, you really should be looking at Unit 3 not Unit 4 at this point in time.

I've read the theory unit 3 (haven't done any questions) and this part of unit 4 seems most relevant to unit 2 which I've just completed.

yeah thats fine, but unit 3 is just packed with so much bullshit, its best to get a head start now and attempt questions. Unit 4 is much more relaxing, its not very stressful and just takes some time to understand the concepts.