TBR Equilibrium Question

[salsasunrise123]

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Hello, So I am getting rocked by TBR gen chem equilibrium passages and was hoping someone could help explain some stuff to me. My questions are below:

1) 2 CO(g) + Q2(g) -> 2 C02(g)

According to Reaction 1, compressing the reaction
vessel leads to which ofthe following?
A. An increase in the partial pressure ofC02(g)
B. An increase in the moles of 02(g)
C. An increase in the mole fraction ofCO(g)
D. An increase in the equilibrium constant

* I don't get why answer is not A since decreasing volume should shift to side with more moles.

2) Based on the following reaction (use reaction above), the addition of
Ca(OH)2(aq) to Reaction 1 at equilibrium results in
which ofthe following?
Ca(OH)2(aq) + C02(g) -> CaC03(s) + H20(1)
A. No change in the moles of C02(g).
B. A decrease in the concentration of02(g).
C. An increase in partial pressure ofCO(g).
D. An increase in the total pressure.

*Solution says the CaCO3 replaces CO2 in original reaction, which I do not get at all??? What am I missing? Im lost

3) H2(g) + Br2(l) -> 2 HBr(g)
Which of the following starting conditions results in
the GREATEST amount ofH2(g) at equilibrium?
A. 0.80 atm. H2(g) and 20 g Br2(l)
B. 1.00 atm. H2(g) and 20 g Br2(l)
C. 0.80 atm. H2(g) and 30 g Br2(l)
D. 1.00 atm. HBr(g) and 30 g Br2(l)

*Answer is B but I don't get how they arrive at it. I know that it can't be A or C, but don't know how to eliminate D.

Thank you so much for the help! It means a lot!

 

[salsasunrise123]

bump. Please help.

 

[dudewheresmymd]

1)

bump. Please help.

not very clear with these questions can you provide chapter or page number?

 

[TheUPSIDEdown]

First off, the first question is A... but increasing pressure / decreasing volume shifts to the side with less moles, not more.

As for the second question, your Kp value is considerably larger than one. The equation they've given you assumes Kp, therefore, only CO2 with negligible amounts of your initial reactants are left. Then they added Ca(OH)2, which drives the CO2 to new products. Therefore, the equilibrium of the initial reaction will now favor even greater the production of CO2 because CO2 is being used up with Ca(OH)2. Therefore, the answer is that the O2 (the initial reactant) is decreasing.

For the third question, choosing between the two answers is easy. Br2 is on the same side as H2, so in order to attain the most H2 at eq, you need the smallest amount of Br2 and the largest amount of H2, because the HBr can only be formed with both, so make Br2 the limiting reagent aka the smallest amount will allow for that.

Hope this helps.

 

[DrknoSDN]

To answer:

"Solution says the CaCO3 replaces CO2 in original reaction, which I do not get at all??? What am I missing? Im lost"

It means that if you wrote out the two reactions as step 1 and step 2... then the Co2 product from step 1 becomes a reactant in step 2 and disappears..
So the overall reaction (3rd line is simplified by replacing the term CO2 with CaCO3

Step 1: 2 CO(g) + Q2(g) -> 2 C02(g)
Step 2: Ca(OH)2(aq) + C02(g) -> CaC03(s) + H20(1)
-----------------------------------------
Overall: 2 CO(g) + Q2(g) + Ca(OH)2(aq) -> CaC03(s) + H20(1)



This also explains how if you begin forming CaCO3 from CO2 in step 2, the CO2 concentration will decrease causing a right shift in step 1, thereby lowering O2 concentration.

 

[SweetBurger]

Sorry i know this is some what of an old thread, but no one answered your third question so i will attempt to.

3) H2(g) + Br2(l) -> 2 HBr(g)
Which of the following starting conditions results in
the GREATEST amount ofH2(g) at equilibrium?
A. 0.80 atm. H2(g) and 20 g Br2(l)
*B. 1.00 atm. H2(g) and 20 g Br2(l)
C. 0.80 atm. H2(g) and 30 g Br2(l)
D. 1.00 atm. HBr(g) and 30 g Br2(l)
Alright think of Le chatelier's principle if you increase the amount of substance on the left side of the reaction, the reaction will proceed to the right. BUT if you want to have the greatest amount of H2 at equilibrium YOU DO NOT WANT TO INCREASE THE REACTANTS.....AT ALL in this case Br2. So 30gof Br2 would cause a greater decrease in H2 as more of it would be forced to react to reachieve equilibrium. This is why the answer is B because 20g of Br2 will have much less of an affect on the foward reaction as 30g of Br2 would.