[Pastulio6267]

So I've got a test tomorrow, and I under 90% of my study guide, but I can't for the life of me figure out the last 2 questions.



1)

The following has an equilibrium constant if 2.09 x 10^-3

2NOBr <--> 2NO+Br2

Decide whether the reaction is in equilibrium, or which direction the reaction should go if the reaction takes place in a 5L vessel. At equilibrium, there are 2.1 ATM of NOBr, 1.32 ATM NO, and 0.98 ATM Br2


I think this has something to do with the PV=K constant, but I'm not sure...

2)


The Kc of a reaction is 2.1x10^-4. If 6.7 g of methane were used to react with 1.23 moles of H2S in a 2 L container, how many grams of CS2 and H2 were produced if 0.217 moles of methane was presented at equilibrium

I tried solving this one using the ICE method, but my resulting moles never checked with the given Kc value. Thank you so much to whoever can explain this to me.

[Borek]

Decide whether the reaction is in equilibrium, or which direction the reaction should go if the reaction takes place in a 5L vessel. At equilibrium, there are 2.1 ATM of NOBr, 1.32 ATM NO, and 0.98 ATM Br2

Decide if the reaction is in equilibrium if it is at equilibrium? No idea what this question asks about.

I tried solving this one using the ICE method, but my resulting moles never checked with the given Kc value. Thank you so much to whoever can explain this to me.

Sorry, but we have no idea what you did. Could be an error in the ICE table, could be lousy math, could be a dying battery in your calculator. Everything. Hard to help.

[bstapes99]

for question 1, what kind of K is that? concentration or pressure?
if its concentration, we need to know temperature. if its pressure, you can do this.

[bstapes99]

sorry for the two posts, i was interrupted before i could finish my last one. Anyway,
Assuming K is K_p, you have to set up your pressure equilibrium equation k_p= P_NO²*P_Br2/P_NOBr²
Then, find the reaction quotient Q by plugging in your given values into the equation above. So Q_p=.98*1.32²/2.1²
You then take Q and decide: is the reaction at equilibrium? and if it isn't, which direction will the reaction go?

If K is really K_c, then you need a temperature at which the reaction is taking place. For example, if you assume a standard temperature os 293 K, then the problem becomes doable. Use the ideal gas equation PV=nRT with 5L, 293K, R=.0821, and the partial pressure of your gases to find moles of each. Convert those moles to concentrations, then use the same K equation, except with concentrations, to find Q, then answer the question.