Forum Rules: Read This Before Posting


Topic: Interpreting reaction rate graphs of a system re-establishing equilibrium  (Read 1144 times)

0 Members and 1 Guest are viewing this topic.

Offline carlsone

  • Regular Member
  • ***
  • Posts: 10
  • Mole Snacks: +0/-1
Hi everyone, would appreciate your help with this multi-choice question. Apparently the answer is c.
Consider the following equilibrium
2ClF3(g)  ::equil:: 3F2(g) + Cl2(g) ∆H = negative
The system is initially at equilibrium. At time t1, the temperature of the system was increased. Which of the following best represents the changes in the forward and reverse reaction rates until equilibrium is re-established at t2?

My take: Both rates would initially increase, then the reverse would increase to remove the 'imposed' heat from the system. This heat would be used to form bonds and therefore decrease the temperature. So the forward rate would decrease. But that matches with A not C.  What am I missing?
« Last Edit: February 12, 2018, 06:55:42 AM by Arkcon »

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1532
  • Mole Snacks: +219/-9
Re: Interpreting reaction rate graphs of a system re-establishing equilibrium
« Reply #1 on: February 12, 2018, 08:46:33 AM »
Chemicals don't know Le Chatelier's principle. They don't know they're supposed to (e.g.) "remove imposed heat" from a system. And they can't do that by forming bonds. Forming bonds releases heat. LCP arises as a result of things behaving in their natural way, so approach it that way.
What happens to the forward and reverse rate constants when the temperature is increased?
What happens to the rates of the forward and reverse reactions when the temperature is increased?
What happens to the concentrations of reactants and products as a result?
What effect does this have on the forward and reverse reaction rates?
What must be true about the reaction rates at the new equilibrium?

Offline carlsone

  • Regular Member
  • ***
  • Posts: 10
  • Mole Snacks: +0/-1
Re: Interpreting reaction rate graphs of a system re-establishing equilibrium
« Reply #2 on: February 12, 2018, 07:07:40 PM »
Following what you have said: Increasing temperature will increase the rate of both the reverse and forward reaction. The greater number of particles on the right hand side will result in more frequent collision and a greater in concentration of Chlorine. To re-establish equilibrium the Chlorine is up at a higher rate, hence the rate of the forward reaction increase and the rate of the reverse slows down.

The above probably needs some adjusting, would really appreciate it. But how do I reconcile this with LCP isn't it contrary to what I have written? Thanks for the input by the way.

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 1532
  • Mole Snacks: +219/-9
Re: Interpreting reaction rate graphs of a system re-establishing equilibrium
« Reply #3 on: February 14, 2018, 07:21:11 AM »
Try answering each of my questions, specifically and in order. And remember, nothing is "trying" to absorb heat or re-establish equilibrium. That is a result, not a purpose.

Sponsored Links