With Exam 2 next Tuesday, identify one topic that is causing you issues from Chapter 13 or Chapter 14. The next person should address the issue and then list their own issue.
For example: In a given mechanism, how would I know which step is the slow step if they are not identified but the experimental rate law is?
To be completely honest, Chapter 13 went completely over my head. My question would be how to tell if its zero, first or second order. Also I don't understand which elementary steps to use and when, and how to verify the 3rd criteria for a mechanism. I've read over my notes countless times, but nothing is clicking.
ReplyDeleteTo answer Ms. Nguyen's question: when the experimental rate law is given write the rate law for each of the steps using the reactant part of the equation. Compare that to the experimental rate law. If none of the rate laws match the experimental rate law then a rate law that uses an intermediate is probably the slow step. More work needs to be done to confirm that though.
ReplyDeleteTo answer Taylor's question: honestly try doing mastering chemistry and looking up videos maybe to explain things or go to Ms. Nguyen's office hours. Because I can try to explain all those things to you but if reading the notes isn't helping you, I"m pretty positive my explanation will only confuse you further. For the zero, first and second order do some blue book problems. You make up the elementary steps and you need to make sure it's physically reasonable and the end result is the overall reaction.
My question would be ICE problems. I'm just not sure when I use them and how I get from the ICE chart to the answer. I know that's a vague question but any help would be appreciated.
"When" you use them: You are trying to determine equilibrium amounts from initial amounts and it is an equilibrium reaction.
DeleteHow to use the table: Initial concentrations given in the problem (usually given) go in the first line (the initial line) and then the change line is given by the coefficients of the balanced equation. The equilibrium line is given by the initial line and the change line.
From what I can understand, ICE problems depend on what's initially given. You can be given the concentrations of reactants or products and asked to determine the values for the missing information. For example:
ReplyDeleteNaOH(aq) + HCl(aq) <-> NaCl(aq) + H2O(aq)
if you are given initial values for the reactants, the initial values for the products will be 0 unless instructed otherwise. The changes for the reactants will be +x, where the changes for the products will be -x in this example. The number of x depends of the number of moles from the chemical formula. For example, 2H2 + O2 <-> 2H2O, the changes for H2 and O2 would be +2x and +x, respectfully, and for H2O would be -2x. The equilibrium line is where you combine the initial values and changes and from there you use the Kc value to determine the value of x through the equation for Kc. If you are given initial values for the products then you flip the given equation [so you'd use NaCl(aq) + H2O(aq) <-> NaOH(aq) + HCl(aq)] but the values for the changes are still -x. This will also flip the values used in the Kc equation. That's really the only way I can describe it without drawing anything out.
Something I might struggle with is remembering the the temperature effects on exothermic and endothermic reactions. Keyword "remembering" not that it's a hard concept but I'll make it easy on the next person.
I was wrong about flipping the values for the Kc equation when initial values of products are given, sorry.
ReplyDeleteA good way to think about it is exothermic loses heat and decreasing heat it will increase the K. Endothermic takes in heat so and increasing the heat will increase the k.
ReplyDeleteI have been having trouble remembering the the difference between rate constant and the equilibrium constant. Does anyone a good way of remembering the difference between the two.
Thanks for your responses!
ReplyDelete