Hello everyone, I have been working on several exercises for the past several days, and there are some I just can't seem to do. I would appreciate some help! =) 1) We have the following reaction: C2H5Br (alc) + OH(-) (alc) --> C2H5OH (l) + Br(-) The (-) indicates it's an ion. The reaction is 1st order in the reactants. We have a [ ] for each of the reactants, and the rate of disappearance of C2H5Br. -We need to find the value of the rate constant. Do we use the formula r=k[A] and get k? Why did they give us the rate of disappearance though? - If we were to double the ethyl alcohol, what would happen to the disappearance rate? I have to say, I have no idea how to do that... Does it just mean that since the concentration is less than, the rate of disappearance is less than.. as well? 2) Here, I am sure I missed something important, but I just can find clues anywhere, not in the book, not in the lecture, nowhere... We have a reaction (combustion of ethylene). If we decrease the concentration of 1 of the 2 reactant at a rate = (some number), what are the rates of change in the concentration of the products? I don't understand how I can do that if we don't know the r of the other reactant. 3) One I tried OVER and OVER and it's not giving a reasonable answer. If you want to help with just one question, please start with this one =) We have a 1st order rate reaction, and the rate constant for the decomposition of reactant A. We start with x amount of A in moles, in a volume of 2.0L (I don't know what to do with that 2.0 L. Do I just ignore it? Do I divide the x amount of A by 2 to get an amout per 1L?). We need to know the amount of A in moles after 2.5 minutes. I know that the formula is: ln [A]t = -kt + ln [A]o We have [A] at t=0. We have t. We have k. It should all be very simple. But I keep getting answer that are way to high. So, I probably should do something with that 2L. I tried keeping it. I tried dividing by 2. I tried multiplying the t to get seconds, and simplify. Any ideas? For more clarity, here's the whole thing: N2O5 --> 2NOw + O2. K= 6.82 x 10^-3 s^-1. [N2O5]= 0.0250 mol/ 2L. How many moles remain after 2.5 minutes? 4) Finally, (we had lots of exercises. I could do many, but these, I couldn't, for some reason): We have several temperatures and their corresponding k (in M^-1s^-1). We need to find the activation energy and A. My question is, how can I do this if I don't have R (for the Arrhenius equation)?! I plug in everything I can, but this unknown R prevents me from getting an answer. Or do we just need an answer in the form of R(answer)? I don't think so though... THANKS A LOT if you can help me. Or even if you try =) Joanna.