November 3rd 2009: Tomorrow we will finish chapter 7 concerning mixtures. I like the phase diagram concerning liquid-liquid mixtures. Then we will start a key chapter concerning Chemical Equilibrium.
November 4th 2009: (From Motel 6, El Paso). We did indeed finish chapter 7 (5 in the 8th ed.). We drew some temperature composition diagrams and illustrated distillation. I remember that we discussed how distillation is not a successful separations method when the mixture forms an "azeotrope". Lastly, we drew some weird and wild liquid-liquid temperature composition diagrams showing how we can have one phase when either component is in excess, but two phases when we have comparable amounts. Next we moved on to discuss the very important idea of chemical equilibrium We understand this in thermo as the point at which the reaction Gibbs energy is zero. On friday we will further discuss the "extent of reaction" (xi, or "squiggle"), the reaction quotient (Q) and the equilibrium constant, K. See you then!
November 6th 2009: So if Delta_r G is negative a reaction proceeds left to right. If positive the reaction goes right to left. If zero then the reaction is at equilibrium. The important equation is: Delta_r G = Delta_r G(standard) + RT ln (product of activities raised to the power of their stoichiometric numbers). Delta_r G(standard) comes from the sum of the Delta_f G(standards). We are going to learn (i) how to determine which direction a reaction happens in, (ii) Delta_r G at the start of a reaction, and (iii) how much of the products and reactants we have left at the end of the reaction.
November 9th 2009: To start the week we worked a long example concerning a simple reaction. We wanted to know which way the reaction proceeded, the equilibrium constant, and the final amounts of the components at equilibrium. I tried to stress that you have to be cautious in evaluating how much of each component you have left at equilibrium because it depends upon which way the reaction is going. We talked through an example on water dissociation. We have our 3rd exam this wednesday at 1pm. Good luck studying. I will be around tomorrow (tuesday) to try and answer any questions.
November 11th 2009: So today was exam day. Exam 3. It was admittedly a tough test. I will have your exams graded by monday.
November 13th 2009: Yikes Friday the 13th! Today we finished the thermodynamics portion of PChem 1 - Chapters 1 through 9 (7th edition) or 1 through 7 (8th edition). In todays class we talked about the effect of pressure and temperature on equilibrium. We found that a reactive system will respond to a stimulus in such a way as to remove the effect of the stimulus. So if a reaction makes 2 gas molecules from one, an increase in pressure will favor the reactants. If a reaction is endothermic an increase in temperature favors the reactants. Looking forward to seeing you on Monday where we will begin kinetics! As always come see me if this isn't clear. Have a great weekend.
November 16th 2009: Today we began a new section on chemical kinetics. We discussed how this area of science is concerned with the rate of a chemical reaction. The rate can be slow or fast. Today we just showed that the rate of a reaction can be expressed as (i) a derivative (change in concentration of a reaction component wrt time) and also, (ii) an experimentally determined dependence on the concentrations of reaction components raised to some power multiplied by a rate constant. The later comes from experiment. On Wednesday we'll discuss how we get the form of the rate law from an experiment.
November 18th 2009: So, first of all, don't forget free pizza in the chem lounge tomorrow (thursday) at noon. Second, great news! The chemistry math class has been approved and will be going ahead this spring - Chem 4980 - tell your friends! Okay, back to todays class. Just how do you figure out the form of the rate law for a chemical reaction? Well, there are two things we can do, first the isolation method. This method reduces the rate law into a much simpler form. Second, the method of initial rates. This method can tell us the order of the reaction wrt that component. We then began talking about integrated rate laws because we want to be able to know how much product/reactant we have left after a given amount of reaction time. More on this on friday. In the mean time Freeee Pizzzaaaa!
November 21st 2009: In class on friday we looked at integrated rate laws. We looked at simple first order rate laws, and then two types of second order rate laws. We saw how the three different cases can be discerned by plotting - whether we get a straight line or not can tell us what order our reaction is. On monday we will begin to consider rates near equilibrium and the effect of temp on rate.
November 23rd 2009: So the equilibrium constant for a simple A to B reaction is equal to the rate constant for the forward reaction divided by the rate constant for the backward reaction. Who knew! Also we followed Arrhenius in noticing that a plot of ln k vs 1/T is often (usually) linear! If we fit a straight line to the ln k vs 1/t plot we find the slope and intercept have physical meaning! The slope tells us the activation energy. The intercept tells how often collisions are occurring. We finished by setting the scene for discussing reaction mechanisms. Okay, back to monday night football.
November 25th 2009: We focused on concepts! Kinetics can tell us whether an intermediate exists in a reaction. Reaction rates depend upon rate determining steps. Approximations are useful, i.e. the steady state approximation. We will do some math on monday. Happy thanksgiving!