CHEMISTRY COMMUNITY

Melissa Bu 1B

It does not matter which elementary step (first, second, third, etc) is the slow step. It only matters that the slow step in the reaction mechanism determines the rate of the reaction.

Melissa Bu 1B

pseudo first order reactions are second order reactions which under some conditions (as described above) behave like first order reactions

Melissa Bu 1B

At the kinetics review session today, the facilitator said that we likely will not be tested mathematically on pseudo-first order reactions. We just need to know conceptually that pseudo-first order reactions are second order reactions which under some particular conditions (as described above), loo...

Melissa Bu 1B

I think you can tell the reaction order of a reaction by looking at the graphs and their axes (as mentioned above). However, I am not sure if you can mathematically compute the reaction order from a graph.

Melissa Bu 1B

As my peers have indicated previously, a zero order reaction's rate does not depend on the initial concentration of the reactant. No matter what initial concentration it has, the rate of the reaction will proceed at one certain speed. Also, first and second order reactions have concentration vs. tim...

Melissa Bu 1B

The unique rate of each reactant and product are the same in a reaction because the changes are with regards to each species' coefficient. The average and instantaneous rates of each reactant and product in a reaction may differ.

Melissa Bu 1B

The characteristic of zero order reactions is that they occur at a rate that is independent of the initial concentration. No matter how much of a reactant you have initially, the reaction will proceed at the same rate (that of the rate constant, k).

Melissa Bu 1B

To find the units of k depending on the reaction order, simply plug in M/s for Rate and M for the concentrations present. Then solve for the units of k using algebra.

Melissa Bu 1B

thermodynamics tells us whether a reaction will occur at all (if it has the favorable conditions of being exothermic and spontaneous). kinetics tell us how fast, or the rate of, a given reaction under the condition that it does occur/is thermodynamically favorable.

Melissa Bu 1B

The unique rate is the same of products and reactants in that unique reaction.

given aA-->bB+cC,
unique rate=-1/a * [A]=1/b * [B] = 1/c * [C]

Instantaneous rates can be different among reactants and products of a reaction because their coefficients are not considered.

Melissa Bu 1B

To balance H+ in a basic solution, add one molecule of H20 per every H+ you need. Then, add that same number of OH- on the opposite side.

Melissa Bu 1B

If there is a solid or liquid (like Hg (mercury)), an inert solid like Pt(s) is not needed

Melissa Bu 1B

I am also not sure about how I is being oxidized since its oxidation number is -1 on both sides of the equation. As for the number of moles of electrons transferred, I believe we have to refer to the electrochemical series. The reduction equation for Ce4+ + e- --> Ce3+ in the table in Appendix 2B in...

Melissa Bu 1B

In addition, the salt bridge neutralizes the two solutions as they become charged due to electron transfer between the metal electrodes.

Melissa Bu 1B

I asked him about that equation after class on Friday and he says it is fair game because we can derive it ourselves from deltaG=-RTlnK and deltaG=-nFE but setting them equal to each other and dividing both sides by -RT.

Melissa Bu 1B

w>0 means work is being done on the system
w<0 means work is being done by the system
H>0 means the system requires heat (heat flows in)
H<0 means the system release heat (heat flows out)

Melissa Bu 1B

I would also say a battery is a closed system because although it cannot transfer matter into its surroundings, it can certainly transfer electrical energy.

Melissa Bu 1B

We often discuss endothermic and exothermic reactions as absorbing heat and releasing heat, respectively. Heat is a form of energy, which is why energy is on the y axis.

Melissa Bu 1B

Adding heat, increasing temperature, making the substance a gas, increasing the volume of the substance all increase entropy

Melissa Bu 1B

When you go from a liquid to a solid, delta S is negative because the molecules are more ordered (less disordered).

Melissa Bu 1B

I got +312kJ initially too, but I think the question is more complicated in that you have to write out the combustion equations of the three equations given and then use Hess' Law. When you do that, you get -312kJ.

Melissa Bu 1B

An abstract way to think about work's + vs - values is that when work is being done ON the system, w is positive because there is "work added into the system." Conversely, when work is done BY the system, w is negative because "the system is losing work."

Melissa Bu 1B

Like above comments have mentioned, there is no change in volume in a bomb calorimeter. With this in mind while calculating change in internal energy (delta U) where delta U=q+w and w=-PdeltaV, w would be equal to 0 since delta V is 0. Therefore, the internal energy change (delta U) of a bomb calori...

Melissa Bu 1B

Isothermal, reversible expansions generate the maximum work. Since work is the area under a curve (of P on the x-axis and V on the y-axis), imagine the area shaded under the curve of the reversible expansion to be almost touching the curve itself since the changes in volume are so small. Alternative...

Melissa Bu 1B

The textbook references "reversible isothermal" expansions and concludes that these expansions have an internal energy change of 0. Does this correlate to Dr. Lavelle's "isolated system" (reaction in a bomb calorimeter) example from lecture 11?

Melissa Bu 1B

It is also noteworthy that the equation deltaH=deltaU+(P)deltaV is only applicable in the case that the heat is supplied to the system at a constant pressure. deltaU is also equal to q + w, where q describes molecules moving in random direction and w describes molecules moving in a definite directio...

Melissa Bu 1B

Is the difference between "standard enthalpy of formation" and "enthalpy of formation" just that the reactants and products of the "standard enthalpy of formation" reaction are in their standard states and those in a reaction asking for the "enthalpy of formation&q...

Melissa Bu 1B

Moreover, the heating curve showed that water vapor burns more than liquid water even though they are at the same temperature (100˚C, shown on Y axis), because water vapor has more heat than liquid water (shown by the fact that it is further right on the X axis, which represents heat).

Melissa Bu 1B

Did anyone happen to get around 0.077g for #2 on the acid-base review worksheet? The key says 0.10g, so I am unsure whether Karen rounded or I did the question incorrectly.

Melissa Bu 1B

It helps to see an energy graph to think about why exothermic has a negative change in H and endothermic has a positive change in H. In exothermic reactions, heat is leaving the system, so the graph will end up at a lower delta H value in the products compared to the reactants. Therefore, the change...

Melissa Bu 1B

The equilibrium constant K is a constant that describes the ratio of concentrations of products/concentrations of reactants at equilibrium (when the rate of the forward reaction is equal to the rate of the reverse reaction). Therefore, it is only "relevant" when the reaction is at equilibr...

Melissa Bu 1B

I believe the "quick way" Dr. Lavelle described in class to determine which way the reaction shifts when the pressure increases only applies for moles of gas, not gas and aqueous solutions. The quick way is to see which side has fewer moles of gas and the reaction will proceed in that dire...

Melissa Bu 1B

Could anyone please explain why the total pressure is 100 for 11.89 in the 6th edition? 11.89 The following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound A into compounds B and C. All three compounds are gases. Use this plot to do the ...

Melissa Bu 1B

For Kp, the solution manual shows the values of partial pressures in parentheses. Just putting CO2 in brackets like [CO2] is the concentration of CO2, which is correct for a Kc expression but incorrect for Kp. Instead, for pressures, I believe we should use parentheses like so: (P subscript CO2).

Melissa Bu 1B

Instead of using activity, we use molarities (concentration) in our calculations of the equilibrium constant value which is a close approximation to activities (more accurate but harder to measure).

Melissa Bu 1B

Dr. Lavelle used PV=nRT to convert between pressure and concentration. Concentration is in molarity, which is defined by moles over L. In the Ideal Gas Law, moles is expressed by "n" and L is expressed by "V," the volume. If we divide both sides of the Ideal Gas Law by V, we will...

CHEMISTRY COMMUNITY

Search found 36 matches

Re: Rate Determining Step

Re: pseudo-first-order reaction

Re: pseudo first order rxns

Re: Graphs

Re: how do we tell if a reaction is zero order?

Re: What does unique rate of reaction mean?

Re: initial concentration

Re: Units of k

Re: kinetics vs thermodynamics

Re: unique rate

Re: Adding H+ and H2O

Re: Cell diagrams and solids

Re: 14.9 6th Edition

Re: Salt Bridge

Re: Test 2 Help

Re: Negative and Positive values of delta H and w

Re: Battery

Re: Endothermic and Exothermic Graphs

Re: General entropy question

Re: why is H negative when calculating S?

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Re: +/- work values

Re: Bomb Calorimeter

Re: Reversible vs Irreversible

What does "reversible isothermal" mean?

Re: Delta U vs Delta H

Standard enthalpy of formation vs. enthalpy of formation

Re: Lecture

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Re: Exothermic vs. Endothermic Reaction

Re: 11.69 (6th Edition)

Re: Number 115 Chapter 11 HW

Homework problem 11.89 6th edition

Re: Equilibrium constants Kp notation

Re: Activity

Re: Conversion