Search found 36 matches

by Melissa Bu 1B
Sun Mar 10, 2019 5:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining Step
Replies: 2
Views: 62

Re: Rate Determining Step

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.
by Melissa Bu 1B
Sun Mar 10, 2019 5:18 pm
Forum: Second Order Reactions
Topic: pseudo-first-order reaction
Replies: 4
Views: 98

Re: pseudo-first-order reaction

pseudo first order reactions are second order reactions which under some conditions (as described above) behave like first order reactions
by Melissa Bu 1B
Sun Mar 10, 2019 5:16 pm
Forum: Second Order Reactions
Topic: pseudo first order rxns
Replies: 3
Views: 59

Re: pseudo first order rxns

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...
by Melissa Bu 1B
Sun Mar 10, 2019 5:13 pm
Forum: First Order Reactions
Topic: Graphs
Replies: 2
Views: 52

Re: Graphs

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.
by Melissa Bu 1B
Sun Mar 10, 2019 5:11 pm
Forum: Zero Order Reactions
Topic: how do we tell if a reaction is zero order?
Replies: 5
Views: 101

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

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...
by Melissa Bu 1B
Sun Mar 10, 2019 5:09 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: What does unique rate of reaction mean?
Replies: 6
Views: 134

Re: What does unique rate of reaction mean?

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.
by Melissa Bu 1B
Fri Mar 08, 2019 12:17 am
Forum: Zero Order Reactions
Topic: initial concentration
Replies: 6
Views: 107

Re: initial concentration

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).
by Melissa Bu 1B
Fri Mar 08, 2019 12:16 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 4
Views: 87

Re: Units of k

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.
by Melissa Bu 1B
Fri Mar 08, 2019 12:14 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics vs thermodynamics
Replies: 3
Views: 78

Re: kinetics vs thermodynamics

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.
by Melissa Bu 1B
Sun Mar 03, 2019 2:13 pm
Forum: General Rate Laws
Topic: unique rate
Replies: 2
Views: 31

Re: unique rate

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.
by Melissa Bu 1B
Sun Mar 03, 2019 2:08 pm
Forum: Balancing Redox Reactions
Topic: Adding H+ and H2O
Replies: 13
Views: 211

Re: Adding H+ and H2O

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.
by Melissa Bu 1B
Sun Mar 03, 2019 2:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams and solids
Replies: 9
Views: 154

Re: Cell diagrams and solids

If there is a solid or liquid (like Hg (mercury)), an inert solid like Pt(s) is not needed
by Melissa Bu 1B
Sat Feb 23, 2019 3:31 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.9 6th Edition
Replies: 2
Views: 54

Re: 14.9 6th Edition

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...
by Melissa Bu 1B
Sat Feb 23, 2019 3:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 3
Views: 47

Re: Salt Bridge

In addition, the salt bridge neutralizes the two solutions as they become charged due to electron transfer between the metal electrodes.
by Melissa Bu 1B
Sat Feb 23, 2019 3:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Help
Replies: 7
Views: 127

Re: Test 2 Help

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.
by Melissa Bu 1B
Mon Feb 18, 2019 10:19 am
Forum: Phase Changes & Related Calculations
Topic: Negative and Positive values of delta H and w
Replies: 6
Views: 238

Re: Negative and Positive values of delta H and w

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)
by Melissa Bu 1B
Mon Feb 18, 2019 10:16 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Battery
Replies: 5
Views: 97

Re: Battery

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.
by Melissa Bu 1B
Mon Feb 18, 2019 10:13 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Endothermic and Exothermic Graphs
Replies: 3
Views: 67

Re: Endothermic and Exothermic Graphs

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.
by Melissa Bu 1B
Mon Feb 11, 2019 9:48 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: General entropy question
Replies: 9
Views: 123

Re: General entropy question

Adding heat, increasing temperature, making the substance a gas, increasing the volume of the substance all increase entropy
by Melissa Bu 1B
Mon Feb 11, 2019 9:42 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: why is H negative when calculating S?
Replies: 4
Views: 81

Re: why is H negative when calculating S?

When you go from a liquid to a solid, delta S is negative because the molecules are more ordered (less disordered).
by Melissa Bu 1B
Mon Feb 11, 2019 9:22 am
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 7241

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

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.
by Melissa Bu 1B
Tue Feb 05, 2019 10:54 pm
Forum: Calculating Work of Expansion
Topic: +/- work values
Replies: 5
Views: 97

Re: +/- work values

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."
by Melissa Bu 1B
Tue Feb 05, 2019 10:50 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Bomb Calorimeter
Replies: 4
Views: 77

Re: Bomb Calorimeter

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...
by Melissa Bu 1B
Tue Feb 05, 2019 10:48 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Reversible vs Irreversible
Replies: 2
Views: 77

Re: Reversible vs Irreversible

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...
by Melissa Bu 1B
Sun Feb 03, 2019 10:12 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What does "reversible isothermal" mean?
Replies: 1
Views: 42

What does "reversible isothermal" mean?

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?
by Melissa Bu 1B
Tue Jan 29, 2019 11:35 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U vs Delta H
Replies: 6
Views: 89

Re: Delta U vs Delta H

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...
by Melissa Bu 1B
Tue Jan 29, 2019 11:29 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Standard enthalpy of formation vs. enthalpy of formation
Replies: 3
Views: 47

Standard enthalpy of formation vs. enthalpy of formation

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...
by Melissa Bu 1B
Tue Jan 29, 2019 11:21 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Lecture
Replies: 5
Views: 89

Re: Lecture

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).
by Melissa Bu 1B
Mon Jan 21, 2019 10:43 am
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 7241

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

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.
by Melissa Bu 1B
Wed Jan 16, 2019 2:45 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic vs. Endothermic Reaction
Replies: 9
Views: 150

Re: Exothermic vs. Endothermic Reaction

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...
by Melissa Bu 1B
Wed Jan 16, 2019 2:41 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.69 (6th Edition)
Replies: 3
Views: 45

Re: 11.69 (6th Edition)

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...
by Melissa Bu 1B
Wed Jan 16, 2019 2:34 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Number 115 Chapter 11 HW
Replies: 2
Views: 40

Re: Number 115 Chapter 11 HW

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...
by Melissa Bu 1B
Wed Jan 09, 2019 7:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework problem 11.89 6th edition
Replies: 1
Views: 54

Homework problem 11.89 6th edition

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 ...
by Melissa Bu 1B
Tue Jan 08, 2019 10:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constants Kp notation
Replies: 2
Views: 43

Re: Equilibrium constants Kp notation

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).
by Melissa Bu 1B
Tue Jan 08, 2019 9:59 pm
Forum: Ideal Gases
Topic: Activity
Replies: 3
Views: 84

Re: Activity

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).
by Melissa Bu 1B
Tue Jan 08, 2019 9:53 pm
Forum: Ideal Gases
Topic: Conversion
Replies: 1
Views: 35

Re: Conversion

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...

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