## Search found 56 matches

Fri Mar 13, 2020 7:40 am
Forum: Administrative Questions and Class Announcements
Topic: Final
Replies: 12
Views: 312

### Re: Final

I will not have access to a printer in that 3 hour timeslot; if a TA or someone could clarify how we are meant to turn in the final that would be very helpful.
Thu Mar 12, 2020 11:55 am
Forum: General Rate Laws
Topic: When do we acknowledge temperature in identifying rate?
Replies: 3
Views: 56

### Re: When do we acknowledge temperature in identifying rate?

Thu Mar 12, 2020 11:55 am
Forum: First Order Reactions
Topic: Units for t
Replies: 13
Views: 190

### Re: Units for t

Just to ensure I didn't mix up anything I usually convert everything to seconds before trying to solve the problem - if it asks to be expressed in minutes or hours you can convert back at the end.
Thu Mar 12, 2020 11:52 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta U= delta H
Replies: 6
Views: 164

### Re: delta U= delta H

viewtopic.php?t=25381
Were also pretty helpful for me sorting it out in my head, hope they help!
Thu Mar 12, 2020 11:51 am
Forum: General Rate Laws
Topic: When do we acknowledge temperature in identifying rate?
Replies: 3
Views: 56

### When do we acknowledge temperature in identifying rate?

I'm confused in what situation we would have to incorporate temperature in our solutions to kinetics-based questions. It seems that for many questions, rate constants are not affected by a provided temperature, but I know that reactions occur faster when temperature is increased. In what type of que...
Thu Mar 12, 2020 11:47 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Balanced Chemical Equations
Replies: 4
Views: 169

### Re: Balanced Chemical Equations

An example for the above reply would be in the case of CH3OH + (3/2)O2 = CO2 + (2)H2O...
You'd multiply both sides by 2 to get (2)CH3OH + (3)O2 = (2)CO2 + (4)H2O
Thu Mar 12, 2020 11:44 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy of ideal gas
Replies: 6
Views: 191

### Re: Internal energy of ideal gas

They DO have internal energy, but there is no change in internal energy. Basically, because ideal gas are extremely non-reactive particles (already fully stable), they don't "see" each other at all. The average kinetic energy is nothing else than the temperature of the ideal gas, and if th...
Thu Mar 12, 2020 11:40 am
Forum: Administrative Questions and Class Announcements
Topic: Lecture 4 Week 10 notes and Kinetics review
Replies: 2
Views: 246

### Re: Lecture 4 Week 10 notes and Kinetics review

Thank you so much! Very helpful.
Thu Mar 12, 2020 11:36 am
Forum: General Rate Laws
Topic: Units of time
Replies: 5
Views: 69

### Units of time

Is rate always expressed with seconds as the measurement of time? Or could a rate law be expressed in M/hr?
Thu Mar 12, 2020 11:34 am
Forum: Zero Order Reactions
Topic: All reactants zero order?
Replies: 7
Views: 163

### All reactants zero order?

Could there ever be a reaction in which all reactants are zero order and thus the reaction itself is zeroth order? What would be an example of this?
Thu Mar 12, 2020 11:32 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7A.11) 700K?
Replies: 6
Views: 114

### 7A.11) 700K?

For 7A. 11, should we ignore the mention of the reaction occuring at 700 K? If not, I'm unsure of how to incorporate this into the rate law.
Thu Mar 12, 2020 11:29 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: U vs H
Replies: 15
Views: 364

### Re: U vs H

A note on delta U being expressed the change in internal energy; (U=w+q); w is often expressed interchangeably as work done on the system and work done BY the system. For the former, it is w+q; for the latter, it is actually -w+q because the work done by the system is still positive but it results i...
Thu Mar 12, 2020 11:23 am
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: Environment and Fossil Fuels [ENDORSED]
Replies: 2
Views: 283

### Re: Environment and Fossil Fuels[ENDORSED]

Although electric vehicles are not entirely zero emission, they ultimately convert over much more of the energy from fossil fuels power at the wheels. Conventional gasoline vehicles only convert a small fraction of the energy stored in gasoline to power at the wheels
Thu Mar 12, 2020 11:20 am
Forum: Ideal Gases
Topic: Liter to meter cubed?
Replies: 4
Views: 151

### Re: Liter to meter cubed?

My AP Chem teacher was an Ozzy and always used: Kangaroos Hop Down Mountains Drinking Choccy Milk. Not that one's better than the other, but I've always remembered it through that acronym :)
Thu Mar 12, 2020 11:18 am
Forum: Ideal Gases
Topic: Acids and Basis: Salts
Replies: 9
Views: 167

### Re: Acids and Basis: Salts

It's a good idea to memorize which bases and acids are strong so you can know exactly when to apply the above methods mentioned.
Thu Mar 12, 2020 11:17 am
Forum: Ideal Gases
Topic: Partial Pressure
Replies: 13
Views: 215

### Re: Partial Pressure

This is a feature of Le Chatelier's Principle; I think it should be in Week 3 notes if that helps!
Thu Mar 12, 2020 11:12 am
Forum: General Rate Laws
Topic: Units
Replies: 4
Views: 91

### Re: Units

Zeroth order: M * s^-1
First order: s^-1
Second Order: M^-1 * s^-1
etc.
Thu Mar 12, 2020 11:11 am
Forum: General Rate Laws
Topic: 7A.3A Reaction Concentration
Replies: 3
Views: 65

### Re: 7A.3A Reaction Concentration

It helps me to isolate the reactant's effects on rate in an algebraic format.
2A = 4
2A*2B=8
Where A and B are the reactant's orders.
Therefore A must equal 2 and B must equal 1.
Thu Mar 12, 2020 11:06 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Kelvin or Celsius?
Replies: 59
Views: 1323

### Re: Kelvin or Celsius?

Kelvin = Celsius + 273.15; the two are on the same scale so converting between the two isn't too tricky.
Thu Mar 12, 2020 11:05 am
Forum: Zero Order Reactions
Topic: Zeroeth, First, Second meaning
Replies: 6
Views: 174

### Re: Zeroeth, First, Second meaning

Also, note that just because a reactant is first order, doesn't necessarily mean the reaction itself is as well. If multiple reactants are first order, the reaction is the sum of those reactants (So if N and O were both first order in forming NO, the reaction is second order).
Thu Mar 12, 2020 11:03 am
Forum: Zero Order Reactions
Topic: Graphs
Replies: 13
Views: 606

### Re: Graphs

Also it might be a good idea to memorize the y-axis for various orders of reactions (zeroth [A], first ln[A], second 1/[A])
Thu Mar 12, 2020 11:02 am
Forum: Zero Order Reactions
Topic: Identifying Zero vs. First vs. Second Order Reactions
Replies: 7
Views: 114

### Re: Identifying Zero vs. First vs. Second Order Reactions

Also, if you are given various rates provided reactant concentrations, and rate does not change as a reactant concentration is increased or decreased, you know it is zeroth order. If it changes proportionately, it is first. If it changes exponentially, it is second or third or above.
Thu Mar 12, 2020 11:00 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Units
Replies: 8
Views: 216

### Re: Units

The above post also applies for third order reactions; M would be squared in the denominator.
Thu Mar 12, 2020 10:59 am
Forum: Zero Order Reactions
Topic: Example Help
Replies: 6
Views: 171

### Re: Example Help

You can identify a reactant as zero-order if changing its concentration does not affect the rate in any way.
Tue Mar 10, 2020 10:06 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: How to calculate for n
Replies: 7
Views: 164

### Re: How to calculate for n

It should be noted that some balancing is necessary to identify n, which is the balanced amount of electrons between the two redox reactions. For instance, with an oxidation that loses 2 electrons and a reduction that gains 3, n would be 6. I would
Tue Mar 10, 2020 10:02 pm
Forum: Administrative Questions and Class Announcements
Topic: Email Announcement
Replies: 8
Views: 251

### Re: Email Announcement

I heard review sessions might be Bruincasted in some manner but nothing is set in stone until Dr. Lavelle emails us.
Tue Mar 03, 2020 11:42 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Units for G°
Replies: 6
Views: 78

### Units for G°

Should standard reaction Gibbs free energy be expressed in joules (or kJ) per mole? Or simply in joules alone?

The textbook says the latter, whereas the solutions manual says the former.

Thanks
Wed Feb 12, 2020 10:58 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding change in internal energy using PV=nRT equation
Replies: 3
Views: 1775

### Re: Finding change in internal energy using PV=nRT equation

Since the reaction doesn't specify, we can assume T=298K (room temperature). However, this is a typo on the textbook's part; they should have specified T.
Wed Feb 12, 2020 10:40 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45 Preparation of Carbon Disulfide
Replies: 2
Views: 1989

### Re: 8.45 Preparation of Carbon Disulfide

a) (1.25mol S8) * (358.8 kJ/1mol S8) = 448.5 kJ
b) (197g C) * (1mol C/12.01g C) * (358kJ/4 mol C) = 1471.35 kJ
c) (415 kJ/358.8kJ) = (x mol CS2/4mol CS2); x = 4.63mol CS2
Tue Feb 11, 2020 10:23 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating [CO2] given pH and [HCO3-]
Replies: 1
Views: 40

### Calculating [CO2] given pH and [HCO3-]

I've been looking at past study guides and one question kind of threw me off, as 10^-6.1 is used for both K and [H3O+] H3O+(aq) + HCO3− (aq) ⇌ 2H2O(l) + CO2(aq); K = 7.9 × 10-7 This reaction assumes that all H2CO3 produced decomposes completely to CO2 and H2O. Suppose that 1.0 L of blood is brought ...
Tue Feb 11, 2020 10:01 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acid and [H3O] Midterm Q
Replies: 3
Views: 70

### Acid and [H3O] Midterm Q

I found this question from a study guide from a few years ago and was hoping someone could explain the answer (in bold).

For a 0.10 M solution of a weak acid, HA, with pKa = 10, which of the following is true?

[HA] ≅ 0
[HA] = Ka
[HA] = [A−]
[HA] ≠ [H3O+]
[HA] = [H3O+
Fri Feb 07, 2020 8:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equation
Replies: 3
Views: 78

### Re: Equation

What are we meant to use if it is not reversible expansion?
Fri Feb 07, 2020 8:50 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Replies: 3
Views: 58

Also adding onto this question if that’s okay, do adiabatic and isothermal mean the same thing?
Fri Feb 07, 2020 8:49 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Expansion Explained
Replies: 7
Views: 120

### Irreversible Expansion Explained

Can someone clarify what exactly an irreversible expansion would look like? As in explain it with an analogy; something besides the piston one.
Fri Feb 07, 2020 8:39 pm
Forum: Phase Changes & Related Calculations
Topic: -w vs w
Replies: 15
Views: 180

### Re: -w vs w

This can become sort of confusing as U is said to equal both Q+W and Q-W; just try to keep in mind that internal energy is lost if the system DOES work; in the first equation this would mean W is negative and in the second it would be positive. Both mean the same thing.
Fri Feb 07, 2020 8:33 pm
Forum: Phase Changes & Related Calculations
Topic: Negative Work
Replies: 18
Views: 387

### Re: Negative Work

The equations U=Q-W and U=Q+W are used interchangeably; instead of memorizing one or the other it helps to think about whether work is being done BY the system (in many contexts, expansion of a gas) or TO the system (compression).
Thu Jan 30, 2020 10:12 am
Forum: Phase Changes & Related Calculations
Topic: Units
Replies: 16
Views: 176

### Re: Units

°C = K + 273.15; there is no multiplication involved and thus the scale is proportional.
Thu Jan 30, 2020 10:11 am
Forum: Calculating Work of Expansion
Topic: Integral
Replies: 4
Views: 48

### Re: Integral

I also had confusion with this part of the lecture as I'm currently in Math 3B and we haven't covered integrals yet; if someone could clarify what exactly v1{v2 means that'd be great.
Thu Jan 30, 2020 10:09 am
Forum: Phase Changes & Related Calculations
Topic: 4A. 1 Identifying open and closed system
Replies: 11
Views: 278

### Re: 4A. 1 Identifying open and closed system

d is an open system because matter is allowed to exit the engine through the exhaust in the form of CO2
Thu Jan 30, 2020 10:08 am
Forum: Phase Changes & Related Calculations
Topic: 4B.1
Replies: 6
Views: 88

### Re: 4B.1

Think about the energy of the gas; because a force is being exerted on it (W), that results in an increased pressure and energy (U) in that system - it might heat up as a result.
Wed Jan 29, 2020 9:59 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Calorimeters as Isolated Systems
Replies: 2
Views: 53

### Calorimeters as Isolated Systems

I may be misunderstanding definitions, but how can a bomb calorimeter be an isolated system if energy is allowed to transfer to the water? Doesn’t an isolated system mean matter and energy exchange is not allowed?
Fri Jan 24, 2020 12:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: equilibrium
Replies: 3
Views: 42

### Re: equilibrium

Yes. That equilibrium could technically be 0, meaning no product forms, or an infinitely large value, meaning all reactants turn into product, or some intermediate value of the two. In any case, some equilibrium will generally be reached in my knowledge.
Fri Jan 24, 2020 12:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: salt solutions
Replies: 4
Views: 73

### Re: salt solutions

Buffers are generally made of certain pairs of solutes, either a weak acid plus a salt derived from that weak acid or a weak base plus a salt of that weak base. For example, a buffer can be composed of dissolved acetic acid (HC 2H 3O 2, a weak acid) and sodium acetate (NaC 2H 3O 2, a salt derived fr...
Fri Jan 24, 2020 12:29 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Using Kc Vs Kp
Replies: 22
Views: 245

### Re: Using Kc Vs Kp

There is no unit for Kc or Kp, it is simply a value used to represent the ratio of product and reactant concentration at equilibrium
Fri Jan 24, 2020 12:27 pm
Forum: Phase Changes & Related Calculations
Topic: Steam vs liquid
Replies: 7
Views: 88

### Re: Steam vs liquid

It should be added that when steam condenses on skin it adds to the amount of energy; it’s the joules from the phase change that releases so much energy.
Fri Jan 24, 2020 12:23 pm
Forum: Ionic & Covalent Bonds
Topic: Carbon
Replies: 4
Views: 211

### Re: Carbon

Quadruple bonds technically are possible but they require the presence of four different orbitals (two S, one P, and one D); carbon cannot attain the last.
Fri Jan 24, 2020 12:20 pm
Forum: General Science Questions
Topic: Rusty on High School Chem [ENDORSED]
Replies: 212
Views: 142731

### Re: Rusty on High School Chem[ENDORSED]

Try emailing your high school teacher and seeing if they can forward you a document with all their old slides; more sources = more information, can’t hurt!
Fri Jan 24, 2020 12:15 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in Pressure
Replies: 9
Views: 99

### Re: Changes in Pressure

It is important to note that PV=nRT only stands true if the increase in pressure changes concentration; adding an inert gas such as helium to the system will increase the pressure but make the volume remain the same, thus no change in K occurs.
Tue Jan 21, 2020 3:46 pm
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 228
Views: 117610

### Re: Advice from a Medical Student[ENDORSED]

Tue Jan 21, 2020 3:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Problem 5.39
Replies: 1
Views: 33

### Re: Problem 5.39

That's what I used for this question, personally.
Tue Jan 21, 2020 3:35 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Autoprotolysis
Replies: 5
Views: 110

### Re: Autoprotolysis

It's essentially describing how H2O is also being converted into H3O+ and OH-, but at extremely small concentrations compared to the much more stable concentration of H2O.
Tue Jan 21, 2020 3:33 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: K value at a specific temp
Replies: 6
Views: 91

### Re: K value at a specific temp

Depending on the type of reaction (endothermic or exothermic), temperature affects K differently, increasing it for endothermic ones and decreasing it for exothermic ones.
Tue Jan 21, 2020 3:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentration vs. Partial Pressure
Replies: 1
Views: 42

### Concentration vs. Partial Pressure

When calculating K, should we always express it for gases in terms of partial pressure? Or should we try to convert to concentration (n/V) for them as well?
Tue Jan 21, 2020 3:30 pm
Forum: Ideal Gases
Topic: ICE Tables
Replies: 8
Views: 144

### Re: ICE Tables

+ X is generally used for products and - X for reactants, as the former is produced from reaction and the latter is used up. However, I'm sure it depends on the context of the question.
Tue Jan 21, 2020 3:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 337
Views: 139577

### Re: Saying Thank You to Dr. Lavelle

I agree, thank you so much!
Tue Jan 21, 2020 3:27 pm
Forum: Student Social/Study Group
Topic: Final Jitters
Replies: 226
Views: 35987

### Re: Final Jitters

Try to control your breathing between questions, it will slow your heartrate and calm you down!