Search found 67 matches

Mon Mar 12, 2018 5:54 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Given information
Replies: 5
Views: 290

Re: Given information

We can make out which compounds are intermediates since they are the ones that are produced in one step and then used up in another step; they are not present to begin with or left over after the reaction is over.
Mon Mar 12, 2018 5:53 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Kinetic Energy vs Potential Energy
Replies: 2
Views: 187

Re: Kinetic Energy vs Potential Energy

I don't think we have to worry about what components make up the total energy.
Mon Mar 12, 2018 5:52 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: slow step
Replies: 3
Views: 226

Re: slow step

You can only have 1 slow step and that is the step that matches the overall reaction's rate law.
Mon Mar 05, 2018 7:36 pm
Forum: General Rate Laws
Topic: Test 3 material
Replies: 6
Views: 369

Re: Test 3 material

Yes, reaction mechanisms and pseudo reactions will not be on test 3.
Mon Mar 05, 2018 7:35 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: rate constant vs rates
Replies: 2
Views: 188

Re: rate constant vs rates

The rate constant is a constant and therefore must stay the same throughout.
Mon Mar 05, 2018 7:33 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics an thermodynamics
Replies: 3
Views: 246

Re: kinetics an thermodynamics

I think you should just know that thermodynamics controls whether or not a reaction will happen (whether or not it is favorable). Kinetics controls how fast the reaction proceeds.
Mon Mar 05, 2018 7:32 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.19
Replies: 3
Views: 284

Re: 15.19

It is important to choose 2 reactions in which only the concentration of one reactant is changing. This is so that you can say for sure that the change in rate is due to the change in the concentration of that one reactant.
Mon Feb 26, 2018 3:37 pm
Forum: General Rate Laws
Topic: initial rate law
Replies: 5
Views: 240

Re: initial rate law

The more accurate method would be to analyze changes in both the reactant and product concentrations.
Mon Feb 26, 2018 3:36 pm
Forum: General Rate Laws
Topic: Reaction rates
Replies: 3
Views: 227

Re: Reaction rates

There are no products at the beginning of a reaction since none of them have been formed yet.
Mon Feb 26, 2018 3:34 pm
Forum: General Rate Laws
Topic: Units for 15.3 Part B
Replies: 4
Views: 310

Re: Units for 15.3 Part B

The solutions manual is just trying to distinguish between the different reactants and products so that the reader doesn't get confused as to why there are multiple same answers for different reactants/products.
Mon Feb 26, 2018 3:33 pm
Forum: General Rate Laws
Topic: Differential rate law
Replies: 3
Views: 216

Re: Differential rate law

I think its main use is to integrate this and use it as the integrated rate law.
Mon Feb 26, 2018 3:32 pm
Forum: General Rate Laws
Topic: Unique Rate of Reactions
Replies: 3
Views: 227

Re: Unique Rate of Reactions

All the unique rates of reactions for all the reactants and products in a reaction are the same.
Mon Feb 26, 2018 3:32 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Units of Reaction Rate
Replies: 7
Views: 452

Re: Units of Reaction Rate

Yes, you should not ignore the units of anything when using equations because the units must make sense in the final answer.
Tue Feb 20, 2018 10:09 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.27
Replies: 6
Views: 381

Re: 14.27

I think it might have to do with the fact that delta G is a state function so you can add each step's delta G to get the total.
Tue Feb 20, 2018 10:09 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15 given half reactions?
Replies: 3
Views: 223

Re: 14.15 given half reactions?

I looked in the appendix for that one since I don't think there is a straight forward way to come up with them.
Tue Feb 20, 2018 10:08 am
Forum: Balancing Redox Reactions
Topic: 14.5 part a
Replies: 2
Views: 212

Re: 14.5 part a

I think since the bromine is going from -1 to 5 (meaning it's oxidation), the oxygen would have to be reduced for this to be a redox reaction.
Tue Feb 20, 2018 10:06 am
Forum: Balancing Redox Reactions
Topic: 14.13C
Replies: 1
Views: 149

Re: 14.13C

I think it is because the change in oxidation state of H2 is associated with the hydrogen part of hydrochloric acid. And the oxidation state of Cl2 is associated with the chlorine part of hydrochloric acid. Due to this, you have to keep them separate.
Thu Feb 15, 2018 5:34 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal and deltaU=0
Replies: 3
Views: 297

Re: isothermal and deltaU=0

Once we determine that delta U = 0, we can manipulate q and w and set q=-w.
Thu Feb 15, 2018 5:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard ∆G for a system at equilibrium
Replies: 3
Views: 257

Re: Standard ∆G for a system at equilibrium

Make sure to distinguish between delta G and delta G knot since I think that is what is confusing.
Thu Feb 15, 2018 5:30 pm
Forum: Calculating Work of Expansion
Topic: Isolated System
Replies: 5
Views: 365

Re: Isolated System

This fact that delta U = 0 allows us to set q = -w and do other calculations involving heat and work.
Thu Feb 15, 2018 5:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 3
Views: 203

Re: Delta G

This is also true for enthalpy and entropy, also state functions. If the initial state and final states are the same, then the change in that quantity is zero.
Tue Feb 06, 2018 10:37 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Equipartition Theorem
Replies: 3
Views: 260

Re: Equipartition Theorem

Do we have to know this theorem for the midterm? I do not think Dr. Lavelle discussed it in very much detail in lecture.
Tue Feb 06, 2018 10:36 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: entropy
Replies: 4
Views: 248

Re: entropy

Increasing volume also results in an increase in entropy since the gas can now have more microstates.
Tue Feb 06, 2018 10:35 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: System vs Surrounding
Replies: 4
Views: 298

Re: System vs Surrounding

Is there ever a situation in which the entire beaker would be the system and for example, the Earth would be the surroundings?
Tue Feb 06, 2018 10:18 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Irreversible vs. Reversible
Replies: 2
Views: 199

Re: Irreversible vs. Reversible

Sometimes, when you are trying to calculate values for a state function, it does not matter whether you use data from reversible or irreversible reactions since all you need is final minus initial; the path does not matter.
Sat Feb 03, 2018 3:35 pm
Forum: Calculating Work of Expansion
Topic: Reversible Expansion
Replies: 3
Views: 243

Re: Reversible Expansion

In the equation S=qrev/T, why do we need to use the q for a reversible reaction?
Sat Feb 03, 2018 3:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions [ENDORSED]
Replies: 7
Views: 348

Re: State functions[ENDORSED]

Since q and w are not state functions, you cannot do calculations with just final minus initial.
Sat Feb 03, 2018 3:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: sign of q
Replies: 7
Views: 435

Re: sign of q

The system's q sign and the surrounding's q sign will always be opposites since whatever the system is losing is what the surroundings gain.
Sat Feb 03, 2018 3:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy question
Replies: 3
Views: 388

Re: Gibbs free energy question

Gibbs free energy is basically the amount of energy that is available to do useful work in the system. The equation for Gibbs free energy takes the total enthalpy of the system and subtracts whatever energy is lost through the t delta s term. The remaining energy is the amount of energy left to do u...
Mon Jan 29, 2018 10:26 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test question [ENDORSED]
Replies: 16
Views: 855

Re: Test question[ENDORSED]

I just wrote the equation, delta U = q + w.
Mon Jan 29, 2018 10:24 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Homework 9.5 [ENDORSED]
Replies: 11
Views: 628

Re: Homework 9.5[ENDORSED]

Whenever the sign of something is not immediately obvious think about whether the system or the surroundings are gaining or losing heat; losing heat is always signified by a negative sign.
Mon Jan 29, 2018 10:22 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Entropy vs. Standard Entropy
Replies: 4
Views: 286

Re: Entropy vs. Standard Entropy

I think the difference is that when you want the standard entropy, you are forming 1 mole of the product with everything in its standard states.
Mon Jan 29, 2018 10:12 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.49 [ENDORSED]
Replies: 4
Views: 313

Re: 8.49[ENDORSED]

Yes, if no other temperature is given in the problem, it is safe to assume that the reaction occurred at room temperature which is 298 K.
Mon Jan 22, 2018 11:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculations on Test 3
Replies: 3
Views: 190

Re: Calculations on Test 3

Yes and Dr. Lavelle also said we will be expected to know concepts related to work and internal energy even though we do not need to perform calculations related to them.
Mon Jan 22, 2018 11:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Different Delta H. Question 8.57
Replies: 2
Views: 206

Re: Different Delta H. Question 8.57

In problems like these (with the subscript c), you have to set up a combustion equation with the reactant and oxygen on the left and carbon dioxide and water on the right.
Mon Jan 22, 2018 11:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Reaction Sequences
Replies: 1
Views: 135

Re: Reaction Sequences

I find it easy to find the desired reactants and products and arrange them with reactants on the left and products on the right. From there, I just multiply the various equations by whatever is necessary to cancel other substances out with each other.
Mon Jan 22, 2018 11:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Problem 8.49
Replies: 3
Views: 246

Re: Problem 8.49

In most problems, if a specific temperature is not given, you should use 298K as it is considered standard.
Tue Jan 16, 2018 10:13 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Capacity
Replies: 4
Views: 305

Re: Heat Capacity

It is useful to use the specific heat capacity so that the mass becomes irrelevant. Specific heat capacity is an intensive property.
Tue Jan 16, 2018 10:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.77
Replies: 2
Views: 200

Re: 8.77

In the table of enthalpies, there is a specific number for the bonds found in a benzene ring.
Tue Jan 16, 2018 10:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess Law
Replies: 4
Views: 267

Re: Hess Law

In state properties, the path taken does not matter; only the final and initial values matter when doing calculations related to state properties.
Tue Jan 16, 2018 10:04 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.77
Replies: 2
Views: 140

Re: 8.77

The most stable form of a compound is when the electrons are as far away from each other as possible, which is what occurs in this example.
Thu Jan 11, 2018 5:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Chapter 8
Replies: 6
Views: 291

Re: Chapter 8

So far, we can also do problems 37 and 39 before number 55.
Thu Jan 11, 2018 5:20 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity: molar versus specific
Replies: 3
Views: 2093

Re: Heat Capacity: molar versus specific

Yes, whenever the mass of a substance is given in grams, use specific heat capacity. If it is given in moles, use molar heat capacity.
Thu Jan 11, 2018 5:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: #39 from Chapter 8
Replies: 3
Views: 223

Re: #39 from Chapter 8

Another mistake I ran into while solving this question was forgetting to convert the enthalpy of fusion into Joules because in the tables, it is given in kJ.
Thu Jan 11, 2018 5:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.59
Replies: 2
Views: 148

Re: 8.59

From what I understand, the only reason that nitrogen is not included is because its enthalpy is 0 if you look at the table. I don't think it has to do with the fact that it is in its gas phase.
Thu Dec 07, 2017 4:24 pm
Forum: Lewis Acids & Bases
Topic: 12.15
Replies: 3
Views: 319

Re: 12.15

Look at formal charges, you know that phosphorus likes to make 5 bonds since it has a valence number of 5, however in the case of PF6 it is making 6 bonds, resulting in a -1 charge.
Thu Dec 07, 2017 4:22 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 5% Rule for Weak Acids
Replies: 2
Views: 343

Re: 5% Rule for Weak Acids

How strict is the 5% rule? If the approximation is slightly more than 5% off, would we have to recalculate everything with more accuracy?
Tue Nov 28, 2017 8:05 pm
Forum: Biological Examples
Topic: TM Concept Clarification
Replies: 2
Views: 236

Re: TM Concept Clarification

The transition metals act as Lewis acids, accepting the donated electron pair.
Tue Nov 28, 2017 8:03 pm
Forum: Naming
Topic: prefixes
Replies: 2
Views: 183

Re: prefixes

The usual prefixes are bi for 2, tri for 3, tetra for 4, etc. However, if the ligand is polydentate, you use bis for 2, tris for 3, tetrakis for 4 and so on.
Tue Nov 28, 2017 8:02 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changing the Temperature
Replies: 2
Views: 300

Re: Changing the Temperature

When an endothermic reaction is heated, product formation is favored.
When an endothermic reaction is cooled, reactant formation is favored.
When an exothermic reaction is cooled, product formation is favored.
When an exothermic reaction is heated, reactant formation is favored.
Tue Nov 21, 2017 11:42 am
Forum: Hybridization
Topic: Writing Hybridization
Replies: 3
Views: 291

Re: Writing Hybridization

In lecture, Dr. Lavelle mentioned that it does not matter in which order you write them.
Tue Nov 21, 2017 11:39 am
Forum: Hybridization
Topic: Question 4.81
Replies: 2
Views: 211

Re: Question 4.81

Although working with the hybridization of carbon is easy since we know for sure that carbon makes 4 bonds, the hybridization of other elements works in a similar way.
Mon Nov 20, 2017 9:36 pm
Forum: Hybridization
Topic: Homework question #43
Replies: 2
Views: 235

Homework question #43

Can anyone explain the reasoning behind number 43? The question is:
Do you expect the bond angle between 2 hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?
Sun Nov 19, 2017 1:14 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles
Replies: 3
Views: 252

Re: Bond angles

We are only expected to know the general bond angles (such as less than 120, etc) since the exact bond angles can only be determined from experimental observation.
Sun Nov 19, 2017 1:12 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Radicals
Replies: 4
Views: 325

Re: Radicals

From what I understand, there will only be one radical since if there were two, they would combine to form an electron pair.
Sat Nov 11, 2017 9:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle Exceptions
Replies: 3
Views: 584

Re: Bond Angle Exceptions

The exceptions to the bond angles are caused by repulsion by the lone pairs of electrons. In lecture, Dr. Lavelle mentioned that we only had to know what the bond angles should be for most shapes and that we did not have to memorize the exceptions.
Sat Nov 11, 2017 9:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Resonance
Replies: 3
Views: 254

Re: Resonance

Resonance shouldn't have an effect on the shape since technically, a resonant structure is the same structure put together in a different way. However, you should use formal charges to decide on the best lewis structure before you decide on the shape.
Fri Nov 03, 2017 9:12 am
Forum: Resonance Structures
Topic: Lewis Structures: Resonance Hybrid
Replies: 2
Views: 272

Re: Lewis Structures: Resonance Hybrid

The resonance structure in which you can get the most number of FC to equal 0 is the most stable and should be used.
Fri Nov 03, 2017 9:07 am
Forum: Ionic & Covalent Bonds
Topic: Metallic Bond
Replies: 4
Views: 311

Re: Metallic Bond

What is meant by a sea of electrons?
Thu Oct 26, 2017 8:14 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: ch 2, 47, part d
Replies: 2
Views: 257

Re: ch 2, 47, part d

All the transition metals that are in the same group as chromium and copper will want to make both their s and p subshells half full so instead of s2 p4, it will be s1 p5
Thu Oct 26, 2017 8:12 pm
Forum: Trends in The Periodic Table
Topic: 2.67 part B
Replies: 4
Views: 314

Re: 2.67 part B

Generally atoms that have half or full orbitals are the most stable so they will not want to add electrons that easily.
Fri Oct 20, 2017 2:42 am
Forum: Photoelectric Effect
Topic: Rydberg
Replies: 11
Views: 935

Re: Rydberg

The frequency should always be positive, so subtract the bigger number from the smaller number to get a negative number and multiply it by the Rydberg constant times -1.
Fri Oct 20, 2017 2:39 am
Forum: Photoelectric Effect
Topic: Energy of Photon [ENDORSED]
Replies: 9
Views: 1946

Re: Energy of Photon[ENDORSED]

Yes, if the energy of the photon exactly matches the work function of the metal, the electron that is emitted will have zero kinetic energy.
Thu Oct 12, 2017 11:29 pm
Forum: Properties of Electrons
Topic: De Broglie Equation
Replies: 3
Views: 2060

Re: De Broglie Equation

Another common problem concerning the De Broglie Equation is one in which they give you the wavelength and mass and ask you to calculate the speed. In all these problems, they give you 2 of the 3 variables (Planck's constant is known) and you are asked to calculate the third one.
Thu Oct 12, 2017 11:19 pm
Forum: *Black Body Radiation
Topic: Black Body? [ENDORSED]
Replies: 13
Views: 1439

Re: Black Body?[ENDORSED]

The term black body came about since these objects appear black in color at room temperature. They absorb all light and do not reflect any light.
Thu Oct 05, 2017 10:41 pm
Forum: Significant Figures
Topic: Does temperature count for sig figs? [ENDORSED]
Replies: 4
Views: 9459

Re: Does temperature count for sig figs?[ENDORSED]

Assuming you use temperature in your calculations, it does count for sig figs because it is a measurement. In general, anything you measure that does not have 100% accuracy counts for sig figs and any exact values, like conversion factors, do not count for sig figs.
Thu Oct 05, 2017 10:35 pm
Forum: Balancing Chemical Reactions
Topic: Fundamental Exercise H.11
Replies: 2
Views: 289

Re: Fundamental Exercise H.11

Hi, the reason you would start "fresh" is that when you balance an equation, you are simply trying to make sure that for that particular equation, the two sides are in fact equal to each other. When you start with another equation, you do not include any of the stoichiometric coefficients ...

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