## Search found 102 matches

Sat Mar 17, 2018 8:43 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: leaving k or K in derivation of rate of formation of P [ENDORSED]
Replies: 1
Views: 1980

### leaving k or K in derivation of rate of formation of P[ENDORSED]

We know that equilibrium constant K is equal to k/k'. When we are deriving an expression for the rate of formation of product using the pre-equilbrium approach, can we leave the final answer with K (equilibrium constant), or do we have to simplify K to be k/k'? Will we be marked off points if we lea...
Sat Mar 17, 2018 5:38 pm
Forum: Phase Changes & Related Calculations
Topic: Delta T and Sig Figs
Replies: 1
Views: 386

### Delta T and Sig Figs

The first question of the 2015 Final asks you to solve for the specific heat of a substance. The mass is 15.9 g, the initial temperature is 25 degrees C, and the final temperature is 1027 degrees C. When we are rounding off our final answer, what is the correct amount of sig figs we have? I was orig...
Fri Mar 16, 2018 9:56 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: sign of k
Replies: 3
Views: 539

### sign of k

Can the rate constant, k, ever be negative?
Fri Mar 16, 2018 9:12 pm
Forum: Balancing Redox Reactions
Topic: determining cathode from anode
Replies: 11
Views: 774

### determining cathode from anode

If we are given two half reactions with their standard cell potentials, how exactly are we supposed to know which is the cathode and which is the anode, and thus which reaction we would need to reverse? For example on question 3C of the 2014 Final: Fe3+ + e- --> Fe2+ Zn2+ + 2e- --> Zn(s) It says tha...
Fri Mar 16, 2018 8:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 2014 Final 1C
Replies: 1
Views: 239

### 2014 Final 1C

You are trying to find the value for the enthalpy of vaporization, so you use q=mCdeltaT+(1/2)m*deltaHvap I understand how to do the algebra, however, I'm confused where the solutions got (5.4 * 10^-3 kJ/g C) for the value of C
Fri Mar 16, 2018 8:14 pm
Forum: *Nucleophiles
Topic: Functional Groups
Replies: 3
Views: 610

### Functional Groups

We didn't really go too in depth in lecture on functional groups. What exactly would we be expected to know for the final?
Fri Mar 16, 2018 7:52 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Michaelis-Menten rate equation
Replies: 2
Views: 193

### Michaelis-Menten rate equation

We didn't really cover the Michaelis-Menten rate equation in lecture, so will we be expected to know this thoroughly for the final?
Fri Mar 16, 2018 3:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.91
Replies: 1
Views: 171

### 14.91

The question says: A voltaic cell functions only when the electrical circuit is complete. In the external circuit the current is carried by the flow of electrons through a metal wire. Explain how the current is carried through the cell itself. The solution manual says: A negatively charged electroly...
Fri Mar 16, 2018 2:54 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Predicting if a metal will be dissolved in a solution
Replies: 2
Views: 229

### Predicting if a metal will be dissolved in a solution

How do we predict if a metal will be dissolved in a solution?
Fri Mar 16, 2018 2:39 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Importance of electrolytes?..
Replies: 1
Views: 305

### Importance of electrolytes?..

Can someone explain to me what an electrolyte is and when exactly we would need it in our cell? What is the significance?
Thu Mar 15, 2018 11:09 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.85
Replies: 1
Views: 145

### 15.85

How do we know what the correct orientation of the molecules should be when drawing the proposed structures for activated complexes?
Thu Mar 15, 2018 10:20 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Rate determining step
Replies: 2
Views: 213

### Rate determining step

The book says "In some cases the original reaction with a slow rate-determining step may continue in parallel with the catalyzed reaction. However, the rate is determined by the faster path, which governs the overall rate of formation of products." I thought that the rate was determined by...
Mon Mar 12, 2018 3:11 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: rate constant k
Replies: 1
Views: 189

### rate constant k

We know that the equilibrium constant K (capital K) is equal to k/k'. However is rate constant k (lowercase k) equal to k'/k? I was looking in the solution manual for question 15.61, and I wasn't entirely sure where ln(k'/k) came from or how exactly you get to that step. Can someone please clarify t...
Mon Mar 12, 2018 2:56 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.61
Replies: 4
Views: 271

### Re: 15.61

Swetha Sundaram 1E wrote:k would be the rate constant of the forward reaction. k' would be the rate constant of the reverse reaction.

But they don't specify which is the rate constant for the forward reaction and which is the rate constant for the reverse reaction
Mon Mar 12, 2018 2:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.61
Replies: 4
Views: 271

### 15.61

This question gives us two different values for the rate constant of a first-order reaction. One is 0.76 s-1 at 1000 K and the other is 0.87 s-1 at 1030 K. How do we know which value is k and which value is k'? They don't explicitly specify it in the question.
Sun Mar 11, 2018 3:03 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-determining slowest step
Replies: 5
Views: 434

### Rate-determining slowest step

When there are more than 1 elementary steps in a reaction mechanism, how do we determine which one is the slowest step?
Thu Mar 08, 2018 11:15 pm
Forum: First Order Reactions
Topic: Pseudo-First-Order Reaction
Replies: 1
Views: 206

### Pseudo-First-Order Reaction

If we are working with a reaction that does not have an overall order of 1, what should we look for to know that we should turn it into a pseudo-first-order reaction?
Thu Mar 08, 2018 9:32 pm
Forum: General Rate Laws
Topic: Deriving the Rate Laws
Replies: 3
Views: 256

### Deriving the Rate Laws

When we are deriving the rate laws, does it matter whether we use definite or indefinite integrals? Will we be able to come to the same rate law equations if we use either definite or indefinite integrals? When do we know what is appropriate to use/what we should use?
Thu Mar 08, 2018 2:34 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.17
Replies: 6
Views: 567

### 15.17

When we're solving for the order of a reactant in an equation, we usually go about by finding the experiments in the table in which that reactant's concentration changes and where the other reactants are held constant. However, if one of the reactants is independent of the rate, how does this affect...
Tue Mar 06, 2018 1:55 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19a
Replies: 2
Views: 202

### 15.19a

Can someone explain to me how they found the order of reactant B? I know to look at experiments 2 and 3 to solve this. I'm just confused because the solutions manual says that increasing the concentration of B by the ratio 3.02/1.25 increases the rate by (3.02/1.25)^2, so the reaction is then second...
Tue Mar 06, 2018 12:00 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.17
Replies: 1
Views: 181

### 15.17

When we're trying to find the order of each reactant in a reaction, how exactly do we know which experiments we should work with and which ones we shouldn't? For example, when we're trying to solve for the order with respect to B, why can't we use experiments 1 and 3? We clearly see that the concent...
Mon Mar 05, 2018 11:08 pm
Forum: First Order Reactions
Topic: Half-Lives for First Order Reactions
Replies: 2
Views: 297

### Half-Lives for First Order Reactions

Why is it that for a first-order reaction, the half-life of a substance is independent of its initial concentration? Why can the concentration of A be used as its "initial" concentration at any stage of the reaction? Can someone please clarify this?
Thu Mar 01, 2018 8:41 am
Forum: Zero Order Reactions
Topic: Units of k [ENDORSED]
Replies: 13
Views: 719

### Re: Units of k[ENDORSED]

Rate = k[A]^n, where n is the exponent that represents order of the reaction. Concentration is always going to have units of M/L, which is the equivalent to mol.L -1 .s -1 . Be sure to apply the exponent to the units of the concentration as appropriate. You want to isolate k to be alone on one side ...
Thu Mar 01, 2018 8:16 am
Forum: General Rate Laws
Topic: Overall order [ENDORSED]
Replies: 6
Views: 506

### Re: Overall order[ENDORSED]

To find the overall order of a reaction, you can simply add all the individual orders of each reactant in a reaction.
Thu Mar 01, 2018 8:06 am
Forum: General Rate Laws
Topic: 15.3 C
Replies: 8
Views: 886

### Re: 15.3 C

The unique rate of a reaction takes into account the stoichiometric coefficients of a reaction. It is the rate of appearance/disappearance of any species in a reaction divided by its stoichiometric coefficient.
Fri Feb 23, 2018 10:28 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrode
Replies: 4
Views: 380

### Inert Electrode

When do we have to add an inert electrode to a cell diagram?
Fri Feb 23, 2018 1:36 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.41b
Replies: 1
Views: 168

### 14.41b

How do we know that the standard cell potential is 0 in this particular problem?
Fri Feb 23, 2018 1:14 am
Forum: Balancing Redox Reactions
Topic: 14.13c
Replies: 2
Views: 218

### 14.13c

In the cell diagram for part c of question 13 on the homework, why is the right side of the salt bridge written as Cl-(g)|Cl2(g)? Why is it not Cl2(g)|Cl-(g)?
Thu Feb 22, 2018 10:08 pm
Forum: Balancing Redox Reactions
Topic: 14.5a
Replies: 2
Views: 228

### 14.5a

In the full reaction, reactant O3 is in an aqueous state. Why is it that when we are writing the half reaction O, O3 is in a gaseous state?
Thu Feb 22, 2018 9:59 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Variations of Nernst Equation
Replies: 1
Views: 168

### Variations of Nernst Equation

I was looking over some lecture notes on the Nernst Equation and was a little bit confused about something. We learned that E=E°-(2.303RT/nF)logQ. Can someone clarify where the 2.303 value comes from?
Thu Feb 22, 2018 8:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 1
Views: 96

### Cell Diagrams

When writing a cell diagram, does the charge of an ion have to be taken into consideration to determine the order in which components are written? Is Fe3+(aq) always going to be written before Fe2+(aq)? Or does it not matter?
Thu Feb 22, 2018 7:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Hydrogen Electrode
Replies: 1
Views: 133

### Hydrogen Electrode

In the textbook, it says that a hydrogen electrode is denoted H+(aq)|H2(g)|Pt(s) when it is the right hand electrode in a cell diagram and Pt(s)|H2(g)|H+(aq) when it is the left-hand electrode. I don't quite understand why they are listed in that order because with respect to which side it is as an ...
Wed Feb 21, 2018 10:04 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: molar convention for the reaction Gibbs free energy [ENDORSED]
Replies: 1
Views: 111

### molar convention for the reaction Gibbs free energy[ENDORSED]

Is there anything significant that changes in our calculations if we use the molar convention for finding the reaction Gibbs free energy?
Mon Feb 19, 2018 4:01 pm
Forum: Balancing Redox Reactions
Topic: oxidation numbers of transitional metals
Replies: 1
Views: 176

### oxidation numbers of transitional metals

In determining the oxidation numbers of transitional metals, does it all just depend on the charges of the other atoms it forms a molecule with? Like for example, in the compound MnO 4 - , does the 7+ charge depend solely on the oxygen charges? Do we rely on the non-transitional metals in an ion as ...
Wed Feb 14, 2018 3:04 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Choosing Cp or Cv [ENDORSED]
Replies: 3
Views: 306

### Choosing Cp or Cv[ENDORSED]

When it is not explicitly stated in the question whether pressure or volume are constant, when do we know which to use?
Tue Feb 13, 2018 11:18 pm
Forum: Phase Changes & Related Calculations
Topic: Specific heat of water or ice?
Replies: 6
Views: 489

### Specific heat of water or ice?

When we're calculating questions involving solving for q (heat transfers), I'm a little bit confused on when we would use the specific heat of ice and when we would use the specific heat of water - for questions involving phase changes where ice melts.
Tue Feb 13, 2018 11:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H=Delta U
Replies: 1
Views: 2279

### Delta H=Delta U

Under what circumstances would delta H be equal to delta U? Can someone explain this? In the notes we wrote that the volume of the reactants would be equal to the volume of the products if pressure was constant. However, I still don't get how delta H then becomes equal to delta U
Tue Feb 13, 2018 10:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Boiling point at room temperature
Replies: 5
Views: 308

### Re: Boiling point at room temperature

I was wondering the same question. Saw this exact same concept applied to a question on the 2015 Winter Midterm
Tue Feb 13, 2018 8:57 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Examples of Change Values = 0
Replies: 1
Views: 125

### Examples of Change Values = 0

Can someone give some important to remember examples of the following?

When:
a) Delta S=0
b) Delta G=0
c) Delta U=0
Tue Feb 13, 2018 8:09 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp or Cv in temperature change
Replies: 3
Views: 529

### Cp or Cv in temperature change

When there is a temperature change and we are being asked to solve for delta S, how do we know whether to use Cp or Cv?
Tue Feb 13, 2018 8:35 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible Expansion
Replies: 1
Views: 159

### Reversible Expansion

Can pressure not be constant when reversible expansion is taking place?
Mon Feb 12, 2018 8:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units of Delta H
Replies: 2
Views: 474

### Units of Delta H

Can someone clarify to me when we use the units of kJ/mol for delta H versus when we use just kJ for delta H?
Sun Feb 11, 2018 8:50 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Finding Temperature Where Reaction is Spontaneous
Replies: 2
Views: 186

### Finding Temperature Where Reaction is Spontaneous

Why do we have to set delta G equal to zero when we are trying to find the temperature at which a reaction is spontaneous? I just find this a little confusing because I typically associate spontaneous reactions with negative values for delta G
Sat Feb 10, 2018 10:57 pm
Forum: Calculating Work of Expansion
Topic: Degeneracy [ENDORSED]
Replies: 2
Views: 219

### Degeneracy[ENDORSED]

Can someone explain/clarify what exactly degeneracy is and what its overall importance is?
Sat Feb 10, 2018 5:27 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: units conversion for entropy
Replies: 6
Views: 361

### Re: units conversion for entropy

Usually, the units for entropy are J/K. However, it shouldn't really matter. One thing to be mindful of, though, is keeping your units consistent throughout your calculations. Let's say you are adding up different values for entropies. You want to make sure you are adding entropies that all have uni...
Sat Feb 10, 2018 5:23 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: When to use + sign
Replies: 11
Views: 546

### Re: When to use + sign

Using a + or - sign in your calculations allows you to keep track of something that is either being gained or being lost, especially for problems that ask you to solve for any delta values.
Thu Feb 08, 2018 6:55 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.33
Replies: 2
Views: 201

### 9.33

In part c of 33, the chemical reaction is SO 2 (g) + Br 2 (g) +2H 2 O(l) --> H 2 SO 4 (aq) + 2HBr(aq) Entropy decreases in this reaction. The solution manual says that entropy decreases because the total number of moles decreases. However, like in previous problems, is it sufficient to say that entr...
Sun Feb 04, 2018 8:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: sign of q
Replies: 7
Views: 504

### Re: sign of q

The sign of delta S depends on the direction of heat flow. Delta S is simply qrev divided by T. qrev is negative whenever the system is losing heat. From that information, you then know that the surroundings gain heat. If the system is gaining heat, then qrev is positive.
Thu Feb 01, 2018 1:28 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 3
Views: 228

### 9.13

Whenever a question states that we should assume ideal gas behavior, are we always supposed to plug in 1.00 mol of gas into an equation when the amount of moles is not given? Are there certain circumstances (other than when they actually give us the amount in moles of gas) where we should not automa...
Wed Jan 31, 2018 7:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Celsius or Kelvin
Replies: 5
Views: 342

### Celsius or Kelvin

If asked to calculate the changes in entropy and we are given temperature in terms of Celsius, do we always have to convert the temperature to be in terms of Kelvin? I know both can technically be considered correct, but is there a preferred method?
Thu Jan 25, 2018 11:15 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Superheating
Replies: 3
Views: 244

### Superheating

Do we have to be familiar with superheating for the Week 3 test?
Thu Jan 25, 2018 8:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 1
Views: 122

### Re: 8.67

Update: found my mistake, I had an error in one of the digits
Thu Jan 25, 2018 8:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 1
Views: 122

### 8.67

I'm a little bit confused as to how the solution manual came up with the value of \Delta H= -242 kJ/mol in part a of 8.67. I understand that to find the enthalpy of the reaction, you need to use the equation of bonds broken-bonds formed. I still can't seem to get that same value though. Can someone ...
Thu Jan 25, 2018 7:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49
Replies: 2
Views: 208

### 8.49

For problem 8.49 on the homework, I am a little bit confused on how to first approach the problem. The solution manual starts solving the question using the approach of the PV=nRT equation. However, how do we know just based on the wording of the question that there is a net production of one mole o...
Thu Jan 25, 2018 2:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: The sign of q
Replies: 5
Views: 403

### The sign of q

For questions involving heat transfers between a system and its surroundings, I'm a little bit confused on how you determine where the negative sign goes (which q is going to take the negative sign). If q is negative, doesn't it mean that the temperature is going down, meaning it is losing heat? And...
Thu Jan 25, 2018 2:16 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Expansion
Replies: 3
Views: 290

### Irreversible Expansion

I know that Dr. Lavelle went over this in lecture yesterday a little bit, but can someone please explain to me exactly what an irreversible expansion is? And why is it irreversible? If I understand this correctly, I know that a reversible expansion can be reversed through an infinitesimal change (sm...
Sun Jan 21, 2018 8:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.75 part b
Replies: 3
Views: 216

### 8.75 part b

CH 3 CHCH 2 (g) + H 2 O(g) --> CH 3 CH(OH)CH 3 (g) I understand which bonds are broken and why (because I drew out the Lewis structures). However, for the bonds that are formed from this reaction, I am confused as to why the solution manual says that 1 mol of a C-C SINGLE bond is formed. Also, it sa...
Sun Jan 21, 2018 7:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Intensive vs. Extensive Properties
Replies: 4
Views: 242

### Intensive vs. Extensive Properties

I'm having a little bit of trouble distinguishing the differences between intensive and extensive properties. We were told that extensive properties are dependent on the amount of a substance, so one could imply that intensive properties would be the opposite. However, how are intensive properties n...
Sun Jan 21, 2018 4:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units of Standard Enthalpies of Formation
Replies: 2
Views: 158

### Units of Standard Enthalpies of Formation

I know that the units of standard enthalpies of formation is always kJ/mol. However, for problem 8.63 in the textbook solutions manual, why is the solution only given in kJ and not kJ/mol? Are there certain instances where the answer should only be written with units of kJ? Should we just stick to a...
Sun Jan 21, 2018 2:52 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.25
Replies: 1
Views: 119

### 8.25

When calculating q for the calorimeter, why are you multiplying it by 2.49 K and not 7.32 K? How do you know which value to use?
Sat Jan 20, 2018 7:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat not being a state property..
Replies: 1
Views: 74

### Heat not being a state property..

We know that the change in enthalpy is equal to q p , and we also know that enthalpy is a state property. However, we were taught in lecture that heat, which is q,is not a state property because it depends on the path it was taken to get to its final state. How is it not a state property when the ch...
Thu Jan 18, 2018 2:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Knowing which equation to use when finding q
Replies: 2
Views: 191

### Knowing which equation to use when finding q

We've seen so many different equations that can be used to calculate q such as q=nCdeltaT or q=mCdeltaT. How do we know when to not take mass or moles into account and just use the equation q=C*deltaT? I was having a hard time finding why this equation was used in 8.53 when a mass was given.
Thu Jan 18, 2018 2:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 1
Views: 129

### 8.51

For homework problem 8.51, I understand how to come up with the calculation formatting, but I'm a bit confused with the signs of some of the values in the solutions manual. Can someone explain the reason the final answer is +23.9x10^3 kJ/L, a positive value? Energy is being released so I would origi...
Wed Jan 17, 2018 11:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45
Replies: 1
Views: 86

### 8.45

How exactly are we supposed to approach part c in homework problem 8.45?
4 C(s) + S8(s) --> 4 CS2(l) deltaH=+358.8 kJ
c) If the heat absorbed in the reaction was 415 kJ, how much CS2 was produced?
Wed Jan 17, 2018 3:39 pm
Forum: Phase Changes & Related Calculations
Topic: Accounting for mass in phase changes
Replies: 2
Views: 244

### Accounting for mass in phase changes

For questions such as homework problem 8.41, where you are asked to calculate enthalpy changes where phase changes are involved, how do you know when to account for the molecular weight of a substance? In other words, if you are given the mass of a substance, how exactly do you know when to divide t...
Wed Jan 17, 2018 12:21 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework 8.29
Replies: 5
Views: 287

### Re: Homework 8.29

NO2 is more complex than NO considering it has one more atom in it. This makes the molecule more complex. Since there are more atoms present, there is room for more energy to be absorbed, hence a larger capacity for heat.
Wed Jan 17, 2018 12:18 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW 8.31
Replies: 1
Views: 116

### HW 8.31

When asking to calculate the amount of heat released, how do we find what the heat capacities are for the Kr gas? I understand that to find the amount of heat released, the formula is mass x heat capacity x change in temperature. I have mass and the change in temperature, but how do I find the heat ...
Thu Jan 11, 2018 7:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity vs. Specific Heat Capacity
Replies: 6
Views: 323

### Re: Heat Capacity vs. Specific Heat Capacity

Heat capacity refers to the amount of heat that is required to change the temperature of an object by a certain degree. Specific heat capacity, however, refers amount of heat that is required to raise the temperature of an object per unit mass. In other words, you can obtain that by dividing the hea...
Thu Jan 11, 2018 7:09 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature during phase changes [ENDORSED]
Replies: 4
Views: 404

### Re: Temperature during phase changes[ENDORSED]

This is because the energy being supplied in the form of heat disrupts the INTERmolecular forces that hold the liquid or solid together. Nothing is happening intramolecularly.
Thu Jan 11, 2018 2:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law vs. Using Bond Enthalpies
Replies: 3
Views: 319

### Hess's Law vs. Using Bond Enthalpies

What are the ultimate differences between the two methods we were taught in lecture yesterday to calculate change in enthalpies? The first was Hess's Law and the other was using the bond enthalpies. I was trying to watch videos online to clarify this concept but was a little confused. Where does the...
Sat Dec 09, 2017 5:58 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: if [H3O+] is less than 10^-7
Replies: 1
Views: 537

### if [H3O+] is less than 10^-7

Can someone please re-explain/clarify why it is that the solution is still considered neutral even when [H3O+] < 10^-7 ? How exactly does this concept tie in with the reasoning that autoprotolysis generates 10^-7 mol/L ?
Sat Dec 09, 2017 3:44 pm
Forum: Biological Examples
Topic: #21 on Practice Final
Replies: 2
Views: 305

### #21 on Practice Final

For those of you who went to the review session last night to go over the questions on the practice final, could you explain #21 to me? We are being asked to find the oxidation state of iron in the heme complex. In order to find it, we must find the formal charges of the nitrogen atoms. He demonstra...
Sat Dec 09, 2017 3:04 pm
Forum: Lewis Structures
Topic: NO2 Lewis Structure
Replies: 2
Views: 856

### NO2 Lewis Structure

Why is NO2 not drawn with two double bonds? If it is drawn with two double bond and one lone electron on the N central atom? Wouldn't all the formal charges of the atoms be 0 if it was drawn that way? if it's drawn with two single bonds and one double bond, there would be formal charges on the N ato...
Sat Dec 09, 2017 2:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of I-
Replies: 1
Views: 138

### Electron Configuration of I-

For the ground-state electron configuration of I-, is it acceptable/correct on a test to answer it as simply [Xe]? Or is it preferred to write [Kr]4d10,5s2,5p6 (without the commas, of course)? Or are both acceptable?
Wed Dec 06, 2017 2:02 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Using ICE table for calculating pH or pOH? [ENDORSED]
Replies: 1
Views: 280

### Using ICE table for calculating pH or pOH?[ENDORSED]

Since we know that strong acids and strong bases are completely ionized in water unlike weak acids and bases, when we are calculating for pH and pOH in reactions that involve strong acids or bases, is it necessary to set up an ICE box? Like we do when solving for concentrations involving weak acids ...
Wed Dec 06, 2017 12:20 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Relative Acidity
Replies: 3
Views: 517

### Re: Relative Acidity

The CCl3 group in trichloroacetic acid that is bonded to the carboxyl group, -COOH, is more electronegative (electron-drawing) than the CH3 group in acetic acid that is bonded to the carboxyl group. With respect to the definition of a Lewis acid, an electron acceptor, this would make CCl3 more acidi...
Tue Dec 05, 2017 3:18 pm
Forum: Lewis Acids & Bases
Topic: Determining stronger acids
Replies: 1
Views: 168

### Determining stronger acids

When you are comparing HCLO4 and H3PO4 to determine which one is a stronger acid, you know right away that Cl is more electronegative than P. However, does the number of H atoms in the molecule affect its strength in acidity? There is the same number of O atoms, but there is a different number of H ...
Tue Dec 05, 2017 2:58 pm
Forum: Lewis Acids & Bases
Topic: 12.49
Replies: 2
Views: 252

### 12.49

Question 12.49 on the homework says: Which is the stronger base, the hypobromite ion, BrO- , or morphine, C17H19O3N? Justify your answer. The answer to the question is that the stronger base is the hypobromite ion. I understand that for oxoacids, the more oxygen atoms there are in a compound, the st...
Mon Dec 04, 2017 10:04 pm
Forum: Lewis Acids & Bases
Topic: 12.27
Replies: 1
Views: 177

### 12.27

I don't understand how to solve part b of #27 on the chapter 12 homework. Can someone explain how they went about to setup the calculation for part b? I didn't quite get how they did it in the solution manual A careless laboratory technician wants to prepare 200.0 mL of a 0.025 m HCl(aq) solution, b...
Mon Dec 04, 2017 9:32 pm
Forum: Lewis Acids & Bases
Topic: Classifying Oxides as Amphoteric
Replies: 3
Views: 263

### Classifying Oxides as Amphoteric

I understand that if an oxide is amphoteric, it can react with both acids and bases. However, how can you tell just by looking at a chemical formula whether that molecule will be amphoteric or not. For example, in question 12.17d, how are you able to tell that Bi2O3 is amphoteric and not simply basi...
Sun Dec 03, 2017 11:53 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: J5. Complete Ionic Equations
Replies: 1
Views: 171

### J5. Complete Ionic Equations

As I was working through some of the problems in Fundamentals J of the textbook, I was doing some questions involving writing out the complete and net ionic equations of particular reactions. When writing out ionic equations, how do we know when exactly to split up a molecule into its particular ato...
Sun Dec 03, 2017 11:16 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Weak Acids / Strong Acids
Replies: 5
Views: 405

### Re: Weak Acids / Strong Acids

The easier it is for the acid to dissociate, the stronger of an acid it is. Keep in mind that single arrows are used in chemical reactions for strong acids to denote that it is being COMPLETELY ionized when it is in water. Stronger acids can donate more protons in comparison to weak acids because th...
Tue Nov 28, 2017 10:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc vs. Kp
Replies: 3
Views: 340

### Kc vs. Kp

When we are asked to write the equilibrium expression K for a reaction and we are not told whether to write that equation with respect to concentration or partial pressures, how do we know which way to write the expression? In question 11.3 on the homework, I originally answered it in terms of molar...
Sun Nov 26, 2017 11:51 am
Forum: Naming
Topic: naming order of things outside the bracket
Replies: 2
Views: 204

### Re: naming order of things outside the bracket

I was confused at first as well when I encountered some of the questions on the homework. Then I realized that the cation always precedes the coordination sphere and the anion always proceeds the coordination sphere. To think of it in simpler terms, think of a compound as simple as NaCl - the cation...
Sat Nov 25, 2017 3:47 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determining how many binding sites a ligand has
Replies: 1
Views: 129

### Determining how many binding sites a ligand has

At face-value, it is not too difficult to determine whether or not a ligand has more than one binding site for electrons. This is because we are pretty familiar with drawing Lewis structures and taking lone pairs of electrons into consideration. However, I'm a little bit confused when it comes to de...
Sun Nov 19, 2017 8:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent or linear?
Replies: 11
Views: 1009

### Re: Bent or linear?

It would be linear if there are no lone pairs of electrons on the central atom. This is because the lone pairs are responsible for any repulsion between themselves and the bonded electrons. The bent shape/structure of any molecule can be attributed to this repulsion phenomenon. A linear shape would ...
Sun Nov 19, 2017 8:30 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Difference Between Sigma and Pi Bonds [ENDORSED]
Replies: 4
Views: 963

### Difference Between Sigma and Pi Bonds[ENDORSED]

What exactly is important for us to know when it comes to differentiating between sigma and pi bonds? I understand that sigma bonds are known as every first bond between two atoms, and a pi bond is every second or third bond, etc between two atoms. In lecture we were taught that sigma bonds are when...
Sun Nov 12, 2017 4:48 pm
Forum: Electronegativity
Topic: electronegativity chart
Replies: 11
Views: 945

### Re: electronegativity chart

The definition of electronegativity itself is "the electron-pulling power of an atom." The best way to think of it conceptually without having to memorize any numbers is to think of it in terms of electron affinity. The trend for electron affinity increases as you go from left to right acr...
Fri Nov 10, 2017 11:40 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and stability [ENDORSED]
Replies: 7
Views: 4346

### Re: Formal Charge and stability[ENDORSED]

You should aim to draw a Lewis structure with atoms with a formal charge as close to zero as possible. When you add all the formal charges of each of the atoms together, you get the overall formal charge of the compound itself. Lower formal charges correspond to more stability within those compounds...
Sun Nov 05, 2017 3:55 pm
Forum: Dipole Moments
Topic: Conventions for representing dipoles [ENDORSED]
Replies: 1
Views: 157

### Conventions for representing dipoles[ENDORSED]

In the textbook, it says that the modern convention for representing a dipole (which is used throughout the book) is having an arrow point toward the positive partial charge. In the original convention, a dipole is represented with an arrow pointing toward the negative partial charge. In lecture, we...
Wed Nov 01, 2017 7:15 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Exceptions to Electron Configurations
Replies: 1
Views: 166

### Exceptions to Electron Configurations

Upon doing some of the practice problems and looking at the solutions manual, I saw that Tungsten didn't follow the same exceptions rule as copper and chromium do when it comes to electron configuration. You would originally think that you would leave make the d shell half-filled and leave the s orb...
Wed Nov 01, 2017 12:03 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Homework 2.43
Replies: 4
Views: 365

### Re: Homework 2.43

To answer the first question, the reason the electron configuration for silver is [Kr]4d^10 5s^1 instead of [Kr]4d^9 5s^2 is because when you are one electron away from a half-full or fully d shell, it is actually lower in energy to fully fill the d shell and to leave the s orbital singly occupied w...
Fri Oct 27, 2017 2:05 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Shells, Subshells, and Orbitals
Replies: 4
Views: 443

### Re: Shells, Subshells, and Orbitals

The above responses are great, but to elaborate on orbitals, orbitals can be thought of in terms of probability density. Instead of thinking of electrons as moving around in an orbit, meaning only round and round in a 2D flat space, think of the possible area (in terms of volume) that an electron ca...
Tue Oct 24, 2017 2:56 am
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Quantum Numbers & Orbital Orientation
Replies: 1
Views: 331

### Magnetic Quantum Numbers & Orbital Orientation

I understand that the allowed values for the magnetic quantum number range from l,l-1,...-l, but once we solve what those values are, what exactly do those numbers tell us? I know that the magnetic quantum number labels different orbitals of a subshell in terms of their orientation, but how does the...
Tue Oct 17, 2017 10:40 pm
Forum: DeBroglie Equation
Topic: Detecting wavelength and observing wavelike characteristics
Replies: 1
Views: 189

### Detecting wavelength and observing wavelike characteristics

Is there a particular "threshold" in length that a wavelength must have in order for us to be able to detect the wavelength or observe its characteristics? What is considered "too small" for us to detect?
Tue Oct 17, 2017 9:09 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post Module #42
Replies: 3
Views: 303

### Atomic Spectra Post Module #42

Can someone help me with how to solve this problem? The question reads, "An excited hydrogen atom emits light with a frequency of 1.14 x 1014 Hz to reach the energy level n = 4. In what principle quantum level did the electron begin?"
Tue Oct 17, 2017 2:36 pm
Forum: Photoelectric Effect
Topic: 1.33 Part A
Replies: 4
Views: 359

### Re: 1.33 Part A

Use the equation that directly includes wavelength, since that is the quantity you are looking for. The Ek formula should be utilized when you are looking for mass, velocity, or excess energy electron
Mon Oct 16, 2017 1:33 am
Forum: Photoelectric Effect
Topic: Kinetic energy equal to zero?
Replies: 4
Views: 1035

### Re: Kinetic energy equal to zero?

If the energy of the photon is equal to the threshold energy, then there will be no excess energy. All kinetic energy from the electron is attributed to excess energy of the incoming photon. If there's no kinetic (excess) energy, then no electron will be ejected. Therefore, when you're looking at wo...
Mon Oct 16, 2017 1:23 am
Forum: Properties of Light
Topic: Converting Units [ENDORSED]
Replies: 11
Views: 809

### Re: Converting Units[ENDORSED]

It might be easier to calculate and see the final answer in meters. However, when asked to compare with other wavelengths, and with questions that ask for different types of radiation, converting your answer to to units of nanometers in the end is very helpful.
Tue Oct 10, 2017 10:13 pm
Forum: Properties of Light
Topic: Rydberg's Formula
Replies: 3
Views: 492

### Rydberg's Formula

In the video module under "Atomic Spectra," it discusses how electrons continually become "more negative" when they go down energy levels and emit more photons. When discussing Rydberg's formula, we were given -R=[(1/n1^2)-(1/n2^2)]. In the book, the same formula is given but jus...