## Search found 64 matches

Thu Mar 15, 2018 1:07 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 2
Views: 190

### Catalysts

15.73
Why are catalysts NOT consumed in course of reaction? I thought it had to be consumed in order to make the reaction happen
How come the catalyst does not affect Equilibrium?
Tue Mar 13, 2018 7:11 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Which is which k?
Replies: 4
Views: 268

### Which is which k?

How do you know which is k' or k if the homework problem doesn't specify which is the forward or reverse reaction??
Mon Mar 12, 2018 10:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.33
Replies: 2
Views: 351

### 14.33

a) The standard Gibbs free energy of formation of Tl3(aq) is 215 kJmol1 at 25 C. Calculate the standard potential of the Tl3/Tl couple. (b) Will Tl disproportionate in aqueous solution? Why did they reverse the reaction in the solutions? is it so that the gibbs free would become negative? how do we ...
Mon Mar 12, 2018 8:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 253

### Cell Diagram

under what conditions do we use a Pt in the cell diagram?
Sun Mar 11, 2018 10:35 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G at Boiling Point
Replies: 3
Views: 2097

### Delta G at Boiling Point

why is gibbs free energy zero at 100 boiling point (number 9.91)
Sat Mar 10, 2018 12:52 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.53
Replies: 3
Views: 355

### 8.53

8.53 The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113 C to 22.799 C. The calorimeter assembly is known to have a total heat capacity of 3.00 kJ·(...
Fri Mar 09, 2018 11:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.25
Replies: 1
Views: 294

### 8.25

Problem is: A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q3.50 kJ), resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq...
Sun Mar 04, 2018 7:32 am
Forum: First Order Reactions
Topic: 15.23
Replies: 4
Views: 289

### 15.23

For Part C, why did you have to subtract (2(.034molB)) from (.153 molA) to get [A]t, I thought calculating [A]t would only require multiplying .034molB by 2?
Sat Mar 03, 2018 9:18 pm
Forum: Second Order Reactions
Topic: 15.19
Replies: 2
Views: 178

### 15.19

How do you find the order of reaction for [B] if the A and C concentrations do not stay constant from one experiment to the next?
Fri Mar 02, 2018 10:33 am
Forum: First Order Reactions
Topic: Pseudo First Order Reaction
Replies: 5
Views: 719

### Pseudo First Order Reaction

What is the difference between Pseudo and regular first order reaction?
Wed Feb 28, 2018 5:24 pm
Forum: General Rate Laws
Topic: Negative Signs [ENDORSED]
Replies: 6
Views: 506

### Negative Signs[ENDORSED]

Whenever we have to find a rate, is it always going to be positive by using the absolute value of change in [R]? When is it negative?
Mon Feb 26, 2018 1:32 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated [ENDORSED]
Replies: 3
Views: 446

### Isolated[ENDORSED]

Why is the universe isolated?
Mon Feb 26, 2018 1:28 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q4A [ENDORSED]
Replies: 4
Views: 333

### Midterm Q4A[ENDORSED]

A piston containing 0.10 mol of nitrogen gas at 298 K has an initial volume of 2.24 L and
undergoes an expansion against 0.5 atm external pressure until its volume doubles.
Calculate the work involved in Joules.

How come in this question you can assume constant P?
Mon Feb 26, 2018 1:26 pm
Forum: General Rate Laws
Topic: Half Rxns [ENDORSED]
Replies: 2
Views: 169

### Half Rxns[ENDORSED]

In lecture, it was mentioned that the compound with the longest half life is the most stable, why is that?
Sun Feb 18, 2018 5:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11
Replies: 2
Views: 235

### 14.11

When comparing the Ecell, how do you know which is the cathode or anode?
Sun Feb 18, 2018 4:30 pm
Forum: Balancing Redox Reactions
Topic: 14.5A
Replies: 1
Views: 208

### 14.5A

The directions are to balance the redox reaction in basic solution. A. Action of ozone on bromide ions, O3 (aq) + Br - (aq) --> O2 (g) + BrO3 - (aq).

Why does the solutions manual switch it to 02-> 03? how do you know its the Oxygen and not BR that is reduced?
Sun Feb 18, 2018 1:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells 14.3
Replies: 2
Views: 164

### Galvanic Cells 14.3

The textbook says the current produced can be used to electrical work but it also says although energy is released as heat, there is no electrical work done. So which is it? or what do we need to understand about electrical work conceptually in the galvanic cell context?
Sat Feb 10, 2018 4:20 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Temperature
Replies: 1
Views: 163

### Temperature

For the formula delta = qrev/t the text book says that the temperature is absolute, does that mean that the temperature has to be an absolute value (not negative) or did it mean at a specific no change temperature
Sat Feb 10, 2018 2:25 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Units Cancel
Replies: 1
Views: 151

### Units Cancel

for delta S=nRln(p1/p2) we don't have to convert the Kpa to atm because the units will cancel but would it matter for temperature? does it always have to be in kelvin when in ln? does the same thing apply for delta G= -rtlnK?
Fri Feb 09, 2018 1:04 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 9.47
Replies: 1
Views: 177

### 9.47

How can delta S total have a value if delta S surroundings is 0? If there isnt any heat transferred into surroundings and the entropy is unchanged then what does the delta S total numeric value stand for conceptually?
Thu Feb 08, 2018 10:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.73
Replies: 1
Views: 154

### 8.73

How do you know if you need to break a bond or not? For example in 8.73 you didnt need to break the c-h
Mon Feb 05, 2018 8:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Stability
Replies: 1
Views: 93

### Stability

How can the sign of delta G at standard state tell us whether a compound is stable or not? if the delta G is positive is the compound stable or unstable?
Wed Jan 31, 2018 8:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Total Enthalpy
Replies: 2
Views: 185

### Total Enthalpy

How come if the reaction is reversible expansion, the Stotal is 0? but for an irreversible expansion there is a value for Stotal?
Wed Jan 31, 2018 7:33 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: 9.35
Replies: 1
Views: 148

### 9.35

How come container A's entropy is higher than container C's entropy. Container A's atoms are monatomic while C's atoms are diatomic. If they're diatomic, doesn't it make it a bit more complex?
Wed Jan 31, 2018 7:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Residual Entropy
Replies: 1
Views: 142

### Residual Entropy

What is the concept behind residual entropy?
Mon Jan 29, 2018 5:36 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equations
Replies: 2
Views: 184

### Equations

For the first few problems of Chapter 9, the solutions derived the equations, will we be expected to know how to for exams?
Tue Jan 23, 2018 7:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exothermic
Replies: 7
Views: 397

### Exothermic

how come when a system's temperature increases, it mean that it is exothermic? wouldn't be endothermic since its temperature went up meaning it absorbed heat?
Mon Jan 22, 2018 11:53 pm
Forum: Phase Changes & Related Calculations
Topic: Specific heat capacity
Replies: 3
Views: 236

### Specific heat capacity

to clarify in general terms, if substance 1 has a smaller specific heat capacity compared to substance 2, does that mean substance one requires less heat or less of something to change its temperature?
Sat Jan 20, 2018 3:53 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature [ENDORSED]
Replies: 2
Views: 128

### Temperature[ENDORSED]

When does it matter or in what type of problems do we need to use either Kelvin or degrees Celsius? For example, problem chapter 8 #31 R= 8.314J/k.mol but the problem gives you the temperature in degrees celsius, do we need to convert the degrees celsius into kelvin to cancel out the temperature?
Sat Jan 20, 2018 9:05 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 4
Views: 178

### Enthalpy

What is the difference between bond enthalpies and enthalpies of formation? When do we use each?
Mon Jan 15, 2018 4:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Trends
Replies: 2
Views: 204

### Enthalpy Trends

What does it mean if a bond has a greater enthalpy than another? does it mean it is more stable?
Thu Jan 11, 2018 5:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 3
Views: 179

### 8.51

Chapter 8 problem 51: Why is the answer positive? and How do you get the enthalpy for carbon and water?
Thu Jan 11, 2018 4:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49
Replies: 5
Views: 241

### 8.49

in chapter 8 problem 49, how did you know the temperature to calculate work was 298K? and why was there a negative sign ?
Thu Jan 11, 2018 3:01 pm
Forum: Phase Changes & Related Calculations
Topic: Ideal Gas
Replies: 5
Views: 297

### Ideal Gas

What does it mean when something behaves as an ideal gas? why is that significant for problem 8.31?
Wed Jan 10, 2018 9:46 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes
Replies: 2
Views: 196

### Phase Changes

The enthalpy of sublimation of a substance must be = to the sum of the enthalpies of fusion and vaporization, "provided that they are measured at the same temperature". Regarding the temperature part of this statement, does that mean all enthalpies are at the same temperature? or what's th...
Thu Dec 07, 2017 11:14 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Strong Bases
Replies: 1
Views: 207

### Strong Bases

On the pH scale I thought the strongest base would be at 14 but how come the book states that "the weaker the base, the smaller the value of Kb and the greater the value of pKb"? Don't these two ideas contradict one another?
Mon Dec 04, 2017 9:59 pm
Forum: Bronsted Acids & Bases
Topic: ch 12 #33
Replies: 1
Views: 169

### ch 12 #33

For part B, why would finding the original solution involve dividing the diluted solution by transferred solution ... 500ml/5ml?
Mon Dec 04, 2017 9:31 pm
Forum: Bronsted Acids & Bases
Topic: Ch 12 #27
Replies: 2
Views: 231

### Ch 12 #27

How come for part B of the question the solution would be (200 mL x .025M HCL)/ (250ml)
why do you multiple the M and the volume and then divide by the other volume? What's the conceptual idea behind this
Sun Dec 03, 2017 9:31 pm
Forum: Dipole Moments
Topic: Dipole Moments
Replies: 2
Views: 302

### Dipole Moments

If there is an imbalance in formal charges, does that mean there is a dipole moment or would there only be a dipole moment is there are lone pairs on the central atom? also, what characterizes something to be the biggest dipole?
Sun Dec 03, 2017 12:05 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic/Endothermic [ENDORSED]
Replies: 2
Views: 1643

### Exothermic/Endothermic[ENDORSED]

How do you know if a reaction is exothermic or endothermic without being told?
Mon Nov 27, 2017 5:31 pm
Forum: Naming
Topic: Alphabetical Order
Replies: 2
Views: 174

### Alphabetical Order

In the naming compounds pdf from the website, the formula for tetra-ammine-chloro-nitro-cobalt(III0-chloride is {Co(NH3)4(NO2)CL}Cl, how come the NH3/NO2 come before CL? shouldn't CL come before both due to alphabetical order rule?
Mon Nov 27, 2017 5:10 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ch 11 #39
Replies: 1
Views: 142

### Ch 11 #39

I understand where the two K come from but why do you multiply them?
Sun Nov 26, 2017 5:55 pm
Forum: Naming
Topic: CH 17 #31
Replies: 1
Views: 170

### CH 17 #31

for part D the answer is Na {Fe (OH2)2(C2O4)2} Why is OH2 before C2O4? I thought they had to be in alphabetical order
Fri Nov 24, 2017 11:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ch 11 #47
Replies: 1
Views: 138

### Ch 11 #47

When finding the percentage of PCl5 that has decomposed at equilibrium why couldn't we divide .009 ([PCl5] at equilibrium)/.019? why did the solutions round .009 to .01? Not rounding would give 47% but rounding would give 53%? it's a pretty big difference, would it matter if we rounded or not?
Thu Nov 23, 2017 5:50 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Equilibrium Composition
Replies: 4
Views: 428

### Equilibrium Composition

When calculating Equlibrium Composition when do we know to approximate or use the quadratic equation? And in approximation, what are we approximating?
Tue Nov 21, 2017 9:21 pm
Forum: Coordinate Covalent Bonds
Topic: Ch 17 #29
Replies: 2
Views: 555

### Ch 17 #29

For CN minus, the name is cyanido but how come the answer for part C is aquapentaCYANOcobaltate(III) ion? When do we use cyano and when do we use cyanido?
Mon Nov 20, 2017 6:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ch 11 # 1
Replies: 2
Views: 211

### Ch 11 # 1

Why is it TRUE that if one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger?

If K= Concentration of P/ Concentration of R, if the concentration of R is higher wouldn't it make the overall concentration of P smaller?
Mon Nov 13, 2017 9:04 pm
Forum: Hybridization
Topic: Ch4 #43
Replies: 1
Views: 158

### Ch4 #43

What does it mean when the S- character of a hybrid orbital increases?
Mon Nov 13, 2017 9:03 pm
Forum: Hybridization
Topic: Ch 4 #95
Replies: 2
Views: 177

### Ch 4 #95

How come in the answers the hybridization includes numbers like 1 and 2. For example, Carbon's hybridization is 2sp^2. what does the first 2 stand for or mean?
Mon Nov 13, 2017 4:13 pm
Forum: Lewis Structures
Topic: Bond Lengths [ENDORSED]
Replies: 3
Views: 299

### Re: Bond Lengths[ENDORSED]

I think that the sum of two single bonds is stronger than a double bond; therefore, it is probably shorter or about the same length.
Fri Nov 03, 2017 11:56 pm
Forum: Trends in The Periodic Table
Topic: chapter 3, 77
Replies: 1
Views: 178

### chapter 3, 77

how do you know that HCL is more ionic than HI, CF4 is more ionic than CH4, and CO4 is more ionic than CS2 if we didn't have the electronegativity of these elements memorized? also HI, CH4, and CS2 are farther apart on periodic table so I thought those would be more ionic.
Mon Oct 30, 2017 11:10 pm
Forum: Trends in The Periodic Table
Topic: Chapter 2, #93
Replies: 3
Views: 257

### Chapter 2, #93

How come Na becomes a larger circle and Cl is a smaller circle? how do the charges come into play?
Mon Oct 30, 2017 11:06 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ions
Replies: 2
Views: 253

### Ions

If a question asks to write the electron for an ion like Tin(IV). How do you know if it is an anion or cation aka Sn4- or Sn 4+
Sun Oct 29, 2017 11:46 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Chapter 2, #43 [ENDORSED]
Replies: 3
Views: 365

### Chapter 2, #43[ENDORSED]

How come the electron configuration for Silver (Ag) is [Kr]4d105s1 and not [Kr] 4d9 5s2?
Mon Oct 23, 2017 11:05 pm
Forum: Trends in The Periodic Table
Topic: Cations and Anions
Replies: 2
Views: 158

### Re: Cations and Anions

this does! thank you so much!
Mon Oct 23, 2017 10:40 pm
Forum: Trends in The Periodic Table
Topic: Cations and Anions
Replies: 2
Views: 158

### Cations and Anions

I am confused about the statement: "Cations are smaller than their parent atoms, whereas anions are larger"
Cations means taking away electrons, wouldn't taking away electrons make the atoms bigger?
Anions means adding electrons, so wouldn't that make the atoms smaller?
Mon Oct 16, 2017 9:22 pm
Forum: Photoelectric Effect
Topic: Number of Photons
Replies: 4
Views: 293

### Number of Photons

What increases the number of photons? intensity?
Also, does increasing the intensity of incident light increase the number of electrons ejected? if so how? because I thought that during the experiment itself, increasing intensity did not eject an electron
Mon Oct 16, 2017 8:02 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: The negative sign
Replies: 2
Views: 245

### The negative sign

I understand the formula En= -HR/(n^2) has a negative sign, but when does our answer include a negative sign or when should it not? Also if the electron goes from (for example) n=4 to n=2, it emits energy so does that mean the energy emitted is negative some number?
Tue Oct 10, 2017 5:33 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in position [ENDORSED]
Replies: 2
Views: 546

### Re: Uncertainty in position[ENDORSED]

oops just kidding, the formula is 4 pi.
Tue Oct 10, 2017 5:27 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in position [ENDORSED]
Replies: 2
Views: 546

### Uncertainty in position[ENDORSED]

Calculate the uncertainty (indeterminacy) in position of an electron if its uncertainty in speed is one hundredth the speed of light. What I did was find p using mass of electron and .01 of speed of light then I switched around the heisenberg formula to get position variable alone delta x= h/(2pi x ...
Mon Oct 09, 2017 9:26 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spretroscopy
Replies: 1
Views: 211

### Atomic Spretroscopy

The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation? To what region of the electromagnetic spectrum does this wavelength correspond (i.e. infrared, ultraviolet, x-ray, etc.)? W...
Mon Oct 09, 2017 5:46 pm
Forum: Photoelectric Effect
Topic: Results of Photoelectric experiments
Replies: 3
Views: 292

### Results of Photoelectric experiments

To interpret the results of photoelectric experiments the model of light needs to change from a ________ model to a ________ model. What are the two missing words? would this be from a particle model to a wave model?
Mon Oct 09, 2017 12:56 am
Forum: Balancing Chemical Reactions
Topic: H.17 [ENDORSED]
Replies: 2
Views: 711

### H.17[ENDORSED]

Write a balanced equation for the complete combustion (reaction with oxygen gas) of liquid heptane, C7H16, a component typical of the hydrocarbons in gasoline, to carbon dioxide gas and water vapor.
Mon Oct 09, 2017 12:55 am
Forum: Limiting Reactant Calculations
Topic: M.15
Replies: 5
Views: 4114

### M.15

M.15 Aluminum metal reacts with chlorine gas to produce aluminum chloride. In one preparation, 255 g of aluminum is placed in a container holding 535 g of chlorine gas. After reaction ceases, it is found that 300. g of aluminum chloride has been produced. (a) Write the balanced equation for the reac...

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