## Search found 55 matches

Fri Mar 16, 2018 4:40 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8046
Views: 1412649

### Re: Post All Chemistry Jokes Here

What do you call iron particles blowing away in the wind?
Febreeze
Fri Mar 16, 2018 4:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining
Replies: 7
Views: 422

### Rate Determining

How do you determine whether a step in a mechanism is slow or fast if they don't already give it to you?
Fri Mar 16, 2018 2:56 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8046
Views: 1412649

### Re: Post All Chemistry Jokes Here

What kind of fish is made out of 2 sodium atoms? 2 Na
Fri Mar 16, 2018 2:54 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8046
Views: 1412649

### Re: Post All Chemistry Jokes Here

What is the show cesium and iodine love watching together? CSI
Fri Mar 16, 2018 2:46 am
Forum: Second Order Reactions
Topic: 3rd order?
Replies: 7
Views: 739

### Re: 3rd order?

If you look at first order and second order reactions, when you increase the order, you raise the power of the L and the mol in the units. Thus as you increase the order further, the power continues to rise.
Fri Mar 16, 2018 2:43 am
Forum: First Order Reactions
Topic: Determining Reaction Order
Replies: 5
Views: 442

### Re: Determining Reaction Order

The reaction order is found experimentally, and is usually stated in the question itself. For zero order, rate = k; for first order, the rate is k*[A]; and for second order, the rate is k*[A]^2
Fri Mar 16, 2018 2:39 am
Forum: Zero Order Reactions
Topic: zero order rate?
Replies: 14
Views: 820

### Re: zero order rate?

Yup! Zero order rates are independent of concentration, but assumes that there is some reactant.
Fri Mar 16, 2018 2:23 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.51
Replies: 1
Views: 130

### 15.51

How do you determine which of the steps is the rate-controlling step? Is it just the slower one/Why?
Fri Mar 16, 2018 2:19 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.65 part b
Replies: 1
Views: 121

### Re: 15.65 part b

The reverse reaction has a lower activation barrier than the forward reaction, so the forward reaction is endothermic
Fri Mar 16, 2018 2:13 am
Forum: Phase Changes & Related Calculations
Topic: 8.23
Replies: 5
Views: 478

### Re: 8.23

I don't think you factor in mass when you calculate the heat capacity of the calorimeter
Fri Mar 16, 2018 1:58 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond/Graphite
Replies: 4
Views: 1698

### Re: Diamond/Graphite

Diamond is thermodynamically unstable because delta G for diamond to graphite is negative and therefore spontaneous, but the transition from diamond to graphite has a large activation energy barrier, so diamond is not likely to transition on its own to graphite and is therefore kinetically stable.
Fri Mar 16, 2018 1:44 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm Question
Replies: 2
Views: 328

### Re: Midterm Question

You use specific heat capacity because they state that all the masses of the pots are the same. lf you were to compare molar heat capacity, you would have to calculate moles and then standardize it/divide by the lowest to have a comparable scale. It's easier to compare by specific heat capacity beca...
Fri Mar 16, 2018 1:33 am
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 4
Views: 338

### Re: Midterm 4a

If it helps, draw the two diagrams of reversible and irreversible reaction. Since there is no change in pressure (they don't give you a second value), then you don't have to integrate to find work, and you can just use w = -P * delta V
Fri Mar 16, 2018 1:28 am
Forum: Calculating Work of Expansion
Topic: Midterm Q3B
Replies: 7
Views: 525

### Re: Midterm Q3B

If the pots are of the same weight, you must compare the specific heat capacities (mass is not a factor if they are all the same weight). The specific heats of iron, copper, and aluminum are 0.4495 J*C*(g^-1), 0.3846 J*C*(g^-1), and 0.9025 J*C*(g^-1) respectively. Since copper has the lowest specifi...
Fri Mar 16, 2018 1:22 am
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 5
Views: 473

### Re: Midterm 4a

Because they don't give you a different pressure value, you can assume that external pressure is constant. In the case of constant external pressure, the expansion is irreversible
Fri Mar 16, 2018 1:18 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Temperature in Entropy Change for Monoatomic Ideal Gas Midterm Question 6B
Replies: 2
Views: 306

### Re: Temperature in Entropy Change for Monoatomic Ideal Gas Midterm Question 6B

When you calculate n, you know the information before the temperature change. Since the rest of the variables (in a more general example) can change during a temperature change, you should calculate n at the state in which the only unknown is n, which in this case, is when T = 303 K
Fri Mar 16, 2018 1:16 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: residual entropy
Replies: 2
Views: 461

### Re: residual entropy

Residual entropy is the entropy of a sample at T=0, due to positional disorder at that temperature. If it were to be on the final, I would think something along the lines of the book example, where we are asked to confirm whether or not the molecules in the crystal form are arranged randomly or not,...
Fri Mar 16, 2018 1:11 am
Forum: Van't Hoff Equation
Topic: Confusion on different versions of the Van't Hoff equation?
Replies: 4
Views: 545

### Re: Confusion on different versions of the Van't Hoff equation?

Both equations will give you the same answer, and you can derive the equation we use from the one in the book. We use the one that we do because it's simpler, so you should be fine using the one Lavelle taught us
Fri Mar 16, 2018 1:06 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculating Gibbs Free Energy
Replies: 4
Views: 377

### Re: Calculating Gibbs Free Energy

Use difference of sums when the information given pertains to the Gibbs free energy of products or reactants, and the other equation when given entropy and enthalpy. Determine what information the question gives you and then you can choose an equation to plug into accordingly
Fri Mar 16, 2018 1:02 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: enthalpy of sublimation
Replies: 5
Views: 493

### Re: enthalpy of sublimation

As long as you know the equation, delta Hsub = Hvapor - Hsolid, or delta Hsub = delta Hfus + delta Hvap, you should be fine. Just remember that sublimation is changing two states, rather than just one phase transition. Since enthalpy is a state function, you can just add the enthalpy of each phase t...
Fri Mar 16, 2018 12:52 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: concept question
Replies: 2
Views: 289

### Re: concept question

Because entropies are a measure of disorder, gases have higher entropies than liquids. Thus, changes in temperature are more reflected in the entropy change of gases than of liquids.
Fri Mar 16, 2018 12:44 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G at Boiling Point
Replies: 3
Views: 2059

### Re: Delta G at Boiling Point

If you remember the graph of phase transitions, as a phase transition is about to occur, energy is still supplied to the system but temperature doesn't change immediately. Thus, at the point of a phase transition, such as the boiling point, there is no change in temperature. As delta G is a factor o...
Fri Mar 16, 2018 12:41 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp or Cv in temperature change
Replies: 3
Views: 494

### Re: Cp or Cv in temperature change

Based on what information is given, you can tell which variable is staying constant and then accordingly use either Cp or Cv
Fri Mar 16, 2018 12:35 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Celsius to Kelvin Clarification
Replies: 3
Views: 350

### Re: Celsius to Kelvin Clarification

The equation sheet says K = C + 273.15, so I would just use that to be safe. You can always adjust decimal points based on the number of sig figs in the answer. I typically use 273.15 and I've never been docked for the potential discrepancies
Fri Mar 16, 2018 12:30 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm Question
Replies: 4
Views: 352

### Re: Midterm Question

Because you are calculating a change in temperature, a change in celsius is the same as a change in kelvin. Be sure to convert the units if you aren't doing a change in temp calculation, because most of the constants deal with Kelvin, or if the question specifically asks you to report temperature in...
Fri Mar 16, 2018 12:02 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Example 8.5
Replies: 3
Views: 298

### Re: Example 8.5

Even as an ideal gas expands isothermally, its molecules continue to move at the same speed, so the kinetic energy doesn't change. Also the total potential energy of these molecules is the same because there aren't any intramolecular forces. Since neither the total kinetic energy nor the total poten...
Thu Mar 15, 2018 11:54 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: delta s surrounding and system
Replies: 3
Views: 1622

### Re: delta s surrounding and system

The signs of the system and surrounding are opposite to one another usually when one loses and the other gains heat. For example, if the surroundings are losing heat, the system will gain heat, making delta Ssurr negative and delta Ssys positive.
Wed Feb 07, 2018 11:47 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Degeneracy vs Disorder
Replies: 4
Views: 295

### Re: Degeneracy vs Disorder

Disorder refers to the way that energy and matter tend to disperse. Degeneracy refers to the number of ways of achieving a given state. Degeneracy occurs if the energy is unable to stay in one state, represented by the W value. For example, the different microstates, which correspond to each arrange...
Wed Feb 07, 2018 11:34 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.99 math
Replies: 2
Views: 213

### Re: 8.99 math

The reason that 0.130 mol Zinc is relevant is because the enthalpy of formation is kJ per mole. Therefore, when you find the energy of the reaction, you have to find the amount of energy used to carry the reaction to completion with 0.130 mol of Zinc. The 800 grams comes from the volume of the HCl, ...
Wed Feb 07, 2018 11:19 am
Forum: Phase Changes & Related Calculations
Topic: Differential Thermal Analysis
Replies: 2
Views: 171

### Re: Differential Thermal Analysis

The outline for the chapter explicitly includes Box 8.2, but doesn't mention 8.1, so I assume we don't need to. As far as heating curves are concerned, I think you should focus on the steepness of the slope (more steep = lower heat capacity) and the flat lines that appear during phase changes becaus...
Wed Feb 07, 2018 11:13 am
Forum: Phase Changes & Related Calculations
Topic: Phase change
Replies: 4
Views: 251

### Re: Phase change

You can usually tell it's a phase change from the question either explicitly stating it or from the information given. I think these questions are usually about water, because we already know the melting/freezing point. In the case of #7, since you have a cube of ice at 0.0 Celsius, which is the fre...
Wed Feb 07, 2018 11:01 am
Forum: Phase Changes & Related Calculations
Topic: Units for Internal Energy
Replies: 5
Views: 324

### Re: Units for Internal Energy

I think you can use either in your answers, but try and maintain the one in which information was given in the question. Typically, one is also more favorable in terms of sig figs, but either should be fine
Thu Jan 25, 2018 6:57 pm
Forum: Phase Changes & Related Calculations
Topic: Carbon as graphite [ENDORSED]
Replies: 7
Views: 484

### Re: Carbon as graphite[ENDORSED]

Because you are finding the standard enthalpy, you have to use the elements in their most stable state. For hydrogen and oxygen, the most stable form is in H2 and O2 gas, but for carbon, the most stable state is as graphite.
Thu Jan 25, 2018 6:47 pm
Forum: Phase Changes & Related Calculations
Topic: Homework Help on 8.67
Replies: 2
Views: 211

### Re: Homework Help on 8.67

Another way to think of it is thinking of deriving the enthalpy of formation of gas. To do so, we would add (enthalpy of formation of liquid) + (enthalpy of vaporization) = (enthalpy of formation of gas). Therefore, to find the enthalpy of formation of liquid, you would have to subtract: (enthalpy o...
Thu Jan 25, 2018 6:44 pm
Forum: Phase Changes & Related Calculations
Topic: Self Test 8.7A
Replies: 2
Views: 136

### Re: Self Test 8.7A

The formula for deltaH is deltaU + P*deltaV or work + heat + P*deltaV. At constant pressure, pressure internal and pressure external are the same so work (aka -Pex*deltaV) = P*deltaV. Thus the two values cancel out, and deltaH = heat
Tue Dec 05, 2017 3:02 am
Forum: Bronsted Acids & Bases
Topic: Bronsted vs. Lewis
Replies: 4
Views: 327

### Re: Bronsted vs. Lewis

A Lewis acid id more broadly defined, because while the compound may be able to give accept electrons, it may not have a proton to give. For example, when carbon dioxide reacts with water, the CO2 is the Lewis acid, as it accepts an electron pair from the oxygen of H20. However, CO2 is not a Bronste...
Mon Dec 04, 2017 2:32 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Question 11.89 Part A
Replies: 2
Views: 211

### Re: Question 11.89 Part A

In my solutions book it said 2A forms B + 2C. When I got this answer, it was because of the way I did my ice box. If A starts at ~27 and B and C start at 0, you look at their final partial pressures to find the change A B C i 27 0 0 c -x e 17 5 10 so if you calculate -x to be 10, then the change in ...
Mon Dec 04, 2017 12:47 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ICE table question
Replies: 5
Views: 4690

### Re: ICE table question

When you consider the change in x, you have to think of the way that the quantities are changing in the reaction. Typically you choose one of the compounds in the reaction (based on the known information) to change. For example, if you decrease one of the reactants, all the reactants should decrease...
Mon Dec 04, 2017 12:44 am
Forum: Biological Examples
Topic: Ligands [ENDORSED]
Replies: 3
Views: 438

### Re: Ligands[ENDORSED]

I think it's a good idea to memorize the ligands and their charges, because if you are asked you to find the oxidation number of the transition metal as we were sometimes asked in the homework problems, you need to know the charges of the ligands so that you can find the oxidation number that would ...
Mon Dec 04, 2017 12:41 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Order of ligands [ENDORSED]
Replies: 2
Views: 226

### Re: Order of ligands[ENDORSED]

When you write out the name, the ligands must be in alphabetical order, and in the book, it says that the chemical formula must be in alphabetical order as well. This is why even if the ligands are diaquachloro..... (for example) when writing the formula, you would write Cl(OH2)2
Mon Dec 04, 2017 12:32 am
Forum: Hybridization
Topic: 4.43
Replies: 2
Views: 287

### Re: 4.43

The s-character can be thought of as the percent of s out of all the orbitals. For example, an sp hybridized atom has 50% s-character, a sp^2 hybridized atom has 33.3% s-character, a sp^3 hybridized atom has 25% s-character, and so on. Based on the question, as s-character increases, the bond angle ...
Tue Nov 14, 2017 1:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: CO2 vs. H2O
Replies: 6
Views: 1847

### Re: CO2 vs. H2O

In CO2, both oxygens are more electronegative than the carbon, but they pull equally apart from one another, so there is no dipole moment (the pulls cancel). Meanwhile, in H2O, oxygen has two lone pairs as well as the bonds to the hydrogen, so the electrons are concentrated on oxygen and are not can...
Tue Nov 14, 2017 1:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Memorization
Replies: 5
Views: 394

### Re: Memorization

I would say try and learn basic shapes and their names and angles. In my discussion, my TA went through 5 shapes (linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral) and from each of those, changed bonds into lone pairs until there were only three atoms (two bonds) left. This...
Tue Nov 14, 2017 1:15 pm
Forum: Dipole Moments
Topic: Dipole Moment of CO
Replies: 3
Views: 1443

### Re: Dipole Moment of CO

The shape doesn't necessarily affect whether or not there exists a dipole moment or not. Instead, look at the formal charges or the electronegativity of the atoms. Although oxygen is more electronegative, the bonding and formal charge in the case of CO breaks the rule. Carbon is slightly negative be...
Tue Nov 14, 2017 1:06 pm
Forum: Octet Exceptions
Replies: 4
Views: 1307

Radicals go on the most electronegative atom. Biradicals are merely molecules with two radicals or two instances of unpaired electrons. I think these are noticeable when you are doing a Lewis structure and you calculate the formal charge of the atoms, but I'm pretty sure we won't be asked for the Le...
Tue Nov 14, 2017 1:03 pm
Forum: Electronegativity
Topic: Trends in periodic table
Replies: 6
Views: 835

### Re: Trends in periodic table

A lot of times they ask you to compare trends such as electronegativity, electron affinity, and ionization energy between elements and they include noble gases but in these cases, noble gases are the least electronegative, have the highest ionization energy, and the lowest electron affinity because ...
Tue Nov 14, 2017 12:54 pm
Forum: Trends in The Periodic Table
Topic: s-block vs p-block
Replies: 5
Views: 1181

### Re: s-block vs p-block

The p-block is actually mostly non-metals. Elements in the s-block have much lower ionization energies, so they give away electrons easily whereas the p-block elements have more filled shells, and are closer to having a full shell, so they are less likely to give away electrons as easily. Additional...
Tue Nov 14, 2017 12:49 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Order of Orbitals
Replies: 10
Views: 850

### Re: Order of Orbitals

If you're wondering about the order in respect to the d orbital, once you reach Ar the next electron goes into the 4s subshell because it has a lower energy than the 3d subshell. However, once the 3d subshell starts filling (element 21) it drops in energy level, which is why it is written first, and...
Tue Nov 14, 2017 12:46 pm
Forum: DeBroglie Equation
Topic: Help with the concept of De Broglie's
Replies: 8
Views: 516

### Re: Help with the concept of De Broglie's

The wavelength exists, but is merely not detectable. Typically, if the wavelength is smaller than 1*10^-12 m (the size of gamma rays) then its not detectable. DeBroglie's suggests that all matter has wavelike properties, only that some are not detectable or visible (typically, objects with larger ma...
Fri Nov 03, 2017 11:49 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Subshells
Replies: 3
Views: 315

### Re: Subshells

Theoretically, it's possible for l to be higher than 3 (you could potentially have a g orbital in which case the first occurance would be in 5g) but we don't directly address it in this class, so you only need to know up to f orbitals, and that for an f orbital, l = 3
Tue Oct 17, 2017 6:58 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation! [ENDORSED]
Replies: 8
Views: 914

### Re: Rydberg Equation![ENDORSED]

If you use the formula as given on the sheet E = (-hR)/n^2, you should be able to do Delta E = Efinal - Einitial without any issues with negative signs. If you're solving backwards for an n value, you can still use this equation. You can rewrite Delta E = Efinal - Einitial as Delta E = (-hr)/n^2 - (...
Tue Oct 17, 2017 6:54 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Formula
Replies: 2
Views: 221

### Re: Rydberg Formula

If you look online, the Rydberg constant given might actually vary, so the equation itself might be different. My TA said to do Rydberg equations the long way, however, so using the formula En = (-hR)/n^2 for each energy level, and then finding the change in E between the levels. This will give you ...
Tue Oct 17, 2017 6:49 pm
Forum: Photoelectric Effect
Topic: Post Module #23 [ENDORSED]
Replies: 2
Views: 215

### Re: Post Module #23[ENDORSED]

The result of the photoelectric experiment showed that increasing the intensity of the light did not eject electrons if the initial light did not eject electrons, dismissing the idea that light was acting as a wave (in which case increasing intensity would increase amplitude and eject electrons). It...
Thu Oct 05, 2017 1:39 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Fundamentals E.35
Replies: 2
Views: 570

### Re: Fundamentals E.35

in the solutions the manual, they actually did (final-initial)/final: I believe it was to show the percent of the final fluorapetite that is caused by the conversion? i'm not entirely sure but that's how i rationalized the solution manual
Thu Oct 05, 2017 1:26 pm
Forum: Limiting Reactant Calculations
Topic: What is the mass of AgCl produced?
Replies: 10
Views: 4384

### Re: What is the mass of AgCl produced?

After you calculate the moles of each, compare the moles of C6H9Cl3 and moles of AgNO3. Since the balanced equation has a 1:3 ratio, the number of moles of AgNO3 should be at least three times more than the number of moles of C6H9Cl3. If there are less than 3x, then AgNO3 is the limiting reactant be...