Search found 50 matches
- Sun Mar 18, 2018 9:25 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Cp and Cv
- Replies: 5
- Views: 462
Cp and Cv
Is there a way to convert between the molar heat capacity at constant pressure and constant volume, Cp and Cv? Or would we have to be provided this information on an exam? Also, is there a way to convert between the specific heat capacity and the molar heat capacity?
- Sun Mar 18, 2018 9:20 am
- Forum: General Rate Laws
- Topic: Rate constant units
- Replies: 6
- Views: 649
Rate constant units
What is a general rule of thumb to figure out the units of the rate constant and the initial rate? I'm having trouble figuring them out once we get past fourth order reactions...
- Sun Mar 18, 2018 9:16 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Relation between cell potential and concentration
- Replies: 1
- Views: 237
Re: Relation between cell potential and concentration
You can use Le Chatelier's principle to help figure this out... If you decreased the concentration of one of the reactants Ecell would shift toward the reactants; if you increased the concentration of one of the reactants Ecell would shift toward the products. If you increased the concentration of o...
- Sun Mar 18, 2018 5:16 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Max work at constant T & P [ENDORSED]
- Replies: 1
- Views: 245
Max work at constant T & P [ENDORSED]
When solving for Gibbs free energy, you find the maximum work that could be done at constant pressure and temperature. Is it possible to calculate deltaG for a process at constant volume?
- Sat Mar 17, 2018 4:11 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated Systems
- Replies: 3
- Views: 333
Isolated Systems
In an isolated system, are we assuming that it is constant volume? In class, Lavelle simply defined an isolated system as one that does exchange energy or matter with the surroundings...but if we change its volume, that means we are doing work on it and therefore changing the amount of energy it con...
- Sat Mar 17, 2018 3:39 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Reaction Enthalpy
- Replies: 1
- Views: 260
Standard Reaction Enthalpy
What if you're trying to solve for the standard reaction enthalpy (using any of the three methods we learned in class), but one of the reactants or products in the reaction aren't in their most stable form? What would you have to do to solve for the standard reaction enthalpy in this case?
- Sat Mar 17, 2018 3:28 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: H+
- Replies: 3
- Views: 378
Re: H+
I'm not 100% sure either but my guess is that the solution would have to be 1M... in lecture he said that the standard state for a solution is 1M at 1atm.
- Thu Mar 15, 2018 9:22 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: PV Diagrams
- Replies: 1
- Views: 284
PV Diagrams
By looking at a PV diagram, can you distinguish between reversible and irreversible reactions? Or are PV diagrams only useful for distinguishing between isothermal, adiabatic, isobaric, and isovolumetric processes?
- Thu Mar 15, 2018 8:48 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Work in Isolated System
- Replies: 1
- Views: 404
Work in Isolated System
In class and early in chapter 8, an isolated system was defined as a system that cannot exchange energy or matter with its surroundings. However, the book defines the first law of thermodynamics as "the internal energy of an isolated system is constant." I thought you were allowed to chang...
- Thu Mar 15, 2018 8:38 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Calculating Work
- Replies: 2
- Views: 214
Re: Calculating Work
Not only is it being done against constant external pressure, but the fact that the temperature is "suddenly" increased means is it an irreversible process which indicates the use of w = -P(deltaV).
- Thu Mar 15, 2018 5:14 pm
- Forum: Phase Changes & Related Calculations
- Topic: Internal Pressure in Reversible vs Irreversible Processes
- Replies: 1
- Views: 265
Internal Pressure in Reversible vs Irreversible Processes
In an reversible process, you can basically say that external and internal pressure are changing so slow and so little that they are changing together. However, in an irreversible process, does the internal pressure have any effect on the work done? w=-Pex(deltaV) takes into consideration only exter...
- Thu Mar 15, 2018 4:59 pm
- Forum: Phase Changes & Related Calculations
- Topic: Reversible Expansions
- Replies: 3
- Views: 378
Reversible Expansions
I understand that the work a system can do is greatest in a reversible process. For example, if you look at a PV diagram you can see that the area under a curve is greatest for a reversible process. However, I am having trouble understanding it from more of a mathematical viewpoint. Can someone plea...
- Mon Feb 12, 2018 11:29 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Test 1, Question 7
- Replies: 2
- Views: 244
Re: Test 1, Question 7
The heat that is leaving the ice cube will go directly into the tea/water, so q(ice)=-q(tea). Because the ice cube is already at 0*C that means it doesn't have to cool down before it starts melting, meaning that it's going to start melting immediately. You will first want to determine if the entire ...
- Mon Feb 12, 2018 11:11 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: comparing entropies
- Replies: 1
- Views: 157
Re: comparing entropies
1. gas
2. assuming that all other parameters such as temperature are the same, then the two will have the same amount of entropy since both are considered incompressible.
3. same answer as #2.
2. assuming that all other parameters such as temperature are the same, then the two will have the same amount of entropy since both are considered incompressible.
3. same answer as #2.
- Mon Feb 12, 2018 11:05 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Laws of Thermodynamics
- Replies: 2
- Views: 291
Re: Laws of Thermodynamics
It could be an okay way of reminding yourself what each law has to do with but it doesn't necessarily define each one. The first law of thermodynamics has to do with the conservation of energy. It says that energy can neither be created nor destroyed; it is only transformed. The second law of thermo...
- Mon Feb 12, 2018 12:03 am
- Forum: Balancing Redox Reactions
- Topic: redox reactions and salts
- Replies: 2
- Views: 389
Re: redox reactions and salts
There are many redox reactions that do not result in a salt product. The use of redox reactions in electrochemistry is only one example. For example, cellular respiration and photosynthesis are redox reactions that do not result in the production of a salt. Redox reactions are reactions in which one...
- Sun Feb 11, 2018 11:58 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: heat capacity sign
- Replies: 2
- Views: 351
Re: heat capacity sign
Heat capacities can never be negative because that would mean that the substance is creating and giving off energy from thin air and this violates the first law of thermodynamics.
- Sun Feb 11, 2018 11:47 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: delta H
- Replies: 4
- Views: 262
Re: delta H
Forming a bond releases energy, thus reducing the energy of the molecule. The molecule will therefore be more stable since it is at a lower energy state.
- Sun Feb 11, 2018 11:31 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Revsersible vs. Irreversible reactions
- Replies: 3
- Views: 253
Re: Revsersible vs. Irreversible reactions
In a reversible reaction, we are assuming that it is happening so slowly that no heat is lost to the surroundings. Therefore, the total change in entropy of the universe for a reversible reaction will be equal to zero, whereas the total change in entropy of the universe for an irreversible reaction ...
- Sun Feb 11, 2018 5:10 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: avogadro's number
- Replies: 1
- Views: 148
Re: avogadro's number
To solve for W, you need to find X^N, with X being the number of possible orientations and N being the total number of molecules. You would use Avogadro's number to solve for N only if you are provided a value in grams or moles, because your goal is to find the number of molecules.
- Sun Feb 11, 2018 5:04 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: entropy and moles
- Replies: 2
- Views: 696
Re: entropy and moles
The entropy of a reaction only changes if there is a change in the number of moles of gas. This is because the number of micro states of the molecules in a solid or liquid is going to be the same regardless of how many molecules there are. However, since the molecules in a gas are moving around and ...
- Sun Feb 11, 2018 4:52 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Using q reversible
- Replies: 1
- Views: 164
Re: Using q reversible
When calculating the change in entropy of the system, you need to take heat transfer, q, into account regardless of whether it is a reversible or irreversible process. Because entropy is a state variable, the change in entropy will be the same for both reversible and irreversible processes. However,...
- Mon Feb 05, 2018 7:29 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: "Favorability"
- Replies: 5
- Views: 429
Re: "Favorability"
Favorability can be determined based on whether delta G is positive or negative; therefore, whether a reaction is spontaneous (favorable) is determined based on the changes in enthalpy and entropy values of the reaction. So you would need to look at the relative values of delta H and delta S to dete...
- Sun Feb 04, 2018 11:29 pm
- Forum: Phase Changes & Related Calculations
- Topic: Determining if reversible or irreversible
- Replies: 2
- Views: 198
Re: Determining if reversible or irreversible
One way to determine whether a reaction is reversible or irreversible is to look at the delta S. If delta S is equal to zero, the reaction is reversible (this is an ideal process). If delta S is greater than zero (all real processes), then the reaction is irreversible because heat/energy is lost to ...
- Sun Feb 04, 2018 11:24 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: requirements for reversible reactions
- Replies: 1
- Views: 97
Re: requirements for reversible reactions
Delta S would have to be zero because otherwise heat would be lost to the surroundings. If heat is lost to the surroundings, the reaction cannot be reversed. Delta G would have to be negative, indicating a release in energy. This means that the products will have lower energy than the reactants, the...
- Sun Feb 04, 2018 11:20 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Test 1 Question
- Replies: 4
- Views: 377
Re: Test 1 Question
This is an isolated system because the whole point of a cooler is to keep the contents inside cold. Therefore, no heat/energy is being exchanged between the inside and the outside. An "ideal" cooler would 100% prevent the flow of heat between the system and the surroundings.
- Mon Jan 22, 2018 2:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Concepts for Chapter 8 [ENDORSED]
- Replies: 5
- Views: 392
Re: Concepts for Chapter 8 [ENDORSED]
I would definitely recommend reading the textbook chapters we cover in class. Also doing all of the homework problems will help to solidify the concepts behind them. Hope this helps!
- Mon Jan 22, 2018 2:09 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: N: number of particle [ENDORSED]
- Replies: 4
- Views: 308
Re: N: number of particle [ENDORSED]
In the carbon monoxide example today, he put N=4 instead of N=2 because he was referring to four CO molecules, not the number of atoms within each molecule.
- Sat Jan 13, 2018 8:19 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Differences between properties
- Replies: 1
- Views: 85
Re: Differences between properties
An intensive property has to do with the element in and of itself, not the size or amount of the sample (color, temperature, solubility are examples). An extensive property is one that depends on the amount of the substance (mass and volume are examples).
- Sat Jan 13, 2018 8:15 pm
- Forum: Phase Changes & Related Calculations
- Topic: Most stable phases for halogens
- Replies: 3
- Views: 242
Re: Most stable phases for halogens
The most stable phase for any element can be looked up from the periodic table. For the halogens, fluorine will be a gas, chlorine a gas, bromine, a liquid, iodine a solid, and astatine a solid.
- Sat Dec 09, 2017 10:42 pm
- Forum: Conjugate Acids & Bases
- Topic: % Ionization [ENDORSED]
- Replies: 3
- Views: 619
Re: % Ionization [ENDORSED]
To find percent ionization, you should divide the hydrogen concentration at equilibrium by the initial concentration of the acid, and multiply by 100.
- Sat Dec 09, 2017 10:39 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Spin Quantum Number: Test 3
- Replies: 3
- Views: 342
Re: Spin Quantum Number: Test 3
There is no way of predicting whether the electron will be spin up or spin down. That is why we should always write +/- 0.5. In addition, question #8 is asking for ALL the possible values for the spin quantum number, so that would include both the positive and negative value.
- Sun Dec 03, 2017 11:15 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Do net dipole charges affect bases and acids?
- Replies: 2
- Views: 396
Re: Do net dipole charges affect bases and acids?
The greater the net dipole moment in a molecule, the stronger the acid/base, so the more it dissociates. That means that strong acids/bases have the highest electronegativity differences.
- Sun Dec 03, 2017 10:52 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Weak Acids / Strong Acids
- Replies: 5
- Views: 413
Re: Weak Acids / Strong Acids
It turns out that most acids and bases are weak, so not that many acids and bases are strong. The best way to go about it would be to memorize all of the strong acids and bases and just to assume that the others are weak.
- Sun Nov 26, 2017 11:54 pm
- Forum: Biological Examples
- Topic: Memorization of compounds
- Replies: 5
- Views: 617
Re: Memorization of compounds
I think it might be helpful to memorize the names of certain compounds; however, I think it would be a lot more helpful to have a general understanding of how to name coordination compounds.
- Sun Nov 26, 2017 11:48 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Symmetrical Molecules
- Replies: 3
- Views: 349
Re: Symmetrical Molecules
If a molecule is completely symmetrical, then it will be nonpolar. However, when it comes to 3D molecules and more complex molecules it can get a bit more tricky. Even if these molecules look symmetrical at first glance based on their shape, you have to make sure that all of the dipole moments betwe...
- Mon Nov 20, 2017 12:01 am
- Forum: Hybridization
- Topic: Hybrid orbitals
- Replies: 3
- Views: 289
Re: Hybrid orbitals
You should always fill orbitals from lowest energy to highest energy. You can use Hund's rule, the Aufbau principle, and the Pauli exclusion principle to determine the placement and spin of the electrons.
- Mon Nov 13, 2017 12:45 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Extent of memorization [ENDORSED]
- Replies: 2
- Views: 140
Re: Extent of memorization [ENDORSED]
We will definitely have to know the nomenclature for VSEPR, and I'm pretty sure we will have to know the common bond angles. We will probably have to know the angles for linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral. We won't have to know bond angles for things like trig...
- Mon Nov 13, 2017 12:40 pm
- Forum: Dipole Moments
- Topic: dipole moment arrows [ENDORSED]
- Replies: 2
- Views: 490
Re: dipole moment arrows [ENDORSED]
Yes, the arrow will always point to the most electronegative atom because the electrons are being pulled in that direction. To figure out whether a molecule is polar or non polar you need to figure out whether the dipole moments cancel. It is possible that the dipole moments will be in the same dire...
- Mon Nov 13, 2017 12:30 pm
- Forum: Sigma & Pi Bonds
- Topic: # of sigma and pi bonds [ENDORSED]
- Replies: 4
- Views: 398
Re: # of sigma and pi bonds [ENDORSED]
Yes. This is true because a bond can only have one head-on overlap. For double and triple bonds, the additional bonds will be pi bonds and will form perpendicular to the sigma bond.
- Sun Nov 05, 2017 11:28 pm
- Forum: Dipole Moments
- Topic: Dipole Moments and Electronegativity [ENDORSED]
- Replies: 2
- Views: 235
Re: Dipole Moments and Electronegativity [ENDORSED]
Yes, so the greater the difference is electronegativities of two atoms, the greater the dipole moments. Basically, the greater the electronegativity of one atom, the more likely it is to pull the electrons in the bond towards it.
- Sun Nov 05, 2017 11:03 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Shell, subshell, and orbital
- Replies: 5
- Views: 501
Re: Shell, subshell, and orbital
The principal quantum number n simply tells us what energy level the electron is found in. The angular momentum number l describes the shape of the orbital and it can range from 0 to n-1. The magnetic quantum number tells us the orientation of the orbital and ranges from -l to l.
- Sun Oct 29, 2017 11:59 pm
- Forum: Resonance Structures
- Topic: HOW [ENDORSED]
- Replies: 1
- Views: 250
Re: HOW [ENDORSED]
To determine the most stable structure you would have to determine the formal charge of each possible structure. The most stable one will be the one with the least overall formal charge.
- Sun Oct 29, 2017 11:44 pm
- Forum: Electronegativity
- Topic: Electronegativity [ENDORSED]
- Replies: 3
- Views: 378
Re: Electronegativity [ENDORSED]
Another way to think about it is as you move to the right of the periodic table you are adding more positive charge to the nucleus but the electrons are being added to the same orbital; therefore, the electrons are attracted more strongly to the nucleus. As you move down a period, even though you ar...
- Tue Oct 24, 2017 10:29 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: 3d and 4s
- Replies: 5
- Views: 532
Re: 3d and 4s
Generally, the 4s orbital will be filled before the 3d orbital, because 4s is of lower energy than 3d. If you follow the fourth period of the periodic table from left to right, you see that 4s gets filled before 3d. However, two exceptions to this in the fourth period are chromium and copper: these ...
- Tue Oct 24, 2017 9:32 am
- Forum: Ionic & Covalent Bonds
- Topic: Ionization Energy [ENDORSED]
- Replies: 5
- Views: 461
Re: Ionization Energy [ENDORSED]
Yes, ionization energy is the energy required to remove an electron from an atom. Ionization energies differ for each element, generally increasing across a period and decreasing down a group. The ionization energy for an element will always be the same if, for example, it is the first electron you ...
- Sun Oct 15, 2017 10:59 am
- Forum: DeBroglie Equation
- Topic: Units for Mass [ENDORSED]
- Replies: 3
- Views: 282
Re: Units for Mass [ENDORSED]
From my experience, you will almost always use kilograms when plugging numbers into equations. But to be 100% sure, you should make sure to look at the units for any constants you're using in your calculations and at the units of other values you are plugging in. Make sure that these units cancel ou...
- Sun Oct 15, 2017 10:35 am
- Forum: Properties of Electrons
- Topic: Speed/Energy of Electrons
- Replies: 4
- Views: 396
Re: Speed/Energy of Electrons
I think I'm also kind of confused between speed and frequency. If light has a higher frequency doesn't that mean that it's going to be faster?
- Sun Oct 08, 2017 3:36 pm
- Forum: Limiting Reactant Calculations
- Topic: Calculating how much of the excess remains [ENDORSED]
- Replies: 4
- Views: 408
Re: Calculating how much of the excess remains [ENDORSED]
Wouldn't you see how much of the excess product is consumed by comparing the molar ratios of the two (or more) reactants? You can never compare the masses of two different reactants; you would have to use moles, right?
- Sun Oct 08, 2017 3:11 pm
- Forum: Significant Figures
- Topic: Sig Fig in final answer [ENDORSED]
- Replies: 3
- Views: 736
Re: Sig Fig in final answer [ENDORSED]
Your final answer in this case would only have two significant figures. This is because your final answer can only be as precise as the least precise value you used in your calculations.