Search found 66 matches

Wed Feb 05, 2020 7:24 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Spontaneous
Replies: 4
Views: 58

Re: Spontaneous

For a simpler example, ice melting to water at room temperature is favorable (low enthalpy high entropy), but water freezing into ice is not.
Wed Feb 05, 2020 7:22 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Temperature effect on Entropy
Replies: 1
Views: 41

Re: Temperature effect on Entropy

This confused me too, but the thing to remember is that the equation is solving for the change in entropy, not entropy itself, and the temperature in the equation is a constant, not change in temperature. If a system is already at high temperature and the molecules are excited, it's change is entrop...
Wed Feb 05, 2020 6:49 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: ∆U When ∆T = 0
Replies: 5
Views: 112

Re: ∆U When ∆T = 0

Temperature is a number directly proportional to the energy of a system (at least when you're working with ideal gasses, which we are). So when there is no change in T, there also cannot be any change in U.
Wed Feb 05, 2020 6:40 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: closed vs isolated
Replies: 14
Views: 119

Re: closed vs isolated

A closed system can exchange energy with its environment, but an isolated system cannot.
Wed Feb 05, 2020 6:37 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Topics on the Midterm
Replies: 22
Views: 271

Re: Topics on the Midterm

Everything on outlines 1-4 will be covered.
Wed Feb 05, 2020 6:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reversible vs Irreversible
Replies: 4
Views: 31

Re: Reversible vs Irreversible

In lecture today we learned that most biochemical reactions are very irreversible and that few reactions are truly reversible, but we assume that they are when we want to solve for the maximum entropy.
Wed Feb 05, 2020 6:33 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb calorimetry
Replies: 2
Views: 22

Re: Bomb calorimetry

A normal calorimeter is an open system, while a bomb calorimeter is a closed system, so you can assume volume is constant
Wed Feb 05, 2020 6:31 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cp and Cv
Replies: 10
Views: 77

Re: Cp and Cv

If we need to use these values they will be provided to us on the test.
Wed Feb 05, 2020 6:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: C = K?
Replies: 5
Views: 86

Re: C = K?

If the temperature raises from 25 to 27 C, by converting to K it is being raised from 298 to 300 K. However, the change in temperature for both is still 2. Therefore doesn't matter if you use kelvin or Celcius to measure delta T (unless you need to cancel out units later in the problem).
Wed Feb 05, 2020 6:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: standard reaction enthalpy
Replies: 3
Views: 13

Re: standard reaction enthalpy

Both are acceptable, however Standard Enthalpy of Formation is required to be in kJ/mol.
Wed Feb 05, 2020 6:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: assuming temperature
Replies: 2
Views: 29

Re: assuming temperature

If delta H is noted to be at STP, then you can assume it is at 25 degrees C. If not, the temperature should be stated
Sun Jan 19, 2020 10:01 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Replies: 8
Views: 79

Typically when you are solving for x from an ICE table and x is not less than 10^-3, it will be easiest to solve with the quadratic formula
Sun Jan 19, 2020 9:59 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q < K
Replies: 16
Views: 133

Re: Q < K

Yes, when a reaction proceeds to the right, it forms products
Sun Jan 19, 2020 9:57 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: temperature
Replies: 10
Views: 83

Re: temperature

Every K value correlates to a temperature. When you are given a table of k values, make sure you pick the one that correlates to the temperature you are given
Sun Jan 19, 2020 9:56 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ICE Tables
Replies: 13
Views: 97

Re: ICE Tables

H2O is in excess, so the change in concentration is negligible
Sun Jan 19, 2020 9:54 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: X was ignored
Replies: 27
Views: 208

Re: X was ignored

1.8x10^-5 expanded is the same thing as .000018. .1-.000018 = .09999 something, which is very very close to .1. So when x is very small, it will not affect the constant in any significant way
Sun Jan 12, 2020 12:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Temperature and K
Replies: 6
Views: 75

Re: Temperature and K

This is why every time we are given a K value we are also given a temperature at which the reaction took place. At different temperatures, the K value will be different.
Sun Jan 12, 2020 12:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: when to use Kc vs Kp
Replies: 11
Views: 77

Re: when to use Kc vs Kp

The brackets are strictly used to show that we are dealing with molar concentrations, and are used to solve for kc. Parenthesis and kp are used to deal with pressure
Sun Jan 12, 2020 12:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q<K
Replies: 4
Views: 25

Re: Q<K

When a reaction reaches equilibrium, no matter how many products or reactants you start with, you will always have the same ratio of products to reactants, K. So if you were to take a sample of the reaction before it reached equilibrium, measure the concentrations of reactants and products, and foun...
Sun Jan 12, 2020 12:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Le Chatelier's Principle
Replies: 5
Views: 38

Re: Le Chatelier's Principle

No, because they are pure substances and therefore don't have concentrations to use in the ratio
Sun Jan 12, 2020 12:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: meaning of equilibrium [ENDORSED]
Replies: 3
Views: 33

Re: meaning of equilibrium[ENDORSED]

Chemical equilibrium means that the net change of the forwards and reverse reactions cancel out, so there is a constant, k, that expresses the ratio of the products and the reactants at equilibrium. This doesn't mean they have equal concentrations (it's very rare for k to be 1), but it does mean tha...
Sun Dec 01, 2019 8:14 pm
Forum: Lewis Acids & Bases
Topic: Lewis vs Bronsted
Replies: 4
Views: 46

Re: Lewis vs Bronsted

I believe yes, because not all acids and bases lose or accept protons.
Sun Dec 01, 2019 8:10 pm
Forum: Lewis Acids & Bases
Topic: Proton acceptor and proton donor?
Replies: 33
Views: 397

Re: Proton acceptor and proton donor?

Acids donate protons, bases accept them
Sun Dec 01, 2019 8:09 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH calcuations
Replies: 8
Views: 99

Re: pH calcuations

So far, yes
Sun Dec 01, 2019 8:06 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Ligand
Replies: 4
Views: 40

Re: Ligand

A chelate is a ring structure of ligands around a central metal ion
Sun Dec 01, 2019 8:04 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Weak vs. Strong Acids
Replies: 3
Views: 32

Re: Weak vs. Strong Acids

An acid or base must dissociate completely to be strong. Otherwise, it is weak
Sun Nov 24, 2019 11:44 pm
Forum: Lewis Acids & Bases
Topic: Lewis acids + bases and Bronsted acids + bases
Replies: 6
Views: 94

Re: Lewis acids + bases and Bronsted acids + bases

A lewis acid/base accepts/donates electron pairs, while a bronsted acid/base donates/accepts protons
Sun Nov 24, 2019 11:42 pm
Forum: Lewis Acids & Bases
Topic: Why is it that e- rich species will replace H2O ligands?
Replies: 1
Views: 36

Re: Why is it that e- rich species will replace H2O ligands?

The bonds they would form are stronger than the ones the H2O are forming, so they force the H2O out of the way
Sun Nov 24, 2019 11:40 pm
Forum: Lewis Acids & Bases
Topic: Donor and Acceptor
Replies: 6
Views: 63

Re: Donor and Acceptor

It confused me too, I tend to remember it by thinking that bases usually go from a relatively negative charge to a relatively positive one (by donating a lone pair or accepting a proton) and acids do the opposite
Sun Nov 24, 2019 11:37 pm
Forum: Lewis Acids & Bases
Topic: Hydronium ion
Replies: 5
Views: 61

Re: Hydronium ion

When an acid is dissolved in water, the hydrogen will dissociate and bond with a water molecule, forming H3O
Sun Nov 24, 2019 11:36 pm
Forum: Lewis Acids & Bases
Topic: When does a complex become a chelate?
Replies: 3
Views: 74

Re: When does a complex become a chelate?

A chelate is a complex containing at least one ligand that forms a ring of atoms that includes the central atom.
Sun Nov 24, 2019 11:30 pm
Forum: Lewis Acids & Bases
Topic: When does a complex become a chelate?
Replies: 3
Views: 74

Re: When does a complex become a chelate?

A chelate is a complex containing at least one ligand that forms a ring of atoms that includes the central atom.
Sun Nov 17, 2019 11:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Understanding longer molecule VSPER shapes.
Replies: 3
Views: 45

Re: Understanding longer molecule VSPER shapes.

When the molecule is a long chain, you determine the shape of each portion of the chain around each central molecule separately
Sun Nov 17, 2019 11:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming the Molecular Shapes
Replies: 7
Views: 123

Re: Naming the Molecular Shapes

The names are mostly pretty intuitive, it's usually most helpful to envision the molecule in a three-dimensional space. I also use flashcards for some of the harder ones like seesaw.
Sun Nov 17, 2019 11:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Instantaneous Dipole versus Induced Dipole
Replies: 4
Views: 74

Re: Instantaneous Dipole versus Induced Dipole

Instantaneous dipoles are momentary moments where one side of the molecule will be more electronegative than the other as electrons move around the nuclei. When two nonpolar molecules are next to each other, these instantaneous dipoles form induced dipoles, as the temporarily negative side of one is...
Fri Nov 15, 2019 3:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: varying VSEPRs
Replies: 7
Views: 109

Re: varying VSEPRs

No, the shape doesn't vary
Fri Nov 15, 2019 3:56 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 6
Views: 77

Re: Bond Angles

If you can remember what the shape looks like three-dimensionally, most of the angles (except 109.5) are pretty intuitive. For example, for the trigonal bipyramidal shape in a 3d space, you can see visually where the 90 and 180-degree angles are.
Mon Nov 11, 2019 5:21 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: forces and boiling points
Replies: 6
Views: 54

Re: forces and boiling points

Another important thing to remember is that CH4 does not form hydrogen bonds because C is not electronegative enough. It follows the normal dispersion rules, and Cl has more electrons than H
Mon Nov 11, 2019 5:17 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: melting points
Replies: 6
Views: 56

Re: melting points

Another way to think about it is that O is more electronegative than S, so its dipole moments are more dramatic than H2S's. The positive and negative ends form stronger bonds because of it.
Mon Nov 11, 2019 5:14 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: The Strength of Hydrogen Bonding
Replies: 4
Views: 41

Re: The Strength of Hydrogen Bonding

since F, O, and N are the three most electronegative elements, and H is very positive, hydrogen bonds are very strong and hard to break apart
Mon Nov 11, 2019 5:11 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: types of intermolecular forces
Replies: 5
Views: 41

Re: types of intermolecular forces

You can tell if a molecule is polar if one side is more electronegative than the other. I like to think of dipole-dipole bonds like magnets; if two things with positive and negative sides are close together, the positive will bind with the negative.
Mon Nov 04, 2019 1:35 am
Forum: Resonance Structures
Topic: Resonance Structure
Replies: 2
Views: 62

Re: Resonance Structure

When you have a Lewis dot structure where a double bond could be placed with a different atom of the same element and the formal charges would not change, you draw the structure each way it is possible for it to form and draw arrows between the structures, showing that they are interchangeable
Mon Nov 04, 2019 1:31 am
Forum: Dipole Moments
Topic: Dipole Arrow
Replies: 5
Views: 48

Re: Dipole Arrow

The arrow point should point towards the negative dipole, the + should point towards the positive.
Mon Nov 04, 2019 1:30 am
Forum: Octet Exceptions
Replies: 4
Views: 56

There is a biological theory of aging that revolves around free radicals. Basically, it’s thought that as the radicals bind to parts of the cell they wear it down over time, especially DNA.
Mon Nov 04, 2019 1:28 am
Forum: Octet Exceptions
Topic: Lewis Acids and Bases?
Replies: 11
Views: 150

Re: Lewis Acids and Bases?

A Lewis acid is a lone pair acceptor, and a Lewis pair is a lone pair donor. I believe they are similar to covalent bonds, except they typically form as separate molecules and join to fulfill their individual needs
Mon Nov 04, 2019 1:25 am
Forum: Dipole Moments
Topic: Polar Covalent Bonds
Replies: 2
Views: 33

Re: Polar Covalent Bonds

Some elements are more electronegative than others; for example, Fluorine has more protons in its nucleus than Carbon, so it will pull on electrons in a covalent bond more strongly.
Sun Oct 27, 2019 9:58 am
Forum: Ionic & Covalent Bonds
Topic: How are lewis structures filled?
Replies: 6
Views: 60

Re: How are lewis structures filled?

I typically give each atom around the center an octet first and adjust from there with double bonds and single pairs in the center, but I think both ways work
Sun Oct 27, 2019 9:54 am
Forum: Ionic & Covalent Bonds
Topic: Double bond placement
Replies: 15
Views: 181

Re: Double bond placement

In general, hydrogen likes to have one bond, oxygen likes two, nitrogen likes three, and carbon likes four. When you decide where to put double bonds or triple bonds, arrange them so that the most atoms have 0 formal charge and all the electrons are used, which usually follows the rules above.
Sun Oct 27, 2019 9:51 am
Forum: Ionic & Covalent Bonds
Topic: Explaining periodic trends
Replies: 3
Views: 45

Re: Explaining periodic trends

I think it depends on the element but in general, I think I remember size and shielding being more influential on atomic radius than electrostatic interactions between the protons and the nucleus. However, both are important to consider, and I don't think there were any questions in the homework whe...
Sun Oct 27, 2019 9:45 am
Forum: Resonance Structures
Topic: Bond lengths
Replies: 5
Views: 49

Re: Bond lengths

I believe he said in our lecture on Friday that we don't need to know how to find the bond lengths in this class, just that double bonds are shorter than single bonds between the same two elements, and bonds in resonant structures are between those two lengths.
Sun Oct 27, 2019 9:43 am
Forum: Lewis Structures
Topic: Drawing Lewis Structure
Replies: 6
Views: 47

Re: Drawing Lewis Structure

I believe in this class you have to draw them in order to ensure that each atom gets the right number of electrons in the structure
Sun Oct 20, 2019 2:08 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Overlapping
Replies: 4
Views: 64

Re: Overlapping

Yes, they do overlap, especially in electrons with more shells further from the nucleus. Like the last responder said, the probability isn't necessarily doubled, but it is influenced by the extra shell
Sun Oct 20, 2019 2:06 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Inner e- and Outer e-
Replies: 14
Views: 134

Re: Inner e- and Outer e-

Inner electrons feel more electrostatic attraction from the positively charged nucleus. This charge is stronger the further down the periodic table you go, so the inner electrons in those atoms are closer to the nucleus. Outer electrons are shielded from this pull by the inner electrons, so they are...
Sun Oct 20, 2019 2:04 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Planes
Replies: 6
Views: 45

Re: Nodal Planes

Nodal planes are planes in the p, d, and f orbitals with zero electron density probability. In other words, there is no likelihood of finding an electron in that spot.
Sun Oct 20, 2019 2:00 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Hund's rule and Pauli Exclusion Principle
Replies: 14
Views: 224

Re: Hund's rule and Pauli Exclusion Principle

You use Hund's rule and the Pauli Exclusion Principle together to write the ground-state electron configuration of an atom. Hund's rule tells you to fill in orbitals with one electron each with parallel spin before doubling up, and the Pauli Exclusion Principle tells you to give the paired electrons...
Sun Oct 20, 2019 1:56 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Structure of electrons
Replies: 5
Views: 56

Re: Structure of electrons

An orbital has three quantum numbers, while a shell is only defined by n
Thu Oct 10, 2019 2:14 pm
Forum: Einstein Equation
Topic: Numbers to memorize [ENDORSED]
Replies: 37
Views: 1760

Re: Numbers to memorize[ENDORSED]

It's nice to have them memorized because they are used often, but they will be given to us on tests
Thu Oct 10, 2019 2:12 pm
Topic: Black Body
Replies: 4
Views: 2174

Re: Black Body

Black bodies are an idealization; an actual black body that emits and absorbs all frequencies does not exist. Stars are approximately like black bodies, but not exactly
Thu Oct 10, 2019 2:08 pm
Forum: Properties of Light
Topic: Minimum Frequency
Replies: 2
Views: 61

Re: Minimum Frequency

If an electron is removed with zero kinetic energy or the energy of the light is the same as the energy required to remove an electron, you can use the energy of that light to calculate the minimum frequency
Thu Oct 10, 2019 2:05 pm
Forum: Properties of Light
Topic: Speed of Light
Replies: 4
Views: 76

Re: Speed of Light

Yes, it only applies in a vacuum, but unless the question specifies otherwise, I think you can assume it applies
Thu Oct 10, 2019 2:03 pm
Forum: Photoelectric Effect
Topic: Kinetic Energy from the Photoelectric Effect
Replies: 5
Views: 68

Re: Kinetic Energy from the Photoelectric Effect

In a photoelectric experiment, the kinetic energy is also measured by a detector
Thu Oct 03, 2019 12:41 pm
Forum: Empirical & Molecular Formulas
Topic: Rounding for Formulas
Replies: 8
Views: 145

Re: Rounding for Formulas

This came up in our discussion today, and generally if it's within .1 of the whole integer you want to round to it's ok. You could round 2.9 to 3, for example.
Thu Oct 03, 2019 12:32 pm
Forum: Molarity, Solutions, Dilutions
Topic: Periodic Table & Formulas
Replies: 2
Views: 70

Re: Periodic Table & Formulas

My TA said in discussion today that we will be provided with a periodic table and an equation sheet. Hope that helps!
Thu Oct 03, 2019 12:28 pm
Forum: Balancing Chemical Reactions
Topic: State Symbols in Equations
Replies: 8
Views: 172

Re: State Symbols in Equations

It's a good idea to start writing the state symbols now so it becomes a habit. They are very useful for understanding what is physically happening in the reaction, and they may be required later on.
Thu Oct 03, 2019 12:25 pm
Forum: Balancing Chemical Reactions
Topic: Products of combustion reactions
Replies: 7
Views: 117

Re: Products of combustion reactions

I believe when you are told to write an equation for a combustion reaction, you assume the products will be CO2 and H2O. However, sometimes you will be given other products, like in homework problem M19.
Thu Oct 03, 2019 10:03 am
Forum: Empirical & Molecular Formulas
Topic: Empirical Formula Purpose
Replies: 13
Views: 314

Re: Empirical Formula Purpose

The empirical formula is not used in chemical equations because it only shows the simplest ratio of the atoms in the molecule, not the actual number of atoms present. It can be used, along with the molar mass of the molecule, to find the molecular formula, which does tell you the number of atoms pre...