Search found 101 matches

by Eva Zhao 4I
Mon Mar 09, 2020 1:24 pm
Forum: General Rate Laws
Topic: rate laws and graphs
Replies: 4
Views: 104

Re: rate laws and graphs

For your reference, here are the graphs showing the slope line trends and axes labels for each order of reaction:
Image
by Eva Zhao 4I
Mon Mar 09, 2020 1:18 pm
Forum: General Rate Laws
Topic: Rate constant k
Replies: 3
Views: 94

Re: Rate constant k

To add on, the rate constant, k, does have different units depending on what order the reaction is. The general rule is as follows for the units of k: 1/(Mn-1*t-1), where n is the order of the reaction.
by Eva Zhao 4I
Mon Mar 09, 2020 1:13 pm
Forum: General Rate Laws
Topic: Rate Constant Units
Replies: 3
Views: 51

Re: Rate Constant Units

To add on, the general rule for rate constant units is:
1/(Mn-1*t-1), where n is the order of the reaction.
by Eva Zhao 4I
Mon Mar 09, 2020 1:08 pm
Forum: General Rate Laws
Topic: Difference between each order of reaction
Replies: 3
Views: 24

Re: Difference between each order of reaction

Here's a general diagram with the given slope trend lines and axes labels for each type of order:
Image
by Eva Zhao 4I
Mon Mar 09, 2020 1:06 pm
Forum: General Rate Laws
Topic: First vs Second vs Zero Order
Replies: 7
Views: 29

Re: First vs Second vs Zero Order

Here's a digram with the given slope line trends and axes labels for each reaction order, if it helps:
Image
by Eva Zhao 4I
Mon Mar 02, 2020 2:17 pm
Forum: General Rate Laws
Topic: Order
Replies: 5
Views: 53

Re: Order

Here is a diagram of the graphs mentioned above, in case you might find it helpful:
Image
by Eva Zhao 4I
Mon Mar 02, 2020 2:11 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units for Gibbs
Replies: 3
Views: 36

Re: Units for Gibbs

As a general rule, anything with the ∆_ r is per mole. Regarding ∆G (according to the reply of a similar question), free energy can have the units of kJ or kJ/mol depending on whether the question refers to the molar free energy of a substance or the free energy of a specific amount of the substance...
by Eva Zhao 4I
Mon Mar 02, 2020 1:43 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Free Energy and Work
Replies: 5
Views: 58

Re: Free Energy and Work

Free energy is the maximum amount of energy from a system that can be used to perform useful work, in other words, work not associated with the expansion of a system.
by Eva Zhao 4I
Mon Mar 02, 2020 1:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: The sign of ∆Gº
Replies: 2
Views: 32

Re: The sign of ∆Gº

∆G˚ really tells you the thermodynamic favorability of a reaction using the ratio of the amount of product to the amount of reactant at equilibrium. Also, you are correct in the relationship shown by that equation; if ∆G˚is negative, then K>1 and it may be important to note that E˚ is positive.
by Eva Zhao 4I
Mon Mar 02, 2020 1:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Outline of Thermodynamics
Replies: 3
Views: 37

Re: Outline of Thermodynamics

Gibbs free energy, ΔG, is the maximum amount of energy from a system that can be used to perform useful work, in other words, work not associated with the expansion of a system.
by Eva Zhao 4I
Fri Feb 28, 2020 8:50 am
Forum: Balancing Redox Reactions
Topic: Oxidation Number
Replies: 2
Views: 26

Re: Oxidation Number

To add on, as a general rule, H is +1, O is generally -2 (except for peroxides), and halogens (i.e. F) are typically -1.
by Eva Zhao 4I
Fri Feb 28, 2020 8:36 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J.5
Replies: 2
Views: 35

Re: 4J.5

Yes, you're supposed to use ∆G˚=∆H˚-T∆S˚ with the values provided for ∆H˚ and ∆S˚ within that table. The purpose here is to show that the calculated answer should be pretty close to the actual ∆G˚ provided in that table, but it will likely be off by a few decimals.
by Eva Zhao 4I
Fri Feb 28, 2020 8:26 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Entropy units
Replies: 7
Views: 71

Re: Entropy units

As a general rule of thumb, try to write out the units as you're working through the problem since problems often give you a value in kJ, but the constants you use involve J. Otherwise unless the problem specifies, you can leave your answer in J or kJ. The answer key likely leaves the answer in kJ w...
by Eva Zhao 4I
Fri Feb 28, 2020 8:21 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Question 4J.7
Replies: 5
Views: 44

Re: Question 4J.7

Just to list a few more, H2, Cl2, Br2, and C(s, graphite) also have enthalpies of formation equal to 0.
by Eva Zhao 4I
Fri Feb 28, 2020 8:14 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Go=0
Replies: 7
Views: 51

Re: Go=0

∆G˚=0 when products and reactants are in their standard state and K=1. Note that this is not common.
by Eva Zhao 4I
Wed Feb 19, 2020 7:11 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: C in nCv ln (T2/T1)
Replies: 8
Views: 83

Re: C in nCv ln (T2/T1)

To add on, the relationship between Cv and Cp is Cp = Cv + 1. The values for Cv are shown below (know that we look at the ideal gas values):
Image
by Eva Zhao 4I
Wed Feb 19, 2020 7:04 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: U vs H
Replies: 15
Views: 146

Re: U vs H

To add on, the equation we often use to relate the two is ∆U = q + w. At constant pressure, ∆H = qp. Thus, we can rewrite the equation as ∆U = ∆H - P∆V when pressure is constant.
by Eva Zhao 4I
Wed Feb 19, 2020 6:58 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible Reaction
Replies: 6
Views: 74

Re: Reversible Reaction

Something to note is that the work a system can do is greatest in a reversible process, compared to an irreversible process. This is because a reversible process is one that can be reversed by an infinitely small change in a variable, i.e. pressure such that when a gas expands reversibly, the extern...
by Eva Zhao 4I
Wed Feb 19, 2020 6:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ∆G, ∆H, ∆S
Replies: 6
Views: 71

Re: ∆G, ∆H, ∆S

Here's a table that relates the three fairly well, with respect to T in order to determine spontaneity:
Image
by Eva Zhao 4I
Wed Feb 19, 2020 3:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: How to interpret reversible/irreversible graphs
Replies: 6
Views: 46

Re: How to interpret reversible/irreversible graphs

Something to note is that the work a system can do is greatest in a reversible process, hence the larger area under the curve for the reversible graph. The graphs are attached to this for your convenience. http://chemwiki.ucdavis.edu/@api/deki/files/9998/workdone.JPG?size=bestfit&width=454&h...
by Eva Zhao 4I
Mon Feb 10, 2020 2:13 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous delta G
Replies: 7
Views: 30

Re: Spontaneous delta G

For this problem, we're using the equation: ∆G˚ = ∆H˚ - T∆S˚. The key point to keep in mind here is that the reaction is spontaneous when ∆G˚ is negative. Thus, we're trying to find the temperature, T, at which T∆S˚ > ∆H˚ such that ∆G˚ is negative. To do so, we can set ∆G˚ = 0 to find the minimum te...
by Eva Zhao 4I
Mon Feb 10, 2020 1:48 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: S=kB*lnw equation
Replies: 4
Views: 431

Re: S=kB*lnw equation

To add on, the Boltzmann's constant, k = 1.38 x 10–23 J·K-1.
by Eva Zhao 4I
Mon Feb 10, 2020 1:32 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Is spontaneity determined by entropy or free energy?
Replies: 9
Views: 449

Re: Is spontaneity determined by entropy or free energy?

As others have said, check for whether the question is asking for ∆S or total entropy. That being said, a useful chart to check for spontaneity with ∆S, provided ∆H is given, is (through the use of ∆G = ∆H - T∆S): https://s3mn.mnimgs.com/img/shared/discuss_editlive/1643930/2012_01_23_14_07_42/FOR_2....
by Eva Zhao 4I
Mon Feb 10, 2020 1:14 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: What is residual entropy?
Replies: 11
Views: 945

Re: What is residual entropy?

To add on, the only time when a molecule would have no entropy is when you have a molecule at 0 K that’s perfectly ordered. Otherwise, molecules at 0 K would still have entropy due to the concept of residual entropy, which is explained by others above.
by Eva Zhao 4I
Mon Feb 10, 2020 1:09 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Why is delta U = 0 for isothermal reactions?
Replies: 11
Views: 117

Re: Why is delta U = 0 for isothermal reactions?

To add on, I believe the 3/2 in your equation came from 'Ideal gas, Cv = (3/2) R' (which can be found on the formula sheet). Note that this 'C' value varies depending on what you're trying to solve for, i.e. 'Ideal gas, Cp = (5/2) R'.
by Eva Zhao 4I
Mon Feb 03, 2020 1:50 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal Energy/Open System
Replies: 3
Views: 159

Re: Internal Energy/Open System

To clarify, adding or removing the amount of substance in a system correlates to changing the energy of an open system. Heating/cooling the system or doing work on the system are examples provided in class for a closed system.
by Eva Zhao 4I
Mon Feb 03, 2020 1:38 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated// Energy
Replies: 11
Views: 79

Re: Isolated// Energy

No, in an isolated system there can be no exchange of energy with the surrounding. The combustion of glucose in a bomb calorimeter is an example. To clarify, a closed system can have energy exchange with surroundings by heating/cooling or compression/expansion.
by Eva Zhao 4I
Mon Feb 03, 2020 1:22 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed Systems
Replies: 14
Views: 122

Re: Closed Systems

In a closed system, energy can be exchanged with surroundings, unlike an isolated system in which nothing can be exchanged with the surroundings. The energy of a closed system can be changed by heating/cooling or compression/expansion (i.e. compressing a piston).
by Eva Zhao 4I
Mon Feb 03, 2020 1:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed System
Replies: 7
Views: 66

Re: Closed System

Just to add on, other examples of closed systems that can be found in the textbook (4A.1) are:

1) A coolant in a refrigerator coil
2) Mercury in a thermometer
by Eva Zhao 4I
Mon Feb 03, 2020 1:12 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: closed vs isolated?
Replies: 7
Views: 45

Re: closed vs isolated?

An example of a closed system (energy can exchange with surroundings) is a sealed beaker of water, in which the beaker does not insulate. An example of an isolated system (nothing exchanges with surroundings) is the combustion of glucose in a bomb calorimeter. These are the examples provided in clas...
by Eva Zhao 4I
Mon Jan 27, 2020 1:29 pm
Forum: Phase Changes & Related Calculations
Topic: Unrelated
Replies: 3
Views: 370

Re: Unrelated

For evaporation to occur, the temperature does not necessarily need to reach the boiling point. One thing to keep in mind is that evaporation is a natural process (boiling usually isn't) and while similar to boiling, the water can change from liquid to vapor form when there is an increase in either ...
by Eva Zhao 4I
Mon Jan 27, 2020 1:16 pm
Forum: Phase Changes & Related Calculations
Topic: steam at 100ºC burn worse
Replies: 7
Views: 288

Re: steam at 100ºC burn worse

To help clarify with the help of the water heating curve, you can see in the diagram that it takes much more energy for liquid water to transition to steam than for ice to transition to liquid water. Thus, steam at 100ºC holds more energy than liquid water at 100ºC, causing worse burns. https://chem...
by Eva Zhao 4I
Mon Jan 27, 2020 1:12 pm
Forum: Phase Changes & Related Calculations
Topic: boiling points
Replies: 4
Views: 273

Re: boiling points

I found this diagram online which will hopefully help clarify things. You can see that it takes some time before the liquid is fully vaporized.

Image
by Eva Zhao 4I
Mon Jan 27, 2020 1:08 pm
Forum: Phase Changes & Related Calculations
Topic: Why does steam cause burns?
Replies: 29
Views: 171

Re: Why does steam cause burns?

Showing the actual diagram, which is the heating curve of water, you can see that it takes a lot more energy to transition from liquid to vapor than it does from solid to liquid. Therefore, steam carries much more heat for worse burns than boiling water. https://chem.libretexts.org/@api/deki/files/6...
by Eva Zhao 4I
Mon Jan 27, 2020 1:05 pm
Forum: Phase Changes & Related Calculations
Topic: Steam?
Replies: 8
Views: 75

Re: Steam?

For a more visual representation through the heating curve of water, you can see that transitioning from liquid to vapor requires a lot more energy than it does from solid to liquid. Thus, steam carries more heat than boiled water. https://chem.libretexts.org/@api/deki/files/61002/6c6b33a839c7613ad3...
by Eva Zhao 4I
Tue Jan 21, 2020 10:32 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and K
Replies: 8
Views: 126

Re: Q and K

Q and K are calculated essentially the same way. However, Q expresses the relative ratio of products to reactants at a given instant not necessarily at equilibrium, which is why you can compare Q and K to determine the direction of a reaction. The reaction shifts right if Q<K, shifts left if Q>K, an...
by Eva Zhao 4I
Tue Jan 21, 2020 10:28 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: units for pressure
Replies: 5
Views: 199

Re: units for pressure

My TA said bar would be the most likely unit used. However, it's always a good idea to check your units and ensure the correct cancelation.
by Eva Zhao 4I
Tue Jan 21, 2020 10:23 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 10
Views: 265

Re: Reaction Quotient

Q expresses the relative ratio of products to reactants at a given instant not necessarily at equilibrium, which is why you compare Q and K to determine the direction of the reaction. The reaction shifts right if Q<K, shifts left if Q>K, and is at equilibrium when Q=K.
by Eva Zhao 4I
Tue Jan 21, 2020 10:12 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Q
Replies: 7
Views: 47

Re: Reaction Q

Q expresses the relative ratio of products to reactants at a given instant not necessarily at equilibrium, which is why you can compare Q with K to determine the direction of the reaction. The reaction shifts right if Q<K, shifts left if Q>K, and is at equilibrium is Q=K.
by Eva Zhao 4I
Tue Jan 21, 2020 10:09 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Using Kc Vs Kp
Replies: 18
Views: 144

Re: Using Kc Vs Kp

Kp can only be used when reactants and products are gases. Kc can be used for gases or aqueous substances, but you should check the units involved to ensure you're using the right K.
by Eva Zhao 4I
Mon Jan 13, 2020 10:48 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Partial Pressure to Concentration
Replies: 3
Views: 84

Re: Partial Pressure to Concentration

Just to add on, when using PV=nRT, you can rearrange the formula as such: P=(n/V)RT. (n/V) then represents the concentration, mol/L, and using the constant R and the given temperature, you can convert between partial pressure and concentration.
by Eva Zhao 4I
Mon Jan 13, 2020 8:47 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constants
Replies: 4
Views: 561

Re: Equilibrium constants

Solids have an essentially constant concentration because they are practically incompressible. As a result, it takes enormous pressure to cause even a tiny reduction in volume. As such, solids can be excluded from the equilibrium constant.
by Eva Zhao 4I
Mon Jan 13, 2020 8:43 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: solids and liquids
Replies: 6
Views: 38

Re: solids and liquids

Liquids and solids have an essentially constant concentration because they are practically incompressible. As a result, it takes enormous pressure to cause even a tiny reduction in volume. As such liquids and solids can be excluded from the equilibrium constant.
by Eva Zhao 4I
Mon Jan 13, 2020 8:38 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q
Replies: 10
Views: 61

Re: Q

Q expresses the relative ratio of products to reactants at a given instant not necessarily at equilibrium. This is mainly useful to compare to K in order to determine the direction of the reaction. When Q=K, the system is at equilibrium.
by Eva Zhao 4I
Mon Jan 13, 2020 8:29 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K
Replies: 5
Views: 37

Re: Calculating K

Liquids and solids have an essentially constant concentration because they are practically incompressible. As a result, it takes enormous pressure to cause even a tiny reduction in volume. As such liquids and solids can be excluded from the equilibrium constant.
by Eva Zhao 4I
Thu Jan 09, 2020 9:40 pm
Forum: Ideal Gases
Topic: Difference between K and Q
Replies: 9
Views: 59

Re: Difference between K and Q

To add on, since Q expresses the relative ratio of products to reactants at a given instant not necessarily at equilibrium, you know the reaction shifts right if Q<K and shifts left if Q>K.
by Eva Zhao 4I
Thu Jan 09, 2020 9:29 pm
Forum: Ideal Gases
Topic: pressure [ENDORSED]
Replies: 13
Views: 234

Re: pressure [ENDORSED]

Yes, by PV=nRT, pressure (P) can be increased by increasing the temperature (T) or increasing the moles (n) of the substance involved (assuming no other variables are changed for simplicity's sake).
by Eva Zhao 4I
Thu Jan 09, 2020 9:25 pm
Forum: Ideal Gases
Topic: Ideal Gases
Replies: 7
Views: 150

Re: Ideal Gases

As others have mentioned, an ideal gas is theoretical. Most gases do behave closer to ideal with high temperature and low pressure, however. For most problems, unless stated otherwise, ideal gases should be the ones involved such that we can simplify calculations and use i.e. PV=nRT (ideal gas law).
by Eva Zhao 4I
Thu Jan 09, 2020 9:17 pm
Forum: Ideal Gases
Topic: Definition of Ideal Gases?
Replies: 3
Views: 80

Re: Definition of Ideal Gases?

Ideal gases have negligible volume, no attractive or repulsive forces, random movement, and perfectly elastic collisions. Most gases behave close to the ideal with high temperature and low pressure; hence an ideal gas is theoretical since PV=nRT shows that pressure typically increases with temperatu...
by Eva Zhao 4I
Thu Jan 09, 2020 9:05 pm
Forum: Ideal Gases
Topic: R in PV=nRT
Replies: 34
Views: 487

Re: R in PV=nRT

R is the universal gas constant, sometimes known as the Regnault constant. The value of the R constant is 8.3144598 J/mol·K.
by Eva Zhao 4I
Tue Dec 03, 2019 10:50 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 275
Views: 118799

Re: Saying Thank You to Dr. Lavelle

Dear Dr. Lavelle, Thank you for an incredible winter quarter! I really appreciate all of the resources you provide on your website and the many, many hours of review and study sessions you offer. You definitely help to build a stable foundation for future courses in chemistry. With that, I look forw...
by Eva Zhao 4I
Tue Dec 03, 2019 10:38 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Versus Lewis
Replies: 4
Views: 143

Re: Bronsted Versus Lewis

The Lewis definition is more consistent in classifying most acids-bases, since a molecule might not have hydrogen to donate for the definition of a Bronsted acid. However, my TA said, at least for now, the Bronsted definition will be primarily used (i.e. for writing chemical equations in acid-base r...
by Eva Zhao 4I
Tue Dec 03, 2019 10:32 pm
Forum: Bronsted Acids & Bases
Topic: Conjugate acids and bases
Replies: 5
Views: 49

Re: Conjugate acids and bases

Hopefully, this will help you visualize the acid-base pairings in a reaction (if you're a visual learner like me):

Image
by Eva Zhao 4I
Tue Dec 03, 2019 10:27 pm
Forum: Bronsted Acids & Bases
Topic: bronsted vs lewis
Replies: 2
Views: 31

Re: bronsted vs lewis

Just to add on, if you think of a Bronsted acid as donating a proton, it's consistent with the idea of receiving electrons by definition of a Lewis acid (donates H + , gets e- back). Apparently, the Lewis definitions are more consistent for most acids/bases, especially for those without hydrogen whe...
by Eva Zhao 4I
Tue Dec 03, 2019 10:14 pm
Forum: Bronsted Acids & Bases
Topic: Strong Acids and Bases
Replies: 4
Views: 45

Re: Strong Acids and Bases

I agree! Knowing strong acids and bases would be very helpful in writing out the equation or for calculations, especially for our current level of chemistry which focuses mainly on strong acids and bases. Table 6C.3 in the textbook, page 464, might be helpful.
by Eva Zhao 4I
Wed Nov 27, 2019 1:13 pm
Forum: Naming
Topic: Oxidation
Replies: 14
Views: 164

Re: Oxidation

To add on, if the problem asks for the oxidation number of the metal, use:
(# of metal ion)*(oxidation number) + (# if each ligand)*(charge of each ligand) = charge of ion

The charge of the ion should be given, allowing you to isolate and solve for the oxidation number of the metal.
by Eva Zhao 4I
Wed Nov 27, 2019 12:39 pm
Forum: Bronsted Acids & Bases
Topic: Strong acid
Replies: 6
Views: 370

Re: Strong acid

Strong acids almost completely ionize in solution. HCl, which dissociates completely, is a strong acid. Therefore, 0.1 M HCl(aq) implies 0.1 M H3O+(aq) and 0.1 M Cl-(aq).
by Eva Zhao 4I
Wed Nov 27, 2019 12:33 pm
Forum: Bronsted Acids & Bases
Topic: Definition
Replies: 5
Views: 61

Re: Definition

A Bronsted acid is a proton donor (i.e. HCl, HBr), while a Lewis acid is an electron acceptor (i.e. BF3, H+).
by Eva Zhao 4I
Wed Nov 27, 2019 12:27 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acids and Bases
Replies: 3
Views: 144

Re: Bronsted Acids and Bases

Bronsted acids are proton donors. I believe that H2SO3 is a Bronsted acid because it can donate a proton to become HSO3-, its conjugate base.
by Eva Zhao 4I
Wed Nov 27, 2019 12:01 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted acid
Replies: 9
Views: 419

Re: Bronsted acid

By definition, Bronsted acids are proton donors. HBr is a Bronsted acid because it can donate its H+, to which it would become Br-.
by Eva Zhao 4I
Fri Nov 22, 2019 12:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polarity
Replies: 7
Views: 78

Re: Polarity

To add on, a good rule of thumb is that if the structure is symmetrical, it's typically nonpolar, and if the structure is asymmetrical, it's typically polar. You may have to look at electronegativity differences and dipole-dipole interactions to check.
by Eva Zhao 4I
Fri Nov 22, 2019 12:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: bent v. angular
Replies: 20
Views: 216

Re: bent v. angular

Bent and angular refer to the same shape with VSEPR formulas AX2E or AX2E2.
by Eva Zhao 4I
Fri Nov 22, 2019 12:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polar vs non polar
Replies: 6
Views: 60

Re: polar vs non polar

To add on, sometimes you can tell just by looking at the formula where it may be obvious that hydrogen bonds are present, etc. Often times, it's better to draw out the structure to be sure, during which looking at the symmetry of the structure helps to determine whether or not it's polar/nonpolar. N...
by Eva Zhao 4I
Fri Nov 22, 2019 12:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Why is CH2Cl2 polar?
Replies: 12
Views: 119

Re: Why is CH2Cl2 polar?

To add on, typically speaking, a molecule with a tetrahedral shape is only nonpolar if all four atoms bonded to the central atom are the same.
by Eva Zhao 4I
Fri Nov 22, 2019 12:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Removing Non-Axis Atoms First
Replies: 4
Views: 40

Re: Removing Non-Axis Atoms First

Referencing back to the seesaw shape, the lone pair in the equatorial plane is removed first to minimize repulsion. By doing so, the more repulsive lone pair interacts with only 2 bonds at 90° instead of three bonds if the axial lone pair was removed. Hence, removing the lone pair in the equatorial ...
by Eva Zhao 4I
Sat Nov 16, 2019 8:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: What is VSPER
Replies: 14
Views: 193

Re: What is VSPER

VSEPR stands for Valence-Shell Electron-Pair Repulsion. The VSEPR Model explains the experimentally observed shape of molecules and can predict distortions qualitatively but not quantitatively. It may be helpful to memorize the shapes and general angles, though you probably don't need to memorize ex...
by Eva Zhao 4I
Sat Nov 16, 2019 8:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR
Replies: 2
Views: 200

Re: VSEPR

Lewis structures are 2-D representations of molecular shape and indicate the approximate location of bonding e- and lone pair e-. The VSEPR Model, or the Valence-Shell Electron-Pair Repulsion Model, explains the experimentally observed shape of molecules. Note that the VSEPR Model can predict distor...
by Eva Zhao 4I
Sat Nov 16, 2019 7:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: seesaw
Replies: 9
Views: 83

Re: seesaw

If you're a visual learner like I am, here's the image for SF4, AX4E with 4 bonding pairs and 1 lone pair:
Image
by Eva Zhao 4I
Sat Nov 16, 2019 7:56 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 8
Views: 70

Re: Bond Angles

Like what others have said, it will probably be helpful to memorize the angles. As a side note, trigonal planar angles are 120 degrees. The 107 degrees was for, i.e. NH3, a molecule with 1 lone pair and 3 bonding pairs.
by Eva Zhao 4I
Sat Nov 16, 2019 7:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar vs. Nonpolar
Replies: 12
Views: 117

Re: Polar vs. Nonpolar

While not always the case, symmetrical shapes typically indicate the molecule is nonpolar; there are dipole-dipole interactions, but they cancel out for a nonpolar molecule. Asymmetrical shapes typically indicate the molecular is polar since the dipole-dipole interactions can't cancel out.
by Eva Zhao 4I
Fri Nov 08, 2019 1:07 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic vs. Covalent
Replies: 4
Views: 599

Re: Ionic vs. Covalent

Just to add on, for the more in-between electronegativity differences, where it's uncertain whether the bonds are covalent or ionic, it's based on properties. For example, if the substance can dissociate in water, it may be more ionic in character.
by Eva Zhao 4I
Fri Nov 08, 2019 12:23 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum Numbers
Replies: 6
Views: 100

Re: Quantum Numbers

ms is usually pretty arbitrary unless the question specifies that the electron is +1/2 or -1/2. The most important thing to remember is that no two electrons in an atom can have the exact same four quantum numbers, so if one electron is +1/2, the other in the pair is -1/2.
by Eva Zhao 4I
Fri Nov 08, 2019 12:17 pm
Forum: Quantum Numbers and The H-Atom
Topic: Formal names for each letter
Replies: 5
Views: 102

Re: Formal names for each letter

n = Principle Quantum Number l = Angular Momentum Quantum Number m l = Magnetic Quantum Number m s = Spin Magnetic Quantum Number n defines l and m l and as such is the principle quantum number. For l, I tend to think of it as the odd one out; it's not the principle and it's not magnetic so it must ...
by Eva Zhao 4I
Fri Nov 08, 2019 12:03 pm
Forum: Quantum Numbers and The H-Atom
Topic: n, l ,ml, ms
Replies: 13
Views: 242

Re: n, l ,ml, ms

As mentioned, ms can be either +1/2 or -1/2, and it's pretty arbitrary unless the question specifically provides the spin. The most important thing to note is that no two electrons in the same atom can have the exact same four quantum numbers.
by Eva Zhao 4I
Fri Nov 08, 2019 12:00 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum numbers
Replies: 12
Views: 169

Re: Quantum numbers

To add on, the angular momentum quantum number (l), or the secondary quantum number, describes the shape of the orbital that an electron occupies with allowed values of n-1.
by Eva Zhao 4I
Sat Nov 02, 2019 9:16 pm
Forum: Quantum Numbers and The H-Atom
Topic: Angular Momentum Quantum Number
Replies: 3
Views: 72

Re: Angular Momentum Quantum Number

The Angular Momentum Quantum Number (l) describes shape by corresponding with a certain sub-shell, each of which with a unique arrangement. I hope this diagram will help you better picture what the second quantum number describes; note that not all possible variations of each sub-shell are shown in ...
by Eva Zhao 4I
Sat Nov 02, 2019 9:07 pm
Forum: Quantum Numbers and The H-Atom
Topic: Ms and ML
Replies: 6
Views: 73

Re: Ms and ML

Magnetic Quantum Number (m l ) labels different orbitals or sub-shells with allowed values of l, l-1,..., 0,..., -l. For example: l=2; m l can be -2, -1, 0, 1, 2 Spin Magnetic Quantum Number (m s ) denotes the spin of an electron with values of +1/2 or -1/2, depending on if the electron is spin up o...
by Eva Zhao 4I
Sat Nov 02, 2019 9:01 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum Number
Replies: 3
Views: 43

Re: Quantum Number

As said previously, the spin magnetic quantum number (ms) can be +1/2 or -1/2. It's usually pretty arbitrary, so long as you're aware that no two electrons in the same atom have the same four quantum numbers.
by Eva Zhao 4I
Sat Nov 02, 2019 8:58 pm
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Quantum Number
Replies: 5
Views: 47

Re: Magnetic Quantum Number

You would only say 5 if the question asks for the number of possible ml values. Otherwise, given that l=2, you can't say that 5 is a possible value of ml since the allowed values are l, l-1,..., 0,..., -l.
by Eva Zhao 4I
Sat Nov 02, 2019 8:51 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum Numbers
Replies: 7
Views: 87

Re: Quantum Numbers

The spin number, or the spin magnetic quantum number (m s ), is +1/2 or -1/2 since an electron can be spin up or down. The significance is that no two electrons in the same atom can have the same four quantum numbers. It tends to be pretty arbitrary as long as the combination of the four quantum num...
by Eva Zhao 4I
Thu Oct 24, 2019 5:18 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Hunds Rule
Replies: 2
Views: 326

Re: Hunds Rule

Here's a visual aid for Hund's Rule, which may help you understand a bit better (if you're visual learner like I am):

Image
by Eva Zhao 4I
Thu Oct 24, 2019 5:04 pm
Forum: Quantum Numbers and The H-Atom
Topic: Spin Quantum Number
Replies: 4
Views: 48

Re: Spin Quantum Number

An important thing to note with the inclusion of the spin quantum number is that no two electrons in the same atom can have exactly the same four quantum numbers. The spins are indicated, as everyone said, by +1/2 or -1/2 since the electron can spin up or down.
by Eva Zhao 4I
Thu Oct 24, 2019 5:02 pm
Forum: Quantum Numbers and The H-Atom
Topic: Orbital Angular Momentum
Replies: 3
Views: 35

Re: Orbital Angular Momentum

The angular momentum quantum number (l) describes "shape" and is also known as the sub-shell. The allowed values are l = 0,1,2,...,n-1. Note that n is the principle quantum number which determines energy and size, or shells.

l = 0 s-orbital
l = 1 p-orbital
l = 2 d-orbital
l = 3 f-orbital
by Eva Zhao 4I
Wed Oct 23, 2019 9:55 am
Forum: Properties of Light
Topic: Photons
Replies: 3
Views: 45

Re: Photons

Hello! Just to add on a little more information, certain energy formulas will not work for photons due to photons having zero mass. E=mc^2, for example, will not work for the photon as it would for an electron; photons have energy, yet the formula E=mc^2 would result in an answer of 0 J for the phot...
by Eva Zhao 4I
Wed Oct 23, 2019 9:40 am
Forum: Properties of Light
Topic: Destructive Interference
Replies: 3
Views: 56

Re: Destructive Interference

Just to add on, destructive interference occurs when waves come together in a way that they cancel each other out. While usually in between for a result of smaller amplitude, destructive interference can produce zero amplitude in the right conditions. Note that when two waves interfere destructively...
by Eva Zhao 4I
Wed Oct 16, 2019 5:25 pm
Forum: Photoelectric Effect
Topic: Work function units
Replies: 4
Views: 319

Re: Work function units

Just to add on: the work function is the energy needed to remove an electron, also known as the threshold energy. The unit for energy is J (joule); as such, the unit for work function is J.
by Eva Zhao 4I
Wed Oct 16, 2019 4:58 pm
Forum: SI Units, Unit Conversions
Topic: Joules
Replies: 2
Views: 39

Re: Joules

The SI units for Joules (J) are kg * m^2 * s^-2. Not sure if this will be the best method to help you, but my TA explained how he remembers the SI units for Joule: W = F * d; where W is work (unit is J), F is force, and d is distance = [m(a)] * d; since F=ma = [kg(m*s^-2)] * m; where kg is SI unit f...
by Eva Zhao 4I
Wed Oct 16, 2019 4:46 pm
Forum: SI Units, Unit Conversions
Topic: Conversion
Replies: 2
Views: 42

Re: Conversion

I agree with the previous post! Just to make it clearer (if you're a visual learner like I am): \frac{2.26*10^-46 m}{1} * \frac{1 nm}{1*10^-9 m} Since meters (m) is in both the numerator and denominator, you can cross them out. Then you'll be left with nanometers (nm), the unit you want. Again, conv...
by Eva Zhao 4I
Wed Oct 16, 2019 2:38 pm
Forum: Quantum Numbers and The H-Atom
Topic: spin magnetic quantum number
Replies: 3
Views: 77

Re: spin magnetic quantum number

Just to add on to previous replies, the spin magnetic quantum number was deemed necessary after the Stern and Gerlach Experiment, where the electrons were found to have two different spins (hence +1/2 or -1/2). It's important to note that no two electrons in the same atom have the same four quantum ...
by Eva Zhao 4I
Wed Oct 16, 2019 2:10 pm
Forum: Properties of Light
Topic: Lyman Series & Balmer Series
Replies: 4
Views: 43

Re: Lyman Series & Balmer Series

Just to add on, the Balmer Series corresponds to visible light, n1=2; Lyman series corresponds to ultraviolet light, n1=1. This is good to know for some problems that just provide what type of electromagnetic radiation is involved, i.e. 1A.15.
by Eva Zhao 4I
Sat Oct 12, 2019 1:13 am
Forum: SI Units, Unit Conversions
Topic: Conversion
Replies: 6
Views: 251

Re: Conversion

The unit for joules (J) in SI units is kg⋅m^2⋅s^−2. Like what others have said, meters and joules are units of measure for different criteria; meters are units of length and joules are units of energy. A possible equation that relates the two is: Kinetic energy = 1/2 * mass * velocity ^2.
by Eva Zhao 4I
Sat Oct 12, 2019 12:56 am
Forum: SI Units, Unit Conversions
Topic: knowing how many sig figs to use
Replies: 17
Views: 207

Re: knowing how many sig figs to use

To keep your work as accurate as possible, try not to round until the final answer. On the basis that you do round, keeping a certain number of significant figures should be enough to result in the final answer. For example, if the answer needs to have two significant figures, keeping four significa...
by Eva Zhao 4I
Sat Oct 12, 2019 12:52 am
Forum: SI Units, Unit Conversions
Topic: Formula units vs molecule
Replies: 7
Views: 122

Re: Formula units vs molecule

Formula units work the same way as do molecules and atoms through Avogadro's number. According to the book, the key difference is that formula units pertain to ionic compounds, whereas molecules are of molecular compounds and atoms are of elements. If you want to check it out yourself, the informati...
by Eva Zhao 4I
Sat Oct 12, 2019 12:41 am
Forum: Balancing Chemical Reactions
Topic: Writing an Equation for the Reaction
Replies: 9
Views: 2080

Re: Writing an Equation for the Reaction

Just to add onto the topic of combustion, O2 (oxygen gas) is reacted with the given fuel for the products of CO2 (carbon dioxide) and H2O (water). Depending on the fuel, you may need to balance the equation.
by Eva Zhao 4I
Sat Oct 12, 2019 12:33 am
Forum: SI Units, Unit Conversions
Topic: Practice Problems?
Replies: 11
Views: 216

Re: Practice Problems?

There is a list of practice problems, for fundamentals and further topics, on the class syllabus. Just scroll down to the last pages.

Here's the link: https://lavelle.chem.ucla.edu/wp-conten ... SYLL_1.pdf
by Eva Zhao 4I
Fri Oct 04, 2019 10:30 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E.16
Replies: 2
Views: 56

Re: E.16

Thanks!
by Eva Zhao 4I
Fri Oct 04, 2019 3:59 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Avogadro's number
Replies: 9
Views: 116

Re: Avogadro's number

Avogadro's number, 6.022 x 10^23, represents the number of "particles" within one mole of a substance. These particles can be, for example, the number of atoms per mole of a given compound.
by Eva Zhao 4I
Fri Oct 04, 2019 3:54 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Rounding
Replies: 12
Views: 245

Re: Rounding

It's best to only round at the end of the calculations. If you round throughout the series of calculations, the answer could be different depending on the number of significant figures needed. Generally speaking, using 7 instead of 6.94 for Lithium can likely get you the right answer for say multipl...
by Eva Zhao 4I
Fri Oct 04, 2019 3:47 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Theoretical vs. Actual Yield
Replies: 38
Views: 1266

Re: Theoretical vs. Actual Yield

Theoretical yield is the amount of product that can be obtained if a chemical reaction has 100% efficiency, the maximum amount of yield possible. Actual yield is the amount of product actually produced by the reaction. Due to side reactions, impurities, some of the product sticking on to the sides o...
by Eva Zhao 4I
Fri Oct 04, 2019 3:39 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E.16
Replies: 2
Views: 56

E.16

E.16 The molar mass of the metal oxide M2O is 231.74 g.mol^-1. What is the molar mass of the chloride of this metal?

For this question, what exactly is the chloride within M2O, and how would you go about finding the molar mass of said chloride?

Go to advanced search