Search found 82 matches

by andrewcj 2C
Tue Feb 18, 2020 2:40 am
Forum: Administrative Questions and Class Announcements
Topic: Is this course curved?
Replies: 4
Views: 31

Re: Is this course curved?

From what I can gather, the midterm was quite difficult for most people, so there's a chance a few points may be added to normalize the grades of the class.
by andrewcj 2C
Tue Feb 18, 2020 2:39 am
Forum: Balancing Redox Reactions
Topic: Odd number of electrons
Replies: 3
Views: 40

Re: Odd number of electrons

It shouldn't happen, I don't think. In redox reactions we tend to focus on individual atoms being reduced or oxidized, so it shouldn't share electrons.
by andrewcj 2C
Tue Feb 18, 2020 2:37 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Nerves
Replies: 7
Views: 45

Re: Midterm Nerves

Something I found helpful on the amphetamines problem was to list what you know. It helped me get insight on how to approach the problem, even when the solution wasn't obvious.
by andrewcj 2C
Tue Feb 18, 2020 2:36 am
Forum: Administrative Questions and Class Announcements
Topic: Test 2
Replies: 11
Views: 30

Re: Test 2

It won't be cumulative. I believe it picks up from Gibbs free energy.
by andrewcj 2C
Tue Feb 18, 2020 2:35 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G vs. delta G naught
Replies: 6
Views: 20

Re: delta G vs. delta G naught

delta G naught is under standard conditions. if conditions are not standard, use delta G.
by andrewcj 2C
Sun Feb 09, 2020 12:55 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework 4A7
Replies: 2
Views: 18

Re: Homework 4A7

When the question says "its", it is referring to the entire system, which includes the kettle and the water.
by andrewcj 2C
Sun Feb 09, 2020 12:51 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Confused about Heat of Combustion
Replies: 2
Views: 12

Re: Confused about Heat of Combustion

I don't think you need to memorize this. This is just saying the heat of combustion for x moles of ethane = moles of ethane * (heat of combustion/1 mole of ethane).
by andrewcj 2C
Sun Feb 09, 2020 12:48 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Irreversible and Reversible Processes
Replies: 2
Views: 18

Re: Irreversible and Reversible Processes

In an irreversible process, heat is transferred out of the system, which increases the entropy of the universe. However, in reversible processes, theoretically, no heat is lost, which means the entropy of the universe does not change.
by andrewcj 2C
Sun Feb 09, 2020 12:45 am
Forum: Phase Changes & Related Calculations
Topic: 4C.13
Replies: 1
Views: 22

Re: 4C.13

The transfer of heat only stops when both objects are at the same temperature. This means the ice will continue to gain heat until it is melted and at the same temp as the water, or the water has frozen over and is the same temp as the ice. Since I'm assuming the water won't freeze, energy will be c...
by andrewcj 2C
Sun Feb 09, 2020 12:43 am
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: Entropy vs. moles
Replies: 3
Views: 8

Re: Entropy vs. moles

Yes, if you add matter to a system, the entropy will increase. More moles means more molecules which means more microstates for the molecules to be in.
by andrewcj 2C
Wed Jan 29, 2020 10:32 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: approximation
Replies: 4
Views: 15

Re: approximation

I assume you're referring to calculations using equilibrium constants. If the equilibrium constant you are using is less than 10 -3 , you can usually assume that subtracting x does not change a constant very much. However, this does not mean that x is zero. For example, if given 10 -5 = x 2 /(0.15-x...
by andrewcj 2C
Wed Jan 29, 2020 10:28 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Moles
Replies: 8
Views: 24

Re: Moles

Make sure you only count gaseous moles though, as liquids and solids are not noticeably affected by pressure changes to the equilibrium.
by andrewcj 2C
Wed Jan 29, 2020 10:01 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Calorimeters as Isolated Systems
Replies: 2
Views: 22

Re: Calorimeters as Isolated Systems

In a bomb calorimeter, the item being burned is considered part of the system. An isolated system cannot exchange matter and energy with its surroundings, but it can exchange matter and energy within itself.
by andrewcj 2C
Wed Jan 29, 2020 9:55 am
Forum: Phase Changes & Related Calculations
Topic: Steam burn and ice burns
Replies: 1
Views: 26

Re: Steam burn and ice burns

The heat from the burned skin would be transferred to the ice cube by conduction, and the ice cube would begin to melt. However, if it were applied after the skin was already burned, there would already be tissue damage, and the ice cube wouldn't reverse the burn.
by andrewcj 2C
Wed Jan 29, 2020 9:50 am
Forum: Phase Changes & Related Calculations
Topic: Phase change and temp
Replies: 8
Views: 24

Re: Phase change and temp

It is important to distinguish between breaking bonds and breaking the intermolecular attractions between molecules in a substance. During phase changes, the chemical bonds in the molecules of the substance aren't actually being broken. Rather, the energy added is being used to break the attractions...
by andrewcj 2C
Sat Jan 25, 2020 1:38 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculation methods
Replies: 6
Views: 16

Re: Calculation methods

How is method 4 different than method 3?
by andrewcj 2C
Sat Jan 25, 2020 1:36 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: exothermic reactions
Replies: 19
Views: 70

Re: exothermic reactions

Using Le'Chatlier's principle, the system will work to counteract the changes brought upon it. Therefore, heating the reaction favors the reactants, as this uses up the heat. Conversely, cooling the reaction favors the products, as it would release heat, restoring the initial state.
by andrewcj 2C
Sat Jan 25, 2020 1:34 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: k<10^-3
Replies: 9
Views: 35

Re: k<10^-3

Something to remember is that strong acids don't have K values. In the k expression, the denominator would be essentailly 0, which is an invalid expression.
by andrewcj 2C
Sat Jan 25, 2020 1:31 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When to use Standard enthalpies of formation
Replies: 3
Views: 22

Re: When to use Standard enthalpies of formation

To account for non-standard conditions, you just add the enthalpy changes required to get the reactants into their respective states in the conditions given.
by andrewcj 2C
Sat Jan 25, 2020 1:26 am
Forum: Phase Changes & Related Calculations
Topic: Bond Enthalpies
Replies: 5
Views: 25

Re: Bond Enthalpies

The second way Dr. Lavelle suggested to measure the enthalpy of a reaction was to use bond enthalpies. Essentially, you would find how much energy is required to break every bond in the reactants and add how much energy is released when every bond in the products is formed. However, a shortcut is to...
by andrewcj 2C
Tue Jan 14, 2020 11:00 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp vs Kc
Replies: 4
Views: 22

Re: Kp vs Kc

It is important to remember that because of the Ideal Gas Law, gases in equilibrium have concentrations proportional to their partial pressures. This is why both may be used in equilibrium constant calculations, although not with each other.
by andrewcj 2C
Tue Jan 14, 2020 10:58 pm
Forum: Ideal Gases
Topic: Law of Mass Action
Replies: 3
Views: 34

Re: Law of Mass Action

In short, the Law of Mass Action just states that for a set temperature, the equilibrium constant K does not change.
by andrewcj 2C
Tue Jan 14, 2020 10:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant
Replies: 4
Views: 14

Re: Equilibrium Constant

What exactly do you mean by aqueous solution? From what I understand, we include ions in solution in equilibrium constants. However, pure liquids and solids are excluded because they have an activity of 1, and equilibrium constants are technically calculated with activity, not concentration.
by andrewcj 2C
Tue Jan 14, 2020 10:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When to approximate
Replies: 5
Views: 31

Re: When to approximate

I'm not sure if this rule applies in this class, but my TA gave out a worksheet today in which we were supposed to approximate that subtracting X from a concentration doesn't change the concentration. The worksheet asks for you to check if the concentration of the product, or X, was less than 5% of ...
by andrewcj 2C
Tue Jan 14, 2020 10:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Chart
Replies: 5
Views: 19

Re: ICE Chart

If you see reverse and forwards reactions as arbitrary, I think it makes ICE tables easier. There is not a universal way to tell which way of a reaction is forward, it just depends on how its written. If ICE tables make sense to you for forwards reactions, just imagine the reverse reaction as the fo...
by andrewcj 2C
Fri Jan 10, 2020 1:20 am
Forum: Ideal Gases
Topic: Adding reactions
Replies: 4
Views: 20

Re: Adding reactions

When adding chemical equations, the reactants stay reactants and the products stay products. Therefore, in the combined equation, all reactants would be in the denominator and would be multiplied together. A similar logic can be applied to the products for the numerator. This is equivalent to multip...
by andrewcj 2C
Fri Jan 10, 2020 1:16 am
Forum: Ideal Gases
Topic: PV=nRT equation manipulation
Replies: 13
Views: 81

Re: PV=nRT equation manipulation

If there were, would that be a problem? Assuming the gas constant R was given in the correct units and the temperature was specified, I would think there would be enough information to solve a problem even if both partial pressures and concentrations were part of the information provided.
by andrewcj 2C
Fri Jan 10, 2020 1:14 am
Forum: Ideal Gases
Topic: 5G.11
Replies: 6
Views: 22

Re: 5G.11

Yes, the reaction quotient Q can indicate the direction of the reaction by comparing it to K. If Q < K, then the products side is favored and the forward reaction will proceed, and vice versa if Q > K.
by andrewcj 2C
Wed Jan 08, 2020 9:19 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure changes to equilibrium equations
Replies: 5
Views: 42

Re: Pressure changes to equilibrium equations

I think that increasing the partial pressure of a gas that doesn't participate in a reaction such as He has a similar effect as increasing the pressure of the system, assuming the volume of the reaction vessel is kept constant. If the partial pressure of He is increased without any of the other part...
by andrewcj 2C
Tue Jan 07, 2020 12:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: AV Mods Chem Equilibrium Part 1B Post Exam [ENDORSED]
Replies: 2
Views: 68

AV Mods Chem Equilibrium Part 1B Post Exam [ENDORSED]

In the post exam, there is a question 19b, but no question 19a. However, the question references the previous part, and doesn't provide sufficient information to solve it in its current form. I also tried using figures from question 18, but the answer I got does not match any of the available choice...
by andrewcj 2C
Thu Dec 05, 2019 8:41 pm
Forum: Conjugate Acids & Bases
Topic: Double Arrows
Replies: 3
Views: 28

Re: Double Arrows

It is always used in equilibriums to show a dynamic constant state of simultaneous reaction.
by andrewcj 2C
Thu Dec 05, 2019 2:08 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: CH4 versus CCl4 (Boiling Point)
Replies: 3
Views: 20

Re: CH4 versus CCl4 (Boiling Point)

CH 4 has weaker London forces than CCl 4 because it is smaller and has fewer electrons, which means the intermolecular forces in CH 4 are weaker than those in CCl 4 since both molecules are nonpolar. This means it takes less energy to break the attractions between molecules in a sample of CH 4 , res...
by andrewcj 2C
Thu Dec 05, 2019 2:04 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: using Ka and Pka
Replies: 4
Views: 27

Re: using Ka and Pka

i think for 14A, you only need to know how to calculate those values. In 14B, you can use those values in calculations and potentially get other values such as pH from Ka and pKa, but for now you don't need to worry about that.
by andrewcj 2C
Thu Dec 05, 2019 2:02 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: chelate
Replies: 3
Views: 25

Re: chelate

As I understand it,if a complex has the central metal atom as a part of a ring, it is a chelate.
by andrewcj 2C
Thu Dec 05, 2019 1:45 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Acid/Base Trends
Replies: 6
Views: 47

Re: Acid/Base Trends

Why is HF a weaker acid than HI? When an acid dissociates, the bond must be broken between the H + and the conjugate base. If the bond is strong, which it is in the case of HF, this makes it harder and less of the acid dissociates, resulting in less H + present in the resulting solution and a highe...
by andrewcj 2C
Fri Nov 29, 2019 3:13 am
Forum: Conjugate Acids & Bases
Topic: Acids and Bases
Replies: 10
Views: 58

Re: Acids and Bases

More generally, equilibrium arrows are used whenever there is an equilibrium present. This can be in reactions involving acids and bases, or just any reaction in general that can have an equilibrium such as the equilibrium between NO2 and N2O4.
by andrewcj 2C
Fri Nov 29, 2019 3:11 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: calculating pKa and pKb
Replies: 2
Views: 35

Re: calculating pKa and pKb

The conjugate acid is [C5H5NH]+.
by andrewcj 2C
Fri Nov 29, 2019 3:07 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Acid Strength
Replies: 6
Views: 41

Re: Acid Strength

It's worth noting that while H2SO4 is a strong acid, once it gives off its first proton, it becomes a weak acid. The HSO4- ion acts as a weak acid, as while it can give off its second proton, it usually doesn't.
by andrewcj 2C
Fri Nov 29, 2019 3:04 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Strength and Weakness
Replies: 12
Views: 327

Re: Strength and Weakness

I feel like this is obvious, but it hasn't been mentioned so I'll say it. You can also compare pH (lower pH means stronger acid).
by andrewcj 2C
Fri Nov 29, 2019 3:03 am
Forum: Lewis Acids & Bases
Topic: HCl vs HF
Replies: 19
Views: 98

Re: HCl vs HF

Bond strengths is the most-correct reason that HCl is a stronger acid compared to HF. If we only consider electronegativity, we only focus on how strongly F can pull H's electron, which doesn't necessarily imply how easy it is to pull the proton off of HF.
by andrewcj 2C
Fri Nov 22, 2019 2:23 am
Forum: Determining Molecular Shape (VSEPR)
Topic: AXE Format
Replies: 34
Views: 122

Re: AXE Format

I don't think it matters, as if you don't, common sense tells you that the subscript is 1, and if you do, you definitely wouldn't get marked down for it.
by andrewcj 2C
Fri Nov 22, 2019 2:22 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Test 2
Replies: 14
Views: 110

Re: Test 2

knowing bond angles of vsepr structures and how lone pairs can affect those bond angles is probably a good idea
by andrewcj 2C
Fri Nov 22, 2019 2:19 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape of Diatomic Molecules
Replies: 5
Views: 33

Re: Shape of Diatomic Molecules

do diatomic molecules have a bond angle?
by andrewcj 2C
Fri Nov 22, 2019 2:15 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Transplatin
Replies: 3
Views: 25

Re: Transplatin

The fact that transplatin can't bind to DNA means that it doesn't stop replication, which is the purpose of chemotherapy drugs.
by andrewcj 2C
Thu Nov 14, 2019 9:30 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: why are double bonds equally weighted as single ones when drawing models?
Replies: 10
Views: 63

Re: why are double bonds equally weighted as single ones when drawing models?

No. It's important to remember that in molecules with both single and multiple bonds, there only exist hybrid bonds of equal energy, and the localized double bonds depicted in lewis structures only exist as a limitation of lewis structures. This is why resonance structures exist: because the multipl...
by andrewcj 2C
Thu Nov 14, 2019 9:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing Molecular Structures
Replies: 8
Views: 39

Re: Drawing Molecular Structures

It's important to remember that the shaded/dashed triangles still represent bonds, just they help show a 3D shape in 2D.
by andrewcj 2C
Thu Nov 14, 2019 9:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Name
Replies: 17
Views: 122

Re: Molecular Shape Name

Some shapes come from others, so it might not be necessary to explicitly memorize every shape. For example, bent comes from a tetrahedral shape with 2 lone pairs, but you don't have have to necessarily memorize bent. Instead, just think about a tetrahedral shape and remove 2 atoms.
by andrewcj 2C
Thu Nov 14, 2019 9:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR Formula
Replies: 2
Views: 24

Re: VSEPR Formula

Generally, an A represents the central atom, an X represents an atom bonded to it, and an e represents a lone pair. For example, the formula of a tetrahedral shape would be AX4, and the formula for a bent shape would be AX2e2.
by andrewcj 2C
Thu Nov 14, 2019 9:06 pm
Forum: Dipole Moments
Topic: Dipole Moment to figure out polarity
Replies: 3
Views: 23

Re: Dipole Moment to figure out polarity

A good way to think about this is to compare a known polar molecule to a known nonpolar molecule. Take H 2 O and CH 4 for example. We know water is polar, and we can see that the net dipole moments do not cancel, and the molecule is left with a positive dipole by the hydrogen atoms and a negative di...
by andrewcj 2C
Fri Nov 08, 2019 2:20 am
Forum: Lewis Structures
Topic: Drawing Lewis Structures
Replies: 18
Views: 76

Re: Drawing Lewis Structures

I learned that you should try to minimize the absolute charge on the atoms in the molecule/ion. Therefore, if an ion has an overall +1 charge, it should be achieved by 0 charges and a single +1 charge, instead of say a -3 and a +4 charge.
by andrewcj 2C
Fri Nov 08, 2019 2:18 am
Forum: Lewis Structures
Topic: Formal Charges
Replies: 15
Views: 65

Re: Formal Charges

Recall the rules for drawing Lewis structures. The central atom is the one that is the least electronegative, which means it has the least electron pulling power. Therefore, it would probably be best for it to not have a negative charge.
by andrewcj 2C
Fri Nov 08, 2019 2:17 am
Forum: Octet Exceptions
Topic: General principles of octet exception
Replies: 7
Views: 39

Re: General principles of octet exception

The expanded octet comes from access to d orbitals, which can be used to create additional bonds to the 4 allowed by the s and p orbitals. In general, if an atom in a molecule can achieve a lower formal charge and make the molecule have a more logical formal charge by making more than 4 bonds (there...
by andrewcj 2C
Fri Nov 08, 2019 2:15 am
Forum: Octet Exceptions
Topic: Lewis Acids and Bases?
Replies: 11
Views: 76

Re: Lewis Acids and Bases?

A friend gave me the mnemonic "Lewis has e" which reminds me that Lewis acids and bases focus on electron exchange. After this, I just think about H+, which is acidic, and how it can accept electrons. Therefore, Lewis acids are electron acceptors.
by andrewcj 2C
Fri Nov 08, 2019 2:13 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm --> Final Concepts
Replies: 3
Views: 34

Re: Midterm --> Final Concepts

I believe the final is cumulative, but it is generally a good idea to remember the concepts covered so far, as they may come up in future chem classes.
by andrewcj 2C
Fri Nov 01, 2019 3:04 am
Forum: Lewis Structures
Topic: Best way to go about drawing Lewis structures
Replies: 7
Views: 57

Re: Best way to go about drawing Lewis structures

I suppose the trial and error gets easier with experience, as it is possible to identify patterns such as certain functional groups or complex ions in a structure.
by andrewcj 2C
Fri Nov 01, 2019 2:58 am
Forum: Electronegativity
Topic: electronegative
Replies: 6
Views: 33

Re: electronegative

If one atom is more electronegative than the other, the electrons will spend more time on average around that atom, and the character of the bond would become more ionic.
by andrewcj 2C
Fri Nov 01, 2019 2:57 am
Forum: Resonance Structures
Topic: hybrid structure
Replies: 4
Views: 37

Re: hybrid structure

Be wary of resonance structures any time you see a multiple bond, as you just have to think about if you could put the multiple bond somewhere else.
by andrewcj 2C
Fri Nov 01, 2019 2:54 am
Forum: Octet Exceptions
Topic: Exceptions to the Octet Rule Question
Replies: 3
Views: 19

Re: Exceptions to the Octet Rule Question

They do not always violate the octet rule. A simple counterexample would be HCl, which follows the rule.
by andrewcj 2C
Fri Nov 01, 2019 2:51 am
Forum: Ionic & Covalent Bonds
Topic: Electronegativity
Replies: 7
Views: 41

Re: Electronegativity

A trick I use is to just memorize that fluorine is the most electronegative element, and note its position on the periodic table.
by andrewcj 2C
Fri Oct 25, 2019 1:05 am
Forum: Bond Lengths & Energies
Topic: Bond lengths
Replies: 15
Views: 142

Re: Bond lengths

Debora Fernandez Clemente_ 4H wrote:would the bond length vary when it is a double or triple bond?

Yes! Multiple bonds will be shorter than single bonds.
by andrewcj 2C
Fri Oct 25, 2019 1:03 am
Forum: Ionic & Covalent Bonds
Topic: Electron Affinity
Replies: 5
Views: 44

Re: Electron Affinity

While my high school AP Chem teacher emphasized that this is a very unscientific way to think about it, I think it makes sense to think about electron affinity as how badly a neutral atom "wants" an electron. So for elements such as fluorine, which is so close to achieving a stable noble g...
by andrewcj 2C
Fri Oct 25, 2019 12:59 am
Forum: Trends in The Periodic Table
Topic: Homework Question 1F.19
Replies: 5
Views: 41

Re: Homework Question 1F.19

Does anyone else find the wording a little ambiguous? Because I think you can make the argument that fluorine is extremely reactive too, due to how close it is to a noble gas electron configuration, but fluorine is definitely not an s-block metal. In this case, fluorine readily takes electrons from ...
by andrewcj 2C
Fri Oct 25, 2019 12:46 am
Forum: Ionic & Covalent Bonds
Topic: Resonance
Replies: 12
Views: 94

Re: Resonance

Another way to look at this (I think) is to look at bond order. If a molecule has resonance, its bond order will be higher than a molecule with only single bonds. In other words, its "average" bond strength will be in between that of a single bond and a double bond, and since multiple bond...
by andrewcj 2C
Mon Oct 21, 2019 1:47 pm
Forum: Properties of Electrons
Topic: Problem 1E.5
Replies: 3
Views: 39

Problem 1E.5

I'm having a little trouble with problem 1E.5. It reads as follows: Which of the following statements are true for many-electron atoms? If false, explain why. (a) The effective nuclear charge Z eff is independent of the number of electrons present in an atom. (b) Electrons in an s-orbital are more e...
by andrewcj 2C
Fri Oct 18, 2019 1:41 am
Forum: Einstein Equation
Topic: Mass of a proton and neutron
Replies: 3
Views: 21

Re: Mass of a proton and neutron

I believe there's a table on Lavelle's course website with those masses.
by andrewcj 2C
Fri Oct 18, 2019 1:38 am
Forum: Properties of Light
Topic: 1A9 Table
Replies: 2
Views: 28

Re: 1A9 Table

Reading involves visible light.
Getting a dental x-ray involves x-rays.
Using a microwave results in microwave radiation.
Tanning involves UV rays.
by andrewcj 2C
Fri Oct 18, 2019 1:34 am
Forum: Einstein Equation
Topic: Joules units
Replies: 6
Views: 103

Re: Joules units

In the formula E = hv, E is measured in Joules and v is measured in Hz, or s^-1. By dimensional analysis, we see that by multiplying kg x m^2 / s by 1/s, we get a units of kg x m^2/s^2. Since Joules is a measure of energy/work, it is equivalent to force x distance. Breaking this down further, force ...
by andrewcj 2C
Fri Oct 18, 2019 1:25 am
Forum: Photoelectric Effect
Topic: Problem 1B.3
Replies: 4
Views: 34

Re: Problem 1B.3

Part of the experiment demonstrating the photoelectric effect revealed that more electrons can be ejected from metal by shining light on it if the wavelength of the light was increased. If light was viewed as a wave, we would expect increasing intensity to correlate to more electrons being ejected. ...
by andrewcj 2C
Fri Oct 18, 2019 1:22 am
Forum: Properties of Light
Topic: Unit for Wavelength
Replies: 34
Views: 164

Re: Unit for Wavelength

Wavelength refers to the length of a wave, which is measured in meters. Just in case you needed the conversions, 1 nm = 10^-9 m. I also think that these conversions will be provided on tests.
by andrewcj 2C
Fri Oct 11, 2019 1:41 am
Forum: Limiting Reactant Calculations
Topic: Theoretical yield
Replies: 5
Views: 89

Re: Theoretical yield

Dimensional analysis will reveal that the units cancel out, and you end up with an answer in grams when you multiply the 2 quantities.
by andrewcj 2C
Fri Oct 11, 2019 1:40 am
Forum: Quantum Numbers and The H-Atom
Topic: Atomic Spectra Question
Replies: 3
Views: 38

Re: Atomic Spectra Question

I thought it was by wavelength, not frequency, although I guess because they're proportional it doesn't matter.
by andrewcj 2C
Fri Oct 11, 2019 1:36 am
Forum: Properties of Light
Topic: Emission/line spectrum
Replies: 3
Views: 18

Re: Emission/line spectrum

I think in the future, we may be asked what color a specific wavelength of light given off is (i.e if an electron emits a photon with a wavelength of 400, what color is the light?)
by andrewcj 2C
Fri Oct 11, 2019 1:34 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in Speed [ENDORSED]
Replies: 18
Views: 1219

Re: Uncertainty in Speed [ENDORSED]

One additional thing for my reply, make sure you convert nm to m.
by andrewcj 2C
Fri Oct 11, 2019 1:33 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in Speed [ENDORSED]
Replies: 18
Views: 1219

Re: Uncertainty in Speed [ENDORSED]

I think it goes like this:
(p)(x) = (1/2)(h/2)
(p) = m(v)
From here you can plug in (0.01)*(0.05 nm) for x and solve.
by andrewcj 2C
Sat Oct 05, 2019 12:52 pm
Forum: Properties of Light
Topic: Electrical Field
Replies: 1
Views: 18

Electrical Field

Can someone explain 1.3 to me? The question is as follows: Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The extent of the change in the el...
by andrewcj 2C
Wed Oct 02, 2019 12:10 am
Forum: Empirical & Molecular Formulas
Topic: Clarification on the Vitamin C Example
Replies: 6
Views: 75

Re: Clarification on the Vitamin C Example

My best guess would be that rounding caused the masses of the individual elements to be a little smaller than they really are, which creates a small discrepancy in the summed mass and the total mass. In real life, our instruments are not always perfect, and this might be trying to show that.
by andrewcj 2C
Wed Oct 02, 2019 12:06 am
Forum: Significant Figures
Topic: General Rules to Help with Sig Figs
Replies: 18
Views: 211

Re: General Rules to Help with Sig Figs

I really think 5293 has 4 sig figs, not 5. I think if it was 5293.0, it would have 5 sig figs.
by andrewcj 2C
Tue Oct 01, 2019 10:06 pm
Forum: Limiting Reactant Calculations
Topic: 2 Limiting Reactants
Replies: 9
Views: 64

Re: 2 Limiting Reactants

Suppose the activation energy is too high for the reaction to proceed without a catalyst. Does that make a difference?
by andrewcj 2C
Tue Oct 01, 2019 10:05 pm
Forum: Significant Figures
Topic: Rounding
Replies: 3
Views: 44

Rounding

When it comes to rounding when the digit after the last digit you keep is 5, how should we do it? I've learned to round down if the previous digit is even, and up if the previous digit is odd, but I'm not sure if that's standard convention. For example, if I only wanted 2 sig figs and the number in ...
by andrewcj 2C
Mon Sep 30, 2019 9:55 pm
Forum: Limiting Reactant Calculations
Topic: 2 Limiting Reactants
Replies: 9
Views: 64

Re: 2 Limiting Reactants

A little unrelated, but if there is a reaction that requires a catalyst, and the catalyst is present in very small quantities relative to the reactants, is it called a limiting reactant because it severely slows the reaction, or do we classify it as something else?

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