Search found 30 matches

by Vivien Ho 3L
Sat Feb 07, 2015 2:37 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculating The Energy Changes When Heating An Ideal Gas
Replies: 4
Views: 965

Re: Calculating The Energy Changes When Heating An Ideal Gas

Hi Jennifer, That was not the question I was asking, but thanks anyway! What I meant was why must the expansion process be broken down into two steps? (ie. heating at constant volume to the final temperature and allowing the gas to expand isothermally?) Why does the isothermal expansion in this ques...
by Vivien Ho 3L
Wed Feb 04, 2015 12:10 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Calculating The Energy Changes When Heating An Ideal Gas
Replies: 4
Views: 965

Calculating The Energy Changes When Heating An Ideal Gas

I do not really understand the concept in Example 7.6 in the textbook: Calculate the final temperature and the change in internal energy when 500.J of energy is transferred as heat to 0.900 mol O2(g) at 298K and 1.00 atm at (a) constant volume (b) constant pressure. Treat the gas as ideal. Why do th...
by Vivien Ho 3L
Fri Jan 30, 2015 11:21 am
Forum: Calculating Work of Expansion
Topic: Isothermal reversible expansion
Replies: 3
Views: 1909

Re: Isothermal reversible expansion

I did use w=-nRT ln (V2/V1).
So now I've got -(2.00mol)(8.314J/Kmol)(300K)ln (18.00L/6.00L)=-5.48kJ
As deltaU=0, q=-w =+5.48kJ

But it says the final pressure is 1.20 at when it's supposed to be 1atm which confuses me!
Is there a typo?
by Vivien Ho 3L
Fri Jan 30, 2015 10:37 am
Forum: Calculating Work of Expansion
Topic: Isothermal reversible expansion
Replies: 3
Views: 1909

Isothermal reversible expansion

I am confused how to answer this question as it has conflicting information: If 2.00 mol of an ideal gas at 300 K and 3.00 atm expands isothermally and reversibly from 6.00 L to 18.00 L and has a final pressure of 1.20 atm, what is w, q, and delta u? Why are there changes in both the pressure and vo...
by Vivien Ho 3L
Fri Jan 30, 2015 12:22 am
Forum: Calculating Work of Expansion
Topic: isothermal reversible expansion with V and P change
Replies: 8
Views: 1229

Re: isothermal reversible expansion with V and P change

When using U=3/2 nRT, how do we exactly find delta T? I'm rather confused about this step.
Aren't the moles and temperature constant in the process? How do we get delta T?
by Vivien Ho 3L
Sun Jan 25, 2015 12:01 pm
Forum: Calculating Work of Expansion
Topic: Self Test 7.2A Comparing Reversible and Irreversible Expansi
Replies: 1
Views: 266

Self Test 7.2A Comparing Reversible and Irreversible Expansi

For this question I calculated the irreversible work: w=-(5.00atm)×(-1.00L) =(5.00Latm)×(101.325J) =506.625 =0.51kJ and the reversible work: w=-(0.100mol)×(8.314J/Kmol)×(303K)×ln(1.00L/2.00L) =174.61J =0.17kJ which is smaller than the value of the irreversible compression. However, the reversible co...
by Vivien Ho 3L
Sun Jan 25, 2015 11:48 am
Forum: Calculating Work of Expansion
Topic: Sig Figs For Thermodynamic Problems?
Replies: 2
Views: 504

Sig Figs For Thermodynamic Problems?

If the question contains a number with two sig figs like 30C, does this mean that all answers have to be 2 sig figs even though "30C" is not used in the question? For Self Test 7.2B, I got -0.20kJ and -1.7kJ for my answers so they had two sig figs. However, the answers are -202J and and 1....
by Vivien Ho 3L
Sun Jan 11, 2015 3:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Are all combustions endothermic?
Replies: 2
Views: 4564

Re: Are all combustions endothermic?

You may be confused between the heat of the system and the heat of the surroundings. "Exothermic" and "endothermic" are used to describe the heat of a system. When combustion occurs, the heat of the surroundings INCREASES. This is due to the heat RELEASED from the system. The sys...
by Vivien Ho 3L
Sat Dec 13, 2014 5:39 pm
Forum: Photoelectric Effect
Topic: Video: 2014 Fall Midterm Q4
Replies: 1
Views: 350

Video: 2014 Fall Midterm Q4

A video of me working though Q4 from the 2014 Fall Quarter Midterm.
by Vivien Ho 3L
Sat Dec 13, 2014 4:26 pm
Forum: Significant Figures
Topic: Sig Figs in Titrant Volume
Replies: 2
Views: 352

Sig Figs in Titrant Volume

Let's say I've got a titrant volume of 25. To find the halfway volume, it would be 12.5 . If the answers have to have two sig figs, do I need to round it off to 12? (I think this would make the following calculations inaccurate.)
by Vivien Ho 3L
Mon Dec 08, 2014 11:11 pm
Forum: *Titrations & Titration Calculations
Topic: Reason for doing Titrations
Replies: 1
Views: 292

Reason for doing Titrations

So this is just to confirm that I'm getting this right or not. We do titrations to figure out the concentration of the sample. 1. We know the moles, volume and concentration of the titrant because we made it. 2. We find the volume of the sample by reading off the graph at the stoichiometric point an...
by Vivien Ho 3L
Thu Dec 04, 2014 7:25 pm
Forum: Naming
Topic: Writing the formula
Replies: 2
Views: 389

Writing the formula

I thought that we would need to write the ligands according to alphabetical order when writing the formula. However, I saw someone mention that Dr. Lavelle once said that the anions should be listed first then the neutral ions. So which is it? Can someone clarify this?
by Vivien Ho 3L
Thu Dec 04, 2014 7:22 pm
Forum: Naming
Topic: Naming [Co(en)2(CN)Cl]Cl
Replies: 5
Views: 1103

Re: Naming [Co(en)2(CN)Cl]Cl

Both chloro and chlorido can be used. Chloro is the old version of naming and chlorido is the new IUPAC name for it. Dr. Lavelle mentioned that both will be accepted but we would generally use chloro in this class.
by Vivien Ho 3L
Thu Dec 04, 2014 7:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Quiz 3 Preparation Fall 2013 Quiz: #10
Replies: 9
Views: 1352

Re: Quiz 3 Preparation Fall 2013 Quiz: #10

Hey Ellie, did you square the concentration of BrCl in your calculations? Coz if you didn't you would end up with 0.26 for your x value which would result in 0.54 + 2 (0.26) = 1.06 which becomes 1.1 after rounding off. Just a suggestion :)
by Vivien Ho 3L
Wed Dec 03, 2014 10:25 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Quiz 3 Prep #8
Replies: 1
Views: 1121

Quiz 3 Prep #8

Consider the following reaction: NH4HS (s) <->NH3 (g) + H2S (g)

If the value of Kp is 0.11atm^2 at 300K, calculate the equilibrium partial pressure of NH3 (g) starting from pure NH4HS(s).

I'm confused about how to solve this question. Help please?
by Vivien Ho 3L
Wed Dec 03, 2014 9:04 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Quiz 3 WB #10
Replies: 6
Views: 933

Re: Quiz 3 WB #10

When writing out the expressions for the new equilibrium concentrations, I was confused at first as it didn't really seem as it was following Le Chatelier's principle. However, I went ahead and used 0.54-2x as it is a reactant. After solving the problem, I saw that Le Chatlier's principle would kick...
by Vivien Ho 3L
Wed Dec 03, 2014 8:49 am
Forum: Naming
Topic: Chemical Formula
Replies: 4
Views: 542

Re: Chemical Formula

According to Toolbox 16.1 of the textbook, it says we have to write the chemical symbols of ligands in alphabetical order. Therefore, it should be Cl first then NH3.
by Vivien Ho 3L
Mon Nov 17, 2014 6:44 am
Forum: Naming
Topic: Ligands with Short Forms
Replies: 1
Views: 245

Ligands with Short Forms

When naming a complex with ligands like "en", "dien", "ox" or "edta" in it, Do we sort them based on alphabetical order or do we put them in front due to the number of bonds formed? Also, will we be ever required to write out the long form in the chemical form...
by Vivien Ho 3L
Mon Nov 17, 2014 6:36 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelating complexes (16.33 and 16.34)
Replies: 1
Views: 330

Re: Chelating complexes (16.33 and 16.34)

Hi! In class, it was mentioned that two atoms separated by two atoms in the middle (with a shape of \_/) is the most convenient structure for bidentate ligands. According to this, the answer for both 16.33 and 16.34 is (b). There may be other possible structures but I'm not sure about those. Hope th...
by Vivien Ho 3L
Wed Nov 05, 2014 8:38 am
Forum: Lewis Structures
Topic: Calculating Number of Electrons
Replies: 2
Views: 313

Calculating Number of Electrons

When drawing lewis structures, we add an electron for a negative charge. So, we should subtract an electron for a positive charge, right?
by Vivien Ho 3L
Wed Nov 05, 2014 8:17 am
Forum: Octet Exceptions
Topic: Q9 Fall 2013 Quiz 2
Replies: 2
Views: 1165

Q9 Fall 2013 Quiz 2

This is from Q9 in the Fall 2013 Quiz 2 Prep.
Which of the following species has two unpaired electrons?
A. OF+ B. NO+ C. CO+
I don't really understand this question. Does "two unpaired electrons" mean biradicals? Can someone please explain how to approach this question? Thanks!
by Vivien Ho 3L
Wed Nov 05, 2014 8:09 am
Forum: Ionic & Covalent Bonds
Topic: Ionic Character and Covalent Character
Replies: 4
Views: 1000

Re: Ionic Character and Covalent Character

Just to add, when covalent character occurs, electrons of the atom with lower electronegativity will be pulled towards the atom with higher electronegativity.
by Vivien Ho 3L
Mon Nov 03, 2014 6:32 pm
Forum: Octet Exceptions
Topic: Location of Unpaired Electron
Replies: 3
Views: 523

Re: Location of Unpaired Electron

Which one gets completed first will be the one with the highest electronegativity (electronaffinity or ionization energy). So if there should be a lone pair, it should go to the one with the least electronegativity (electronaffinity or ionization energy). I was actually asking about free radicals. ...
by Vivien Ho 3L
Mon Nov 03, 2014 3:59 am
Forum: Octet Exceptions
Topic: Location of Unpaired Electron
Replies: 3
Views: 523

Location of Unpaired Electron

When drawing Lewis structures, where should I put the unpaired electron? Is there a rule for this?
by Vivien Ho 3L
Mon Nov 03, 2014 3:27 am
Forum: Resonance Structures
Topic: Number of Resonance Structures
Replies: 1
Views: 261

Number of Resonance Structures

How many resonance structures can there be for a particular structure? Should we only consider the variations of structures with the best formal charge or all possible structures that conform to the correct number of electrons and the octet rule?
by Vivien Ho 3L
Fri Oct 31, 2014 2:40 pm
Forum: Coordinate Covalent Bonds
Topic: Lewis Acid or Double Bond?
Replies: 3
Views: 1002

Re: Lewis Acid or Double Bond?

Oh I see. I tried using formal charge to see which is the best structure for the nitrate ion NO3 and it shows that for the double bond NO3, the single bond Os have an FC of -1 , the double bond oxygen has an FC of 0 and N has an FC of +1. However if N were to have 6 valence electrons it would result...
by Vivien Ho 3L
Mon Oct 27, 2014 9:41 pm
Forum: Coordinate Covalent Bonds
Topic: Lewis Acid or Double Bond?
Replies: 3
Views: 1002

Lewis Acid or Double Bond?

In the course reader, it says boron trifluoride has only 6 valence electrons. It completes its octet if it forms a coordinate covalent bond with another atom. Why can't it complete its octet by having 8 valence electrons then share its electrons to have one double bond? On the other hand, the nitrat...
by Vivien Ho 3L
Mon Oct 27, 2014 9:38 pm
Forum: Ionic & Covalent Bonds
Topic: Resonance Structure
Replies: 3
Views: 449

Re: Resonance Structure

Resonance is a blending of the structures that we have drawn. None of the lewis structures that we draw is the real structure. The lewis structures that we draw do not change quickly from one to another either. The actual structure is an average of the resonance structures so that more stable bonds ...
by Vivien Ho 3L
Sun Oct 12, 2014 6:19 pm
Forum: Properties of Light
Topic: Diffraction and Incident Light
Replies: 6
Views: 714

Re: Diffraction and Incident Light

Hi. I'm not really sure if what I say here is correct or not, but it helps me grasp the idea of why the waves are circular. I think that the shape of the waves depends on the size of the slit. Imagine a small slit, the waves would have to 'squeeze' through the slit so they become very circular. On t...
by Vivien Ho 3L
Sun Oct 12, 2014 5:54 pm
Forum: Properties of Electrons
Topic: Atoms/ Molecules
Replies: 2
Views: 416

Re: Atoms/ Molecules

Hi there!

Atoms in a molecule are held together by covalent bonds. Covalent bonds occur when atoms share electrons with each other.

Hope this answers your question.

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