Search found 13 matches

by Jennifer Cheng 2L
Sun Jan 17, 2016 9:00 pm
Forum: Phase Changes & Related Calculations
Topic: Isolated Systems
Replies: 2
Views: 389

Re: Isolated Systems

In an isolated system, nothing is exchanged between the system and the surroundings. So nothing gets in and nothing gets out, including matter and energy. If energy can't get in or out, that means it stays constant.
by Jennifer Cheng 2L
Sun Jan 10, 2016 11:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When to use each method
Replies: 3
Views: 438

Re: When to use each method

For further clarification, is it just the given information and enthalpy values that determine which method will prove to be the most efficient when solving? Yes, you determine which method to use by looking at the given information. For instance, if you are given bond enthalpies, you cannot use He...
by Jennifer Cheng 2L
Sun Dec 06, 2015 12:42 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: M.O. Theory and oxygen
Replies: 2
Views: 485

Re: M.O. Theory and oxygen

Yes you would use the Z ≥ 8 diagram since oxygen has an effective nuclear charge equal to 8.
by Jennifer Cheng 2L
Wed Nov 25, 2015 2:32 pm
Forum: Polyprotic Acids & Bases
Topic: Acidity of HClO and HClO4
Replies: 1
Views: 784

Re: Acidity of HClO and HClO4

Perchloric acid has more electronegative oxygen atoms which pull the electron density off the chlorine atom. This pulling power (electron induction) stabilizes the molecule. This makes the anion stable, which makes it a stronger acid. If the anion is stable, it won't want to attract any H+ atoms bec...
by Jennifer Cheng 2L
Wed Nov 18, 2015 11:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Finding what K equals, given only Q
Replies: 1
Views: 297

Re: Finding what K equals, given only Q

Professor Lavelle said to skip this problem in the homework because it requires topics/equations that we have not learned before.
by Jennifer Cheng 2L
Sat Nov 14, 2015 4:52 pm
Forum: Ideal Gases
Topic: Exothermic and Endothermic Reactions
Replies: 3
Views: 893

Re: Exothermic and Endothermic Reactions

You can also think of it like this:

Endothermic reactions: Reactants + Heat → Products
Since you are adding heat, there is a positive change.

Exothermic reactions: Reactants → Products + Heat
Heat is released, or "subtracted" from the reactants, so there is a negative change.
by Jennifer Cheng 2L
Sun Nov 08, 2015 3:25 pm
Forum: Naming
Topic: Naming and Order
Replies: 3
Views: 396

Naming and Order

If the initial question asks for the formula of a pentaaquahydroxonickel(III) ion, does it matter if we write it as [Ni(OH)(OH2)5]2+ or as [Ni(OH2)5(OH)]2+?

Also, would the water molecule be written as H2O or OH2 in each case?
by Jennifer Cheng 2L
Sat Nov 07, 2015 11:39 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Difference between Q and K
Replies: 3
Views: 680

Re: Difference between Q and K

You do calculations for Q with the initial molar concentrations given. Comparing it to K, the equilibrium constant, tells you which way the reaction is going, either forward or backward. If Q equals K, that means that the reaction is at equilibrium.
by Jennifer Cheng 2L
Wed Oct 28, 2015 4:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T-shaped vs. Trigonal Pyramidal
Replies: 2
Views: 1865

Re: T-shaped vs. Trigonal Pyramidal

A molecule is t-shaped if it has 5 areas of electron density, 3 of which are bonded pairs and 2 of which are lone pairs (AX 3 E 2 ). Think about the parent function: AX 5 . It has one plane with three bonded atoms that form a triangle shape and then two bonded atoms sticking up and down perpendicula...
by Jennifer Cheng 2L
Mon Oct 19, 2015 9:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw and Triganol Bipyramid
Replies: 4
Views: 2181

Re: Seesaw and Triganol Bipyramid

The trigonal pyramidal structure actually has four areas of electron density. Take SO 3 2- for example. The sulfur atom is connected to three oxygen atoms (3 areas of electron density) and then it has a lone pair (1 area of electron density). So that gives it a total of four areas of electron densit...
by Jennifer Cheng 2L
Tue Oct 13, 2015 11:25 am
Forum: Resonance Structures
Topic: Bond Angle
Replies: 2
Views: 433

Re: Bond Angle

It doesn't really matter as of now. Just place the atoms symmetrically around the central atom. Later on when you learn about VESPR models (the video above this post) you will find that there are certain bond angles for certain structures.
by Jennifer Cheng 2L
Wed Oct 07, 2015 4:34 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations in the d Orbital
Replies: 2
Views: 464

Electron Configurations in the d Orbital

In the Fall 2015 Chem 14A course reader, there's a statement on page 22 that says: Two exceptions: Half full d 5 and full d 10 subshell have lower energy. I don't think Professor Lavelle really talked about this during the lecture, so could someone explain what this means? I'm confused about what th...
by Jennifer Cheng 2L
Tue Sep 29, 2015 3:47 pm
Forum: Empirical & Molecular Formulas
Topic: Molecular Formulas
Replies: 3
Views: 837

Re: Molecular Formulas

Not sure about this, but you could convert to percentages and then use the amount of grams of each element you would find in an 100g sample, but then you would have to convert to moles again afterwards anyways. I think it's just easier to go straight from grams to moles directly.

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