Search found 20 matches

by Daniel Zhang 1E
Fri Mar 11, 2016 10:34 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Why is heat of vaporization not considered in this problem?
Replies: 2
Views: 302

Re: Why is heat of vaporization not considered in this probl

Yes! Since it is required to boil it is just the amount of heat needed to get to boiling point. Vaporization would occur at anything above 100 degrees celsius the difference comes from the wording, if it had said vaporize we would use the enthalpy of vaporization but since it says to boil we can om...
by Daniel Zhang 1E
Fri Mar 11, 2016 1:45 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Why is heat of vaporization not considered in this problem?
Replies: 2
Views: 302

Why is heat of vaporization not considered in this problem?

In Q1A of the 2011 Final, it asks for us to calculate the amount of methane needed to combust to generate enough heat to boil 50.0mL of water. However, in the solutions it does not consider the amount of energy required to vaporize the water - it only considers the energy to raise the temperature to...
by Daniel Zhang 1E
Sun Mar 06, 2016 8:12 pm
Forum: *Alkynes
Topic: Naming
Replies: 3
Views: 861

Re: Naming

Keep in mind that triple bonds have priority for lowest numbering in alkynes
by Daniel Zhang 1E
Sun Mar 06, 2016 8:11 pm
Forum: *Cycloalkanes
Topic: Numbering Carbons
Replies: 3
Views: 435

Re: Numbering Carbons

Double and triple bonds have priority over substituents and should always be given the lowest possible number. For substituents, you give priority to them based on alphabetical order. Alphabetical order does not include any of the prefixes (di, tri, etc.) and it does not include the common prefixes...
by Daniel Zhang 1E
Sun Mar 06, 2016 8:05 pm
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: Cis and trans vs Z and E
Replies: 1
Views: 435

Cis and trans vs Z and E

How do we know when to use each classification? When do we know whether or not we should classify according to cis and trans or z and e?
by Daniel Zhang 1E
Wed Mar 02, 2016 2:52 pm
Forum: *Alkanes
Topic: Prioritizing in naming
Replies: 2
Views: 351

Prioritizing in naming

How come for 4-ethyl-2,2-dimethyl-hexane dimethyl is prioritized for lower numbering? Shouldn't ethyl be prioritized so that it would be 3-ethyl-5,5-dimethyl-hexane because ethyl is listed first in the name?
by Daniel Zhang 1E
Thu Feb 18, 2016 2:55 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equilibrium vs steady-state
Replies: 2
Views: 821

Pre-equilibrium vs steady-state

How do we know which of these two methods to use? Are there specific conditions we should look for or will the question tell us which of the two to use?
by Daniel Zhang 1E
Mon Feb 08, 2016 10:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: How to know what units for pressure to use?
Replies: 2
Views: 368

Re: How to know what units for pressure to use?

But the units don't cancel out? It's
by Daniel Zhang 1E
Mon Feb 08, 2016 10:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams and spectator ions
Replies: 1
Views: 339

Cell diagrams and spectator ions

Are we supposed to include spectator ions when we draw the cell diagrams in line notation? Online sources say that you shouldn't but the solution for 14.15 says that you should.
by Daniel Zhang 1E
Mon Feb 08, 2016 5:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: How to know what units for pressure to use?
Replies: 2
Views: 368

How to know what units for pressure to use?

For question 4 on the 2011 practice midterm, the answer was given in bar even though there was no indication of it being used in the constants provided. How do we know to use bar rather than kPa or atm?
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by Daniel Zhang 1E
Sun Feb 07, 2016 7:27 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: How to identify systems
Replies: 2
Views: 396

Re: How to identify systems

An isolated system is similar to a calorimeter with a lid. None of the matter inside will come out, and the calorimeter will contain any transfer of energy between the system and its surroundings. An closed system is like a lightbulb. It is sealed so that none of the components can come out but can ...
by Daniel Zhang 1E
Mon Jan 25, 2016 10:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Isothermal, reversible expansion at constant pressure
Replies: 1
Views: 211

Isothermal, reversible expansion at constant pressure

Which work equation should we use for problems with isothermal, reversible reactions at constant pressure? The course reader says to use for reversible expansions with constant pressure and for isothermal, reversible expansions with variable pressure.
by Daniel Zhang 1E
Sat Jan 23, 2016 4:49 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Standard entropy of vaporization of ammonia
Replies: 2
Views: 663

Re: Standard entropy of vaporization of ammonia

So would we assume that the pressure has decreased after the ammonia has become a gas?
by Daniel Zhang 1E
Thu Jan 21, 2016 10:51 am
Forum: Phase Changes & Related Calculations
Topic: Diatomic vs Monotomic Gases Clarification
Replies: 2
Views: 268

Re: Diatomic vs Monotomic Gases Clarification

Diatomic molecules will tend to have higher entropy due to this equation: S = k_{b}lnW The number of microstates (W) is given by the equation: W = m^{n} m is the number of states while n is the total number of particles. A diatomic molecule would have a greater number of microstates and, therefore, ...
by Daniel Zhang 1E
Thu Jan 21, 2016 10:42 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Standard entropy of vaporization of ammonia
Replies: 2
Views: 663

Standard entropy of vaporization of ammonia

Why is it that ammonia can remain in a gaseous state while below the temperature of vaporization? For question 9.20, we are supposed to calculate the standard entropy of vaporization of ammonia @210K. The temperature of vaporization of ammonia is 329.4K. To do the problem, we have to assume the liqu...
by Daniel Zhang 1E
Mon Jan 11, 2016 9:38 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Using ideal gas constants
Replies: 1
Views: 212

Using ideal gas constants

How do we know when or what gas constants to use when calculating for the change in internal energy of a gas with constant pressure? For example, 8.9 from the textbook uses 8.314 and 0.08206, but how did they know to use these constants?
by Daniel Zhang 1E
Mon Nov 23, 2015 12:31 am
Forum: Empirical & Molecular Formulas
Topic: Video: Empirical Formulas
Replies: 3
Views: 630

Video: Empirical Formulas

Here's my video on how to find the empirical formula of a compound. Contributors include: Anthony Giron, Carrie Huang, and Daniel Zhang.
by Daniel Zhang 1E
Sun Nov 08, 2015 8:42 pm
Forum: Lewis Structures
Topic: Formal charge vs octet rule
Replies: 2
Views: 550

Formal charge vs octet rule

Does the formal charge or the octet rule create a more stable Lewis structure for elements who can have expanded octets? For example, sulfur in SO _{2} can form a double bond with both oxygens to have a low formal charge. However, sulfur would have an expanded octet. If sulfur formed a double bond w...
by Daniel Zhang 1E
Tue Oct 13, 2015 8:34 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration for Tungsten (W)
Replies: 1
Views: 1825

Electron Configuration for Tungsten (W)

Why is the electron configuration for tungsten instead of ? Shouldn't the 6s orbital lend an electron to the 5d orbital for a more stable half-orbital?
This is based on the answer for 2.43 from the textbook, part e).
by Daniel Zhang 1E
Sun Oct 11, 2015 11:58 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg vs. Bohr equation for hydrogen atom
Replies: 1
Views: 2726

Re: Rydberg vs. Bohr equation for hydrogen atom

You can use both equations. If using the Rydberg you can use the frequency value to find E with

You can plug this into the Rydberg formula to figure out the principle quantum level the electron started from.

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