Search found 21 matches

by Anna Li 2E
Sun Mar 04, 2018 10:44 pm
Forum: General Rate Laws
Topic: Naming Clarification
Replies: 3
Views: 140

Re: Naming Clarification

If you've taken calculus you can remember that they are the same by thinking that when you find the derivative of something (ie: concentration vs. time) you are finding the slope of that graph. The 'instantaneous rate' can also be thought of the slope/tangent line of a graph at a specific point, som...
by Anna Li 2E
Sun Mar 04, 2018 10:28 pm
Forum: General Rate Laws
Topic: a value
Replies: 3
Views: 152

Re: a value

Going with what Max said, an example of this would be for the balanced equation 2H2+O2 --> 2H2O the 'a' value for for hydrogen for this example would be 2.
by Anna Li 2E
Sun Mar 04, 2018 9:52 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7606
Views: 1019242

Re: Post All Chemistry Jokes Here

What element is a girl's future best friend?
Carbon.
by Anna Li 2E
Sun Feb 25, 2018 10:15 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell potential calculation
Replies: 4
Views: 152

Re: Cell potential calculation

Galvanic cells generate electrical energy from spontaneous redox reactions, meaning that the deltaG (gibb's free energy) should be negative as we know that indicates spontaneous reactions. When reactions are spontaneous that means that E MUST be positive. So when you are adding/subtracting cell pote...
by Anna Li 2E
Sun Feb 25, 2018 10:10 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell Potential
Replies: 4
Views: 163

Re: Cell Potential

In actuality Hydrogen's absolute electrode potential isn't ACTUALLY 0, however it is set to 0 in order to create a basis of comparison with other redox reactions. This creates a reference point for other redox reactions which makes it easier to measure and discuss these reactions.
by Anna Li 2E
Sun Feb 25, 2018 4:59 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7606
Views: 1019242

Re: Post All Chemistry Jokes Here

A neutron walked into a bar and asked how much for a drink. The bartender replied, "for you, no charge."
by Anna Li 2E
Sun Feb 18, 2018 10:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: galvanic vs electrolytic
Replies: 4
Views: 109

Re: galvanic vs electrolytic

According to the textbook a galvanic cell is used to produce electricity while an electrolytic cell uses an electrical current to cause a chemical change however they both are electrochemical cells which is defined as “a system consisting of two electrodes in contact with an electrolyte.”
by Anna Li 2E
Sun Feb 18, 2018 10:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells
Replies: 2
Views: 97

Re: Galvanic cells

You can add more cathodes or anodes in a real life reaction by splitting a cathode/anode however I don't believe we would be tested on this in this course as it's not a concept that adds anything to the material.
by Anna Li 2E
Sun Feb 18, 2018 10:27 pm
Forum: Balancing Redox Reactions
Topic: Half reaction
Replies: 2
Views: 88

Re: Half reaction

E is in intrinsic property meaning that the value is independent on the size of the sample, or in this case the coefficients of the balanced equation. Unlike with Enthalpy where the deltaH of a reaction gets altered when you manipulate an equation (ie: when you manipulate reactions when using Hess's...
by Anna Li 2E
Sun Feb 11, 2018 10:30 pm
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: 9.25
Replies: 1
Views: 150

9.25

I understand that when drawing the lewis structure of SO2F2 it results in 6 unique different combinations, however I'm a little confused when thinking of this molecule in a 3 dimensional space. I assume that since the question is stating that SO2F2 adopts a positionally disordered arrangement that p...
by Anna Li 2E
Sun Feb 11, 2018 10:05 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Finding Temperature Where Reaction is Spontaneous
Replies: 2
Views: 109

Re: Finding Temperature Where Reaction is Spontaneous

You can also think about it like hypothetically what if we did set deltaG to a negative number? For example, you set deltaG=-1 and find the T value, you could set deltaG to an even smaller negative number, (ie -0.000001) and get a different temperature value. And so forth and so forth, always using ...
by Anna Li 2E
Sun Feb 11, 2018 9:50 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Why is deltaG of formation 0 for diatomic molecules?
Replies: 3
Views: 3024

Re: Why is deltaG of formation 0 for diatomic molecules?

The heat of formation is 0 only for certain diatomic molecules. This occurs for the elements where their natural/most common state is a diatomic. These elements are H2, N2, F2, O2, L2, Cl2, Br2. This is due to the fact that standard enthalpy of formation is defined as enthalpy change of a substance ...
by Anna Li 2E
Sun Feb 04, 2018 10:09 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: deltaS question
Replies: 7
Views: 266

Re: deltaS question

Also when solving equations that involve ideal gases, Cp is used for constant pressure and Cv is used for constant volume. Usually it is specified in the problem whether the ideal gas is under constant pressure/volume so substitute Cp or Cv accordingly.
by Anna Li 2E
Sun Feb 04, 2018 9:44 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Exercise 9.63
Replies: 2
Views: 144

Re: Exercise 9.63

I'm guessing you use Appendix A to check each molecule's gibb's free energy to see which ones have a positive free energy. Positive free energy corresponds with unstable molecules. This topic was also answered by Chem_Mod at this thread if you are still confused: https://lavelle.chem.ucla.edu/forum/...
by Anna Li 2E
Sun Feb 04, 2018 8:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy -/+
Replies: 4
Views: 146

Re: Gibbs Free Energy -/+

For Michael Cheng, when Gibbs Free Energy is negative it is associated with a spontaneous reaction. When gibbs is negative, the system is releasing energy (exergonic), and the definition of spontaneous is when a reaction proceeds without any outside force.
by Anna Li 2E
Sun Jan 28, 2018 10:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57 Hess's Law [ENDORSED]
Replies: 3
Views: 376

Re: 8.57 Hess's Law [ENDORSED]

For the equation in 8.57 all of the compounds combusts into CO2+H2O, so the equation becomes (delta H)= (Hc C2H2) +2(Hc H2) -(Hc C2H6). Here we use Hess’s Law to determine the entire reaction enthalpy so it would be (-1300 kJ/mol)+2(-286 kJ/mol)-(-1560 kJ/mol) which results in the answer -312 kJ/mol
by Anna Li 2E
Sun Jan 28, 2018 10:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Different Changes in Enthalpy symbols -ΔH
Replies: 3
Views: 239

Re: Different Changes in Enthalpy symbols -ΔH

ΔHc=enthalpy of combustion. This is when one mol of a compound is burned completely in oxygen.
ΔHL=lattice enthalpy of formation. An example of this would be how the gaseous form of Na+ and Cl- come together to create NaCl solid.
ΔHb=bond enthalpy which is the energy released when bonds are made.
by Anna Li 2E
Sun Jan 28, 2018 9:21 pm
Forum: Calculating Work of Expansion
Topic: In which situation does delta U=0 and that q=-w
Replies: 4
Views: 156

Re: In which situation does delta U=0 and that q=-w

U stands for internal energy, so when delta U (the change in internal energy) is zero, that indicates that reaction is isothermal, a.k.a there is no change in temperature. This occurs when q, (also known as heat added to the system) is equal to -w. You can view this -w as the system expanding of its...
by Anna Li 2E
Sun Jan 21, 2018 10:11 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: calculating specific heat
Replies: 5
Views: 242

Re: calculating specific heat

The equation for specific heat is Specific Heat Capacity= (n x ∆T)/q. Through this equation we can see that the heat capacity is determined by mols (n) and not volume. However, (although I don't know the specific question you are referencing) problems will sometimes give you volume(Liters) and press...
by Anna Li 2E
Sun Jan 21, 2018 9:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Is a bomb calorimeter an isolated system and is a coffee cup calorimeter a closed system?
Replies: 2
Views: 2256

Re: Is a bomb calorimeter an isolated system and is a coffee cup calorimeter a closed system?

The purpose of a bomb calorimeter is to calculate heat generated by a reaction (hence the name 'bomb') by measuring the difference in temperature of the water surrounding said reaction. So, if the bomb calorimeter was an isolated system, this heat transfer would be unable to occur and we would not b...
by Anna Li 2E
Sun Jan 21, 2018 9:06 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated vs Closed system
Replies: 3
Views: 226

Re: Isolated vs Closed system

It may be easier to picture an isolated system as a really high quality thermos where the substance inside and any heat inside cannot leave/interact with the surroundings. On the other hand, a closed system is like a sealed glass jar, where the substance inside stays the same, but heat can escape or...

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