Search found 52 matches

by Cristina Sarmiento 1E
Sun Mar 18, 2018 10:04 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Spontaneity in a cell reaction
Replies: 4
Views: 269

Re: Spontaneity in a cell reaction

Based on the equation Matt gave, if Ecell is positive, Delta G is negative = spontaneous. If Ecell is negative, Delta G is positive = nonspontaneous.
by Cristina Sarmiento 1E
Sun Mar 18, 2018 9:46 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt electrode
Replies: 2
Views: 215

Re: Pt electrode

You also add Pt when there is a solid that cannot conduct electricity (e.g. halogen)
by Cristina Sarmiento 1E
Fri Mar 16, 2018 10:20 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question from test 1
Replies: 1
Views: 211

Re: Question from test 1

a. Yes, there is a phase change occurring because liquefied propane was released as gaseous propane vapors.
b. Yes, the temperature remained constant, meaning the surroundings had to supplement heat to keep the temperature from changing.
by Cristina Sarmiento 1E
Fri Mar 16, 2018 10:16 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Midterm question 6a
Replies: 5
Views: 329

Re: Midterm question 6a

They were both correct because complex molecules have more entropy than less complex molecules and gas has more entropy than liquid.
by Cristina Sarmiento 1E
Fri Mar 16, 2018 10:14 pm
Forum: *Nucleophiles
Topic: nucleophile?
Replies: 4
Views: 354

Re: nucleophile?

The nucleophile attacks a positively charged, for example carbon, and in the process, substitutes with the leaving group.
by Cristina Sarmiento 1E
Fri Mar 16, 2018 10:01 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: sign of k
Replies: 3
Views: 418

Re: sign of k

No, rate constants can never be negative.
by Cristina Sarmiento 1E
Fri Mar 16, 2018 5:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 question 4
Replies: 4
Views: 132

Re: Test #2 question 4

When you flip the sign because you flip the equation, you must do Ecell = Ecathode + Eanode.
It is also helpful to know that for galvanic cells, the Ecell must always be positive.
by Cristina Sarmiento 1E
Thu Mar 15, 2018 3:39 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Coefficients in Rate Law
Replies: 2
Views: 115

Re: Coefficients in Rate Law

Just adding on that with reaction mechanisms, the rate law will sometimes have the same exponents as the coefficients in the chemical equation by mere coincidence. We cannot assume that the coefficients will be the exponents. We must look at the elementary steps.
by Cristina Sarmiento 1E
Thu Mar 15, 2018 1:29 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: catalysts
Replies: 5
Views: 207

Re: catalysts

Catalysts can be appear in the overall rate law, but sometimes they are cancelled out (e.g. consumed in the fast step before and produced in the slow step) and therefore would not appear in the rate law.
by Cristina Sarmiento 1E
Thu Mar 15, 2018 1:26 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which equilibrium equation to use
Replies: 2
Views: 109

Re: Which equilibrium equation to use

If a fast step is before a slow step, we can assume the fast step is in equilibrium. I believe Lavelle called it pseudo equilibrium.
We substitute equilibrium constant K to get rid of any intermediates because intermediates cannot be in the rate law.
by Cristina Sarmiento 1E
Thu Mar 15, 2018 1:13 pm
Forum: General Rate Laws
Topic: Test #3 Q5
Replies: 3
Views: 130

Re: Test #3 Q5

Since both reactants are first order, the rate law would be rate law = k[CHCL3][CL2]. Because you are given the instantaneous rate of reaction, 2.54 x 10^/2 mol/L and the concentrations can be solved for, you just plug those numbers into the rate law equation to find k. To find the concentration of ...
by Cristina Sarmiento 1E
Tue Mar 06, 2018 10:18 pm
Forum: General Rate Laws
Topic: 15.5
Replies: 3
Views: 130

Re: 15.5

Someone please correct me if I am wrong, but do we multiply the unique average rate by the coefficients (for e.g. oxygen) to find its rate because the unique average rate already took into account its coefficients and now we just have to multiply it back?
by Cristina Sarmiento 1E
Tue Mar 06, 2018 10:14 pm
Forum: General Rate Laws
Topic: 15.5
Replies: 3
Views: 130

Re: 15.5

I thought the unique average rate law took into account the stoichiometric coefficients so it's not necessarily just one mole
by Cristina Sarmiento 1E
Tue Mar 06, 2018 10:06 pm
Forum: First Order Reactions
Topic: 15.23 c
Replies: 1
Views: 107

Re: 15.23 c

The equation given is 2A --> B + C So there is a decrease in A because it is making B (an increase in B) If we know the increase in B, we can use the coefficients from the equation to convert moles of B back to moles of A. The number we get from the conversion is how much A was used to make B. So if...
by Cristina Sarmiento 1E
Tue Mar 06, 2018 10:00 pm
Forum: General Rate Laws
Topic: Proper units
Replies: 7
Views: 229

Re: Proper units

The textbook tends to write the answers in moles
by Cristina Sarmiento 1E
Tue Mar 06, 2018 9:55 pm
Forum: General Rate Laws
Topic: 15.5
Replies: 3
Views: 130

15.5

Why do we multiply the unique rate by the coefficient of oxygen to find its rate and multiply the unique rate by the coefficient of water to find its rate? Why don't we divide the unique rate by the coefficient?
by Cristina Sarmiento 1E
Wed Feb 28, 2018 4:32 pm
Forum: General Rate Laws
Topic: Negative 1/a
Replies: 8
Views: 290

Re: Negative 1/a

Because the reactant is being consumed, the overall concentration of the reactant is decreasing so there is a negative rate of change. However, if the question asked at what rate was A being consumed, then it will be a positive answer. Just be careful about how the question is worded! Can you pleas...
by Cristina Sarmiento 1E
Wed Feb 28, 2018 4:23 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 3
Replies: 6
Views: 289

Re: Test 3

Yes, it only goes to #39
by Cristina Sarmiento 1E
Wed Feb 28, 2018 4:20 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Textbook Problems 15.3 and 15.5
Replies: 7
Views: 497

Re: Textbook Problems 15.3 and 15.5

So when you are calculating the rate of reaction that is not the unique rate of reaction, you multiply the concentration by the coefficient?
by Cristina Sarmiento 1E
Wed Feb 28, 2018 4:16 pm
Forum: General Rate Laws
Topic: 15.3 C
Replies: 8
Views: 465

Re: 15.3 C

The unique reaction rate takes into account the coefficients of the chemical equation.
by Cristina Sarmiento 1E
Wed Feb 28, 2018 4:12 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.3 c
Replies: 2
Views: 91

Re: 15.3 c

The unique rate of reaction is the general rate of (for example)
when
This rate of reaction takes into account the coefficients of the reaction.
by Cristina Sarmiento 1E
Tue Feb 27, 2018 10:51 pm
Forum: General Rate Laws
Topic: 15. 17 [ENDORSED]
Replies: 2
Views: 103

15. 17 [ENDORSED]

How do you know when a reactant is independent of the rate?
by Cristina Sarmiento 1E
Thu Feb 22, 2018 7:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Order for Same Phases
Replies: 4
Views: 198

Re: Cell Diagram Order for Same Phases

I put it in order of the reactants, products
I am not sure if this is completely right but I have gotten the same answers so far
by Cristina Sarmiento 1E
Wed Feb 21, 2018 12:45 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Oxidizing vs. Reducing agent
Replies: 1
Views: 78

Re: Oxidizing vs. Reducing agent

The oxidizing agent is the substance being reduced.
The reducing agent is the substance being oxidized.

When the cell potential is more positive, it has a stronger oxidizing agent
When the cell potential is more negative, it has a stronger reducing agent
by Cristina Sarmiento 1E
Wed Feb 21, 2018 12:34 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 3
Views: 95

Re: Cell Diagrams

The commas mean that they are in the same phase.
" | " means that they are in different phases
"||" is the salt bridge that separates the anode from the cathode
by Cristina Sarmiento 1E
Tue Feb 20, 2018 6:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+
Replies: 2
Views: 115

Re: H+

When you need to balance out the oxygens, you add H20 to other side. Then to balance the H's from the H20, you add H+ to the side of the oxygens so everything balances out.
by Cristina Sarmiento 1E
Tue Feb 20, 2018 6:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Structure
Replies: 3
Views: 83

Re: Cell Diagram Structure

You use one | to represent different phases in contact with each other and two || to indicate the salt bridge.
by Cristina Sarmiento 1E
Tue Feb 20, 2018 6:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 2
Views: 85

Re: Cell Diagram

I think we use Pt when they are no other solids to transfer electrons.
by Cristina Sarmiento 1E
Wed Feb 14, 2018 11:55 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Temperature Relation
Replies: 2
Views: 102

Temperature Relation

Can someone please explain the relationship between temperature and internal energy ?
Also, the relationship between temperature and entropy?
Thanks
by Cristina Sarmiento 1E
Tue Feb 13, 2018 11:01 pm
Forum: Calculating Work of Expansion
Topic: Formulas for monatomic vs diatomic gases
Replies: 2
Views: 170

Formulas for monatomic vs diatomic gases

What formulas do you use when it is a) monatomic gas b) diatomic gas?
by Cristina Sarmiento 1E
Tue Feb 13, 2018 4:52 pm
Forum: Van't Hoff Equation
Topic: Vant Hoff Equation
Replies: 1
Views: 176

Vant Hoff Equation

How would you use the Vant Hoff Equation when there are two different temperatures given?
Do you solve for one temperature first and then the other and add them?
by Cristina Sarmiento 1E
Tue Feb 13, 2018 3:53 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta H at constant pressure
Replies: 2
Views: 97

Re: Delta H at constant pressure

At constant pressure delta H = q, which means q would have to be 0.
q is 0 when it is an adiabatic reaction.
by Cristina Sarmiento 1E
Tue Feb 13, 2018 3:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Constant Volume
Replies: 2
Views: 70

Re: Constant Volume

When w = 0, delta U = q.
q is only equal to delta H when it is q is at constant pressure.
by Cristina Sarmiento 1E
Sat Feb 10, 2018 9:55 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Entropy
Replies: 7
Views: 211

Re: Entropy

S°m is molar entropy.
S°f is standard entropy of formation.
S°r is standard reaction entropy.
by Cristina Sarmiento 1E
Sat Feb 10, 2018 9:51 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Exothermic/Endothermic [ENDORSED]
Replies: 3
Views: 157

Re: Exothermic/Endothermic [ENDORSED]

I think of catabolic reactions breaking down things, releasing energy = exothermic and anabolic reactions forming things, requiring energy = endothermic.
These reactions tend to go hand in hand with catabolic reactions supplying the energy for anabolic reactions.
by Cristina Sarmiento 1E
Thu Feb 08, 2018 8:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 9
Views: 374

Re: Spontaneity

Negative delta G means the reaction is spontaneous.
by Cristina Sarmiento 1E
Sat Feb 03, 2018 2:00 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Adiabatic [ENDORSED]
Replies: 4
Views: 187

Re: Adiabatic [ENDORSED]

When a reaction is adiabatic, q=0
by Cristina Sarmiento 1E
Sat Feb 03, 2018 1:57 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 3b on the test
Replies: 4
Views: 196

Re: Question 3b on the test

The isothermal reaction tells us that internal energy is equal to 0, which means q = -w. Since the temperature stayed constant while there was work being done, we know that there was a heat transfer from the surroundings into the system to maintain the temperature.
by Cristina Sarmiento 1E
Sat Feb 03, 2018 1:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: What does it mean for a reaction to be "thermodynamically favored?"
Replies: 6
Views: 3099

Re: What does it mean for a reaction to be "thermodynamically favored?"

Reactions that do not require energy are seen as more favorable. Since exothermic reactions release energy and endothermic reactions require energy, exothermic reactions are more favorable.
by Cristina Sarmiento 1E
Thu Jan 25, 2018 9:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Internal Energy
Replies: 5
Views: 187

Re: Internal Energy

If it was delta P instead of P in the equation, then pressure would equal 0 when it is constant.
by Cristina Sarmiento 1E
Thu Jan 25, 2018 9:47 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: DeltaU and DeltaH
Replies: 4
Views: 207

Re: DeltaU and DeltaH

Delta U = Delta H when there is constant pressure and constant volume. Remember that Delta U = q +w. Delta H = q when there is constant pressure. w= -P Delta V. So when volume is constant, Delta V = 0. Therefore when there is constant pressure and volume, you can substitute q & w and get delta U...
by Cristina Sarmiento 1E
Tue Jan 23, 2018 10:28 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes Equations
Replies: 4
Views: 189

Phase Changes Equations

Delta H fusion = Hm (liquid) - Hm (solid) as mentioned in the book and in lecture. What does Hm stand for? Are we going to have to know how to solve for delta H fusion or for the other delta H phase changes?
by Cristina Sarmiento 1E
Tue Jan 23, 2018 9:05 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes and Energy
Replies: 2
Views: 110

Re: Phase Changes and Energy

Melting, vaporization, and sublimation all require energy (endothermic).

Condensation releases energy.
by Cristina Sarmiento 1E
Tue Jan 23, 2018 9:01 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units
Replies: 2
Views: 76

Re: Units

I would just look at the units in your equation that you are trying to solve and see if the moles cancel out. If not, then delta H is kJ/mol. If the moles cancel out, then delta H is kJ.
by Cristina Sarmiento 1E
Tue Jan 23, 2018 8:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exothermic
Replies: 7
Views: 188

Re: Exothermic

An exothermic reaction releases energy, which means that heat is also being released, causing a rise of temperature.
by Cristina Sarmiento 1E
Fri Jan 19, 2018 2:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45 question
Replies: 4
Views: 127

Re: 8.45 question

I am also confused because in my notes I have that endothermic reactions absorbs and requires energy so breaking bonds would be endothermic. Exothermic releases and in my notes I put forming bonds would be exothermic but why would you release energy when you form bonds?
by Cristina Sarmiento 1E
Fri Jan 19, 2018 2:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework 87
Replies: 2
Views: 83

Re: Homework 87

When a reaction is endothermic, delta H is positive. Reactions that are endothermic include vaporization, melting/fusion,and sublimation because heat is being absorbed. When a reaction is exothermic, delta H is negative. A reaction that exothermic is combustion because heat is released.
by Cristina Sarmiento 1E
Fri Jan 19, 2018 2:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter vs. Bomb Calorimeter
Replies: 2
Views: 115

Re: Calorimeter vs. Bomb Calorimeter

A normal calorimeter is for constant pressure and a bomb calorimeter is for constant volume.
by Cristina Sarmiento 1E
Sun Jan 14, 2018 5:57 pm
Forum: Phase Changes & Related Calculations
Topic: Isolated vs Closed Systems
Replies: 2
Views: 95

Re: Isolated vs Closed Systems

An isolated system does not come in contact with its surroundings (heat stays in thermos).
A closed system has a fixed amount of matter and can exchange energy with its surroundings (the ice pack is used on injuries to exchange energy).
by Cristina Sarmiento 1E
Sun Jan 14, 2018 3:56 pm
Forum: Phase Changes & Related Calculations
Topic: Steam Burning
Replies: 7
Views: 279

Re: Steam Burning

Steam burns more because of the phase change from liquid to vapor. Water boils at 100 degrees Celsius and during the phase change of vaporization, heat continues to increase. So when the boiling water has been turned into steam, a lot more heat had been supplied and is the reason why steam burns more.
by Cristina Sarmiento 1E
Wed Jan 10, 2018 7:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity vs. Specific Heat Capacity
Replies: 6
Views: 204

Re: Heat Capacity vs. Specific Heat Capacity

Heat capacity is the amount of heat over how much the temperature increased; it's a ratio. Whereas specific heat capacity is the heat capacity divided by the mass of the sample. Molar heat capacity is similar to specific heat capacity but instead of dividing the heat capacity by the mass, you're div...

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