## Search found 24 matches

Thu Mar 10, 2016 4:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Why does entrooy if the universe is deltag is negative?
Replies: 2
Views: 485

### Re: Why does entrooy if the universe is deltag is negative?

If deltaG is negative, then the reaction is spontaneous, and all spontaneous reactions have a positive deltaS(univ) value, because spontaneous reactions increase the entropy of the universe.
Thu Mar 10, 2016 4:45 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Calculating residual entropy
Replies: 3
Views: 1112

### Re: Calculating residual entropy

NO can be oriented as both NO and ON; BF3, no matter how you rotate the molecule, will look the same, because the F's are symmetric around the B. Therefore, NO has higher residual entropy, because it takes upon more orientations.
Thu Mar 10, 2016 4:34 pm
Forum: Phase Changes & Related Calculations
Topic: Phase of water as a product in combustion reaction?
Replies: 2
Views: 1550

### Re: Phase of water as a product in combustion reaction?

H2O is in the liquid, rather than gas, phase, because you're told that the reaction is occurring at room temperature (25 degrees Celsius).
Thu Mar 10, 2016 4:28 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Thermodynamic Systems(Open, closed, and isolated)
Replies: 2
Views: 757

### Re: Thermodynamic Systems(Open, closed, and isolated)

Yes, the entire universe would be considered an isolated system, as it has no "surroundings" with which to exchange matter or energy.
Thu Mar 10, 2016 4:21 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: midterm question of internal energy
Replies: 2
Views: 410

### Re: midterm question of internal energy

Note that this is only true for an ideal gas, because only ideal gases have no intermolecular forces, so the gas retains the same total potential energy, and thus the change in internal energy is 0 J.
Mon Feb 08, 2016 7:01 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: Molar entropy
Replies: 1
Views: 460

### Re: Molar entropy

Larger molecules have higher entropy, because they can occupy more orientations in space. Because the F atom is bigger than the H atom, the more F atoms you add, the higher the entropy.
Mon Feb 08, 2016 6:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Winter 2012 Midterm Question 6- free energy of combustion
Replies: 1
Views: 358

### Re: Winter 2012 Midterm Question 6- free energy of combustio

If you look to question 5A on the Winter 2013 midterm, it's pretty much exactly the same question as the one from the Winter 2012 midterm, and here it is noted that if you balanced the equation with whole number coefficients for every molecule, and ended up with a Gibbs free energy that was double t...
Mon Feb 08, 2016 6:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 2011 Midterm Q5B
Replies: 1
Views: 348

### Re: 2011 Midterm Q5B

It might be because it is given that the free energy is for 1 mol of glucose. Therefore, -2808 kJ/mol * 1 mol = -2808 kJ for the value of delta H for the reaction.
Mon Feb 08, 2016 6:29 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: log(Q) vs. ln(Q) in the nernst equation
Replies: 3
Views: 1026

### Re: log(Q) vs. ln(Q) in the nernst equation

Furthermore, when you use the ln(Q) version of the equation, you need to know temperature; on some of the practice midterm questions, this information was not provided. Using the log(Q) version of the equation, the only additional information required is the standard cell potential and number of mol...
Mon Feb 08, 2016 6:24 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Units in Nernst Equation
Replies: 2
Views: 524

### Re: Units in Nernst Equation

It might be helpful to remember that 1 V = 1 J/C, and the units from the gas constant and Faraday constant will cancel out this way.
Tue Jan 19, 2016 7:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HW 8.59: standard reaction enthalpy
Replies: 1
Views: 463

### HW 8.59: standard reaction enthalpy

Hi! 4HNO3 (l) + 5N2H4 (l) --> 7N2 (g) + 12H2O (l) Why is it that once the individual components for the enthalpies of formation for the reactants/products are added up (and adjusted depending on stoichiometric coefficients and direction of reaction), the whole expression for standard reaction enthal...
Tue Jan 19, 2016 4:36 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HW 8.45: forming carbon disulfide
Replies: 1
Views: 320

### HW 8.45: forming carbon disulfide

Hello! 4C(s) + S8(s) --> 4CS2(l), deltaH = 358.8 kJ For part b (calculate heat absorbed in reaction for 197 g C) and part c (calculate how much CS2 was produced if heat absorbed is 415 kJ), why is it that we divide by the number of moles of C or CS2 respectively, rather than multiply, knowing that t...
Sat Dec 05, 2015 9:16 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Comparing pH and Ka
Replies: 1
Views: 468

### Re: Comparing pH and Ka

The pH decreases, meaning the solution is more acidic, as Ka increases. The pH and pKa can be related through the Henderson-Hasselbach equation, especially since at half the stoichiometric point, pH = pKa. Since stronger acids with high Ka values have weaker conjugate bases with low Kb values, the p...
Sat Dec 05, 2015 8:59 pm
Forum: Lewis Acids & Bases
Topic: Strength of Acids
Replies: 1
Views: 352

### Re: Strength of Acids

The strengths of the listed acids increase as there are more O atoms, because oxygen is highly electronegative and acts as an electron withdrawing group. Therefore, the conjugate base anions for these acids are more stable when there are more O atoms. In increasing order of acidity: HClO, HClO2, HCl...
Fri Dec 04, 2015 11:51 pm
Forum: *Titrations & Titration Calculations
Topic: Ions in acid base reactions
Replies: 2
Views: 462

### Re: Ions in acid base reactions

As a general rule, the anion components of strong acids and the cation components of strong bases act as spectator ions in the overall acid-base reaction. Since Cl- comes from HCl and and Na+ comes from NaOH, these ions do not participate in the reaction, and thus cannot affect the pH.
Fri Dec 04, 2015 11:43 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Buffer Region on a pH Curve
Replies: 2
Views: 744

### Re: Buffer Region on a pH Curve

The buffer region of the pH curve is the region in which lots of volume of the titrant is added with little change to the pH of the titrant-sample solution; on the graph, it appears as a relatively horizontal (flat) portion of the curve.
Tue Dec 01, 2015 1:15 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Increasing pressure
Replies: 2
Views: 508

### Re: Increasing pressure

Note that this is only true if the gas mixture reaction is at equilibrium before the pressure is changed, and if the pressure is increased by reducing the volume of the container, rather than by adding an inert gas to the container.
Tue Dec 01, 2015 1:07 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Pressure Change
Replies: 2
Views: 419

### Re: Pressure Change

Increasing the pressure of a gas mixture reaction at equilibrium by reducing the volume of the container (due to the inverse relationship between pressure and volume, shown by PV = nRT) favors whichever side of the reaction has a smaller number of moles of gas. Ex. A(g) + B(g) <--> 3C(g) Here, since...
Tue Dec 01, 2015 12:56 pm
Forum: Ideal Gases
Topic: Effects on Equilibrium constants
Replies: 2
Views: 476

### Re: Effects on Equilibrium constants

Thinking of "heat" as a reactant/product can make it easier to remember which direction an endothermic/exothermic reaction proceeds due to an increase/decrease in temperature. In an endothermic reaction, heat is absorbed; therefore, heat can be thought of as a reactant. Ex. A + B + heat --...
Tue Oct 27, 2015 8:32 pm
Forum: Ionic & Covalent Bonds
Topic: HW 3.25
Replies: 1
Views: 306

### HW 3.25

Hello!

In part c, aluminum hydride, hydrogen gains an electron, forming an anion, to make AlH3. In part d, hydrogen loses an electron, forming a cation, to make H2Te. Why is it that hydrogen acts differently in these two cases?
Tue Oct 27, 2015 8:15 pm
Forum: Ionic & Covalent Bonds
Topic: 3.21 Ground state
Replies: 5
Views: 902

### Re: 3.21 Ground state

If the molecule has an odd number of electrons (for example, NO2, nitrogen dioxide, has 17 electrons), then one of the electrons will be unpaired, and the molecule is a radical. If the molecule has an even number of electrons (for example, NO2-, nitrite ion, has 18 electrons), then all of the electr...
Tue Oct 27, 2015 8:08 pm
Forum: Bond Lengths & Energies
Topic: 3.87 Homework Problem
Replies: 3
Views: 979

### Re: 3.87 Homework Problem

Even though the above explanation is correct, I believe the solutions manual acknowledges that when the problem is approached in terms of electronegativity, CBr4 would have the strongest bond, rather than CF4. Because C and Br have the smallest difference in electronegativity (when compared to to C ...
Wed Oct 14, 2015 9:37 pm
Forum: Molarity, Solutions, Dilutions
Topic: G5 approach to question
Replies: 4
Views: 600

### Re: G5 approach to question

Why is it that when in part a, when we are asked to obtain a 2.12 mmol Na+ solution, and in part b, when we are asked to obtain a 4.98 mmol CO3^2- solution, that the solutions manual sets up ratios between Na+ and Na2CO2 and CO3^2- and Na2CO2, rather than Na2CO3?
Wed Oct 07, 2015 8:21 pm
Forum: Photoelectric Effect
Topic: Photoelectric effect post-quiz 17-19 [ENDORSED]
Replies: 6
Views: 4466

### Photoelectric effect post-quiz 17-19[ENDORSED]

Hi! Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. A. What is the kinetic energy of the ejected electron? B. How much energy is required to remove an electron from one sodium atom? C. What is the frequen...

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