CHEMISTRY COMMUNITY

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Textbook Question:"An experimental automobile burns hydrogen for fuel. At the beginning of a test drive, the rigid 30.0-L tank was filled with hydrogen at 16.0 atm and 298 K. At the end of the drive, the temperature of the tank was still 298 K, but its pressure was 4.0 atm. (a) How many moles o...

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Why is it that the heat of the ice cube requires two calculations being as opposed to water's one? I understand the the ice is undergoing a phase change; however, I am unsure as to why we add the second calculation of ice? Additionally, is the negative sign on the side of ice, -qice=qwater, because ...

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Yes! It is cumulative!

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If the question were to say, "determine the time needed for the concentration of SO2Cl2 to decrease to 20%", would we use ln20 rather than ln10? Is the number following ln that of the percent?

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For number 17, when determining the order for reactant B, why did they use experiments 2 & 3 rather than 1 & 3? Does it matter?

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The final is cumulative, but like last quarter in 14A it focuses on the new content a little more.

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For the question regarding pH, which equation and steps were necessary to determine the answer?

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It is posted on Dr. Lavelle's 14B website. Gibbs Free Energy and Cell potentials!

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Yes, cell potentials do not take into consideration the balance of the equation as it is an intensive/fixed property. The only thing that changes the value is whether or not you need to change the sign to negative to represent an oxidation reaction.

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You essentially need to make sure the overall charge including all positives and negatives from hydrogen ions an hydroxide ions are included. For acidic redox reactions specifically, -OH does not contribute to your balancing count as it is usually not in an acidic redox reaction equation. So, you're...

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Why is it that heat lost by the metal(a positive value)=-heat gained by water??? shouldn't it be reversed since heat is LOST (-) by metal??

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I keep plugging in (1)(219.2)(163)+(6)(29.4)(163) but not getting the correct answer?

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Im a little confused as to what values of final and initial moles to use in calculating the work through -(delta)RT?

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I don't understand the values for the temperature change used for the first enthalpy changes where glucose and oxygenate added together? Where did 11.3 for glucose and 16.3 for oxygen come from?

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I don't understand how to calculate the entropy change for temperature change to obtain 3.48J/K. Can someone explain how to derive that answer?

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I am having trouble understanding how to calculate the answer. Can someone explain?

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Are there any study guide/review sheets the TAs have made available for the midterm?

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Can someone please explain the logical approach to this question?

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I suppose I am confused on how to know when to use the equation w=-PexdeltaV vs w=-nRTln(final/initial)?

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For the midterm, does the content we are being tested on include thermochemistry, equilibrium and acid/base only? And as far as acid base, should we know Henderson-Hasselbalch?

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Gibbs free energy is essentially a measure of how much work/energy is available to be done by a system. When you have a (-) Gibbs free energy, the reaction is exothermic and essentially spontaneous. When the value is (+), the reaction is endothermic and non-spontaneous. By spontaneity, it means that...

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Dr. Lavelle thoroughly explained why steam burns more than ___? I was absent that day and was wondering if someone could thoroughly explain the conceptual basis of that discussion?

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How do we know when to use K vs the Kc value from the table?

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Why did we assume it was a synthesis reaction? What it be the same Kc if we solved it as a decomposition reaction where HI is broken down?

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How does flask 3 represent equilibrium?

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Why does the Na+ get omitted from the CH3Co2??? Is this the case for every compound we are given. I guess I am just confused on how to accurately utilize the Ka values list when the compounds listed are a bit different from those given to us in the questions.

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I don't understand why the Ka value used for part b is different in terms of the exponent compared to the one provided by the textbook?

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Why is water not included in the constant?

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for the equation 6CO2(g)+6H2O(l)-->C6H12O6(aq) + 6O2(g), would the system being compressed mean that the volume decrease and pressure increases? As a result, since technically liquid isn't included in the equilibrium constant, shouldn't equilibrium favor the reactants??

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I don't understand how to know if the equation we derived from A-->B+C has coefficients as the true answer?

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How is the following true?
-If one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger.

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Determine whether the following statements are true or false:
a. When chemical equilibrium is reached, the composition of the reaction mixture remains constant.
b. If we make a reaction go faster, we can increase the amount of product at equilibrium.

Which is true/false?

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During the first lecture, Dr. Lavelle noted that the products were more stable than the reactants? Is this ALWAYS the case? Or was it simply because the diagram he drew was exothermic?

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So, essentially, the ratios of concentration between the products and reactants of a reaction at equilibrium do not change in spite of changes in the coefficient that may change in the equation?

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Why did the LDF forces overrule the dipole-dipole interactions to make H2Se to have a greater boiling point?

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"Microwave ovens heat food by exciting water to a higher vibration mode....... What is the energy and wavelength of this radiation?" For this question, I used the Einstein equation to solve for the energy and got it correct; however, looking back to review, I recall being told that that eq...

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Why is carbon the central atom in ClCN and not in HCN?

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How exactly would the lewis structure for (CH3)2Be look like?

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When determining the bond angle of a moleucule, for example, SOCl2, do we consider the atom arrangement (tetrahedral with 109.5 degree bonds) or the actual shape's (trigonal pyramidal) bond angle? I know the answer is slightly less than 109.5 but im not completely sure why?

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Does the concept of conjugate acids and bases only apply to Lewis acid and bases or is it inclusive to bronsted acid and bases?

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Just to confirm, the reason why bond angles vary is based on the electron-electron repulsion due the presence of lone pairs on each distinct structure, correct?

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Why is it that the Hydrogen is bonded to the oxygen rather than the carbon in HOCO?

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Hi, I recently asked my professor for my 5-6:15 English class if I would be able to leave class a bit early to make it to my chemistry midterm at 6pm. She responded saying I needed to work it out with my chemistry professor/proctor of the exam. I am unsure of what to do at this point? Are there exam...

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I was wondering why the Rydberg equation is being set up to be equal to nu (v)? What is the correlation? Also, would a question like this ever be on an exam?

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I did my research on the forum on how to do this problem; however, the approach taken in the solutions manual uses the shortcut equation that Dr. Lavelle frowned upon. How can I solve this problem using the approach he uses with the equation En=-hR/n^2 as opposed to nu=R(1/n^2-1/n^2)?

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On M.5, the question asks to determine how many moles of each product will be produced. What I did is perform a mole to mole ratio by multiplying 5mol of BrF3 by the 6 moles of ClO2F and dividing that by 2 mol BrF3 to obtain the moles of ClO2F left. I got 15 moles for ClO2F but the solutions manual ...

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When given a chemical equation like 6 CO2 + 6 H2O → C6H12O6 + 6 O2, the ratio between CO2 and H20 is 1:1. However I have seen in a few post-module questions that it asks about the mass of, perhaps, of O2 when given 3 moles of CO2 and 6 moles of H20. When it says three moles of CO2, do I disregard th...

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