CHEMISTRY COMMUNITY

Semi Yoon

Calculate the change in entropy when the pressure of 5.75g of helium gas is decreased from 320kPa to 40kPa while the temperature decreases from 423K to 273K. Assume idea behavior. I know that you should use two equations: deltaS=nRln(P1/P2) and deltaS=nCvln(T2/T1). Why would you use Cv and how would...

Semi Yoon

What is the difference between the rate law for formation of product and the experimental rate law? Would you solve for the rate law the same way for both?

Semi Yoon

On Worksheet 9, how would you solve for #7?

Semi Yoon

Do you include H+ in a cell diagram? Do you include all the products and reactants in a cell diagram except electrons?

Semi Yoon

How would you find the largest cell potential if assembled in an electrochemical cell?

Semi Yoon

Why would the precipitation of snowflakes inside a cloud at -10C and 0.839 atm be a spontaneous reaction?

Semi Yoon

When solving for deltaG, do you take into account the significant figures for temperature too?

Semi Yoon

Is there a way to quickly find which compound is reduced or oxidized in a reaction without having to calculate each oxidation state for each element?

Semi Yoon

If you see the standard reduction potential chart, the one with the higher (more positive) cell potential will be a stronger oxidizing agent while the one with the more negative cell potential will be a stronger reducing agent.

Semi Yoon

What is the different between standard reaction Gibbs free energy and and Gibbs free energy? How do we know when to use the standard cell potential for the equation for standard reaction Gibbs free energy?

Semi Yoon

Reaction 1: Fructose-6-phosphate +ATP --> Fructose-1,6-biphosphate + ADP deltaG = -13.7 kJ/mol Reaction 2: Fructose-6-phosphate + HPO4 2- --> Fructose-1,6-biphosphate +H20 deltaG = 16.5 kJ/mol Question: If the concentration of ATP is adjusted to four times its equilibrium concentration, what is the ...

Semi Yoon

Reaction 1: Fructose-6-phosphate +ATP --> Fructose-1,6-biphosphate + ADP deltaG = -13.7 kJ/mol Reaction 2: Fructose-6-phosphate + HPO4 2- --> Fructose-1,6-biphosphate +H20 deltaG = 16.5 kJ/mol To find the standard Gibb's free energy for ATP hydrolysis, my TA multiplied the Gibbs free energy of the f...

Semi Yoon

In a problem, if two initial and final values of temperature and volume are given in a problem in which two substances are mixed. Why would you need to solve for change in entropy using two equations (one with temperature and the other with volume) and add them together?

Semi Yoon

When enthalpy change and entropy change are negative, why does the spontaneity depend on temperature?

Semi Yoon

In the textbook, it states that Gibbs Free Energy tells us how much nonexpansion work we can get from the system. What does it mean by nonexpansion work?

Semi Yoon

When is the enthalpy of formation equal to the enthalpy of the reaction? Is it only when one mole of a product is produced?

Semi Yoon

In the equation: 2Al (s) + 6HCl (g) ---> 2AlCl3 (s) + 3H2 (g), the enthalpy of formation for AlCl3 is given as -704kJ/mol. The enthalpy of the reaction is given as well as -856 kJ/mol. To find the enthalpy of formation of gaseous hydrochloric acid, I know I would have to do the sum of the enthalpy o...

Semi Yoon

How do you know when the change in internal energy is equal to 0? Does it depend on if the system is open, closed, or isolated?

Semi Yoon

Crude petroleum is often contaminated by poisonous hydrogen sulfide gas. The Claus process for the extraction of sulfur from petroleum has two steps: 2 H2S(g) + 3 O2(g) ---> 2 SO2(g) + 2 H2O(l) 2 H2S(g) + SO2(g) ---> 3 S(s) + 2 H2O(l) How would you write a thermochemical equation for the overall rea...

Semi Yoon

Water gas is an inexpensive, low-grade fuel that can be made from coal. (a) Is the production of water gas exothermic or endothermic? How would you know? The reaction is C(s) + H2O(g) ---> CO(g) + H2(g) (b) How would you calculate the enthalpy change for the production of 200. L of hydrogen at 500. ...

Semi Yoon

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 of H2 were burned during ...

Semi Yoon

In the tissues the equilibrium H3O+ (aq) + HbO2- (aq) Δ HHb(aq) + H2O(l) + O2(aq) releases oxygen. When muscles work hard, they produce lactic acid as a by-product. (a) What effect will the lactic acid have on the concentration of HbO2- ? (b) When the hemoglobin returns to the lungs, where oxygen co...

Semi Yoon

Hydronium and hydroxide ions appear to move through water much faster than other kinds of ions. What explanation can you make from this observation? What does this mean?

Semi Yoon

What is the pH of each of the following diprotic acid solutions at 25 C: (a) 0.010 M H2CO3(aq);
(b) 0.10 M (COOH)2(aq); (c) 0.20 M H2S(aq)?

Semi Yoon

How would you calculate the pH of 0.15 M H2SO4(aq) at 25 C?

Semi Yoon

If a 15.5-g sample of CH3NH3Cl is dissolved in water to make 450. mL of solution, how would you find the pH of the solution?

Semi Yoon

How can you tell if an acid or base is strong or weak?

Semi Yoon

A reactor for the production of ammonia by the Haber process is found to be at equilibrium with PN2 = 3.11 bar, PH2 = 1.64 bar, and PNH3 = 23.72 bar. If the partial pressure of N2 is increased by 1.57 bar, how would you find the partial pressure of each gas once equilibrium is re-established?

Semi Yoon

If N2(g) + 3 H2(g) --> 2 NH3(g), K = 1.7 x 10^-3 at 600. K and 7.8 x 10^-5 at 700. K, and a gaseous mixture consisting of 2.23 mmol N2 and 6.69 mmol H2 in a 500.-mL container was heated to 600. K and allowed to reach equilibrium. Will more ammonia be formed if that equilibrium mixture is then heated...

Semi Yoon

At 500C, Kc = 0.061 for N2(g) + 3 H2(g) --> 2 NH3(g). If analysis shows that the composition of the reaction mixture at 500C is 3.00 mol*L^-1 N2, 2.00 mol*L^-1 H2, and 0.500 mol*L^-1 NH3, is the reaction at equilibrium? If not, in which direction does the reaction tend to proceed to reach equilibrium?

Semi Yoon

What is the acid and base in these reactions?
a. CH3NH2 (aq) + H30+ (aq) ---> CH3NH3+ (aq) + H20 (l)
b. CH3NH2 (aq) + CH3COOH (aq) ---> CH3NH3+ (aq) + CH3CO2- (aq)
c. 2 HI (aq) + Ca0 (s) ---> CaI2 (aq) + H20 (l)

Semi Yoon

How would you write a chemical reaction showing the proton transfer reaction of a cation or anion with water?

Semi Yoon

How would you write the balanced chemical equations for the reaction of 1 mol of formula units of each acidic oxide with 1 mol of water molecules to form an oxoacid and name the acid formed: (a) CO2; (b) SO3?

Semi Yoon

Which acid in each of the following pairs is stronger and explain why: (a) HF or HCl; (b) HClO or HClO2; (c) HBrO2 or HClO2; (d) HClO4 or H3PO4; (e) HNO3 or HNO2; (f) H2CO3 or H2GeO3.

Semi Yoon

Why do these acids have different strengths? (a) acetic acid and trichloroacetic acid; (b) acetic acid and formic acid.

Semi Yoon

How would you determine whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH<7 or pH>7, write a chemical equation to justify your answer. (a) NH4Br; (b) Na2CO3; (c) KF; (d) KBr; (e) AlCl3; (f) Cu(NO3)2.

Semi Yoon

How would you describe the structure of the formaldehyde molecule, CH2O, in terms of hybrid orbitals, bond angles, and pi- and sigma-bonds. The C atom is the central atom to which the other three atoms are attached.

Semi Yoon

For each of the following species: CH3 ; CH4; CH3 ; CH2; CH22 ; CH22, identify each as a radical or not. How would you rank them in order of increasing HCH bond angles?

Semi Yoon

If an organic compound distilled from wood was found to have a molar mass of 32.04 g·mol^-1 and the following composition by mass: 37.5% C, 12.6% H, and 49.9% O. What are the bond angles about the carbon and oxygen atoms? What is the hybridization of the carbon and oxygen atoms? Is the molecule pola...

Semi Yoon

Why would the molecule Benzyne, C6H4 be highly reactive?

Semi Yoon

How would you identify the composition of the bonds in the bonding in CH2=CHCHO and the hybridization of each lone pair?

Semi Yoon

How would you describe the structure of the CH3CN molecule in terms of hybrid orbitals, bond angles, and sigma and pi bonds when the N atom is a terminal atom?

Semi Yoon

How many numbers of electron pairs (both bonding and lone pairs) are there on the iodine atom in (a) ICl2 ; (b) ICl4 ;(c) ICl3; (d) ICl5?

Semi Yoon

Which of the following species are radicals? (a) NO2 ;(b) CH ; (c) OH; (d) CH O. and why?

Semi Yoon

On the basis of the expected charges of the monatomic ions, what is the chemical formula of each of the following compounds: (a) thallium(III) chloride; (b) aluminum sulfide; (c) manganese(IV) oxide?

Semi Yoon

What is the ground-state electron configuration and number of unpaired electrons expected for each of the following ions: (a) Ca2 ; (b) In ; (c) Te2 ; (d) Ag?

Semi Yoon

For each of the following ground-state atoms, what is the type of orbital from which an electron will need to be removed to form the +1 ions: (a) Zn; (b) Cl; (c) Al; (d) Cu?

Semi Yoon

What is the ground-state electron configuration expected for: (a) Cu ; (b) Bi3 ; (c) Ga3 ; (d) Tl3?

Semi Yoon

In the heavier transition-metal elements, especially the lanthanoids and actinoids, there are numerous exceptions to the regular order of orbital occupation predicted by the building- up principle. Why would more exceptions would be noted for these elements?

Semi Yoon

Ionization energies usually increase on going from left to right across the periodic table. The ionization energy for oxygen, however, is lower than that of either nitrogen or fluorine. How do you explain this anomaly?

Semi Yoon

What is a diagonal relationship? How does it arise? What are two examples that illustrate this concept?

Semi Yoon

Why does the extent of change in the electrical field at a given point decrease when the frequency of the electromagnetic radiation decreases?

Semi Yoon

What does it mean when light has high intensity? How is high intensity light different?

Semi Yoon

Is the intensity of photons related to the amplitude of a wave?

Semi Yoon

A lamp rated at 32 W emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval?

Semi Yoon

Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by an excited sodium atom when it generates a photon?

Semi Yoon

How can we classify if a particle has any measurable wavelike properties? Why aren't we able to measure wavelike properties of a moving particle if it is too small?

Semi Yoon

Copper (II) nitrate reacts with sodium hydroxide to produce a precipitate of light blue copper (II) hydroxide. (a) How would know how to find the chemical equation for this reaction?

Semi Yoon

A reaction vessel contains 5.77g of white phosphorus and 5.77g of oxygen. The first reaction to take place is the formation of phosphorus (III) oxide, P406:P4(s) + 302 (g) ---> P4O10 (s). (a) What is the limiting reactant for the formation of P4O10? (b) What mass of P4O10 is produced? (c) How many g...

Semi Yoon

A stimulant in coffee and tea is caffeine, a substance of molar mass 194 g mol 1. When 0.376 g of caffeine was burned, 0.682 g of carbon dioxide, 0.174 g of water, and 0.110 g of nitrogen were formed. How would you find the empirical and molecular formulas of caffeine, and write the equation for its...

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