Thursday
July 31, 2014

Posts by Ana


Total # Posts: 966

Physics
A boat is moving 24.4m/s, 35 degrees North of East against the 10m/s water current that flows towards south. What would be the speed of the boat as it crosses the river

PHYSICS
a girl weighing 620 n sits in the middle of a 2.8 m long hammock which sags 1.2m below th e point of support. What force is exerted by each of the two ropes supporting the hammock

statistics
predict the score in statistics for a student whose score in mathematics is 30

(2-8) Chemistry - Science (Dr. Bob222)
Thank you for your explications. Could you tell me if the expansion of a gas into the vacuum would be considered zero work?

(2-8) Chemistry - Science (Dr. Bob222)
Also, could you tell me please what processes would result in work=0 (beside the constant volume)?

(2-8) Chemistry - Science (Dr. Bob222)
Ahhhh, I got it now. I should have been more careful on my reading. Thank you

(2-8) Chemistry - Science (Dr. Bob222)
Thank you for your answers. Dr.Bob, you said that "q changes with T", thus dE changes with T, then why the answer D in the problem below is not true. IT is just a bit confusing, thank you. In heating an ideal gas, A) It takes more heat to raise T by one degree K in c...

(2-8) Chemistry - Science (Dr. Bob222)
Which of the following statements is correct? A) The internal energy of a system increases when more work is done by the system than the heat that flows into the system. B) The system does work on the surroundings when an ideal gas expands against a constant external pressure...

Chemistry - Science (Dr. Bob222)
Liquid chloroform (CHCl3) is placed in a closed container and allowed to equilibrate with chloroform vapor. With the temperature held constant, additional chloroform is introduced into the system, and the vapor-liquid equilibrium is reestablished. Following this, the chlorofor...

(1-22)Chemistry - Science
True. Will do so

(1-22)Chemistry - Science
Thank you Dr.Bob222 for clarification. I am reviewing all the information for Gen Chem 2 for a big exam next week; and as you know the information is quite vast and it takes a bit to recall how to solve the problems correctly. I do not seek for mere answers to these problems, ...

(1-22)Chemistry - Science
Consider the following reaction: C(s) + H2O (g) ⇌ CO (g) + H2 (g) (Kp = 0.45 at 900 K) What is the equilibrium partial pressure of H2O when the initial partial pressure of water is 1.00 atm? a) 0.43 atm b) 0.58 atm c) 0.22 atm d) 0.52 atm e) 1.16 atm

(1-17)Chemistry - Science
Consider the reaction: SO2 (g) + NO2 (g)  SO3 (g) + NO (g) At T = 1000 K, where the reaction is exothermic with an equilibrium constant K = 9.00 If the reaction vessel is instead charged initially with SO3(g) and NO(g), each at a partial pressure of 0.500 atm, the part...

(1-16)Chemistry - Science
Consider the reaction: SO2 (g) + NO2 (g) ==> SO3 (g) + NO (g) At T = 1000 K, where the reaction is exothermic with an equilibrium constant K = 9.00 The reaction vessel is charged initially with all four gases, each at a pressure of 0.5 atm. After equilibrium is achieved, th...

(1-15) Chemistry - Science
The answer is C but not sure why so

(1-15) Chemistry - Science
Assume a gas of molecular mass M g/molecule obeys the Maxwell Boltzmann distribution of speeds at temperature T. If u2> u1, the ratio of the number of molecules at speed u2 to the number at speed u1 a) is always less than one. b) is always greater than one. c) can be either...

(1-13) Chemistry - Science
Which of the following effects will make the ratio (PV) / (nRT) less than 1 for a real gas? a) The gas molecules are large enough to occupy a substantial amount of space. b) A large number of molecules have speeds greater than the average speed. c) The gas molecules have a ver...

1-12. Chemistry - Science
At STP, 3.0 L of D2 reacts completely with 3.0 L of E, producing 1.5 L of a product. What is the formula of the product?

(1-11) Chemistry - Science (Dr. Bob222)
Will the Le Chatelier's principle work here? Because pure liquid has no effect on the equilibrium position, it will not move towards products; thus, chloroform vapor will not form.

(1-11) Chemistry - Science (Dr. Bob222)
Liquid chloroform (CHCl3) is placed in a closed container and allowed to equilibrate with chloroform vapor. With the temperature held constant, additional chloroform is introduced into the system, and the vapor-liquid equilibrium is reestablished. Following this, the chlorofor...

Chemistry - Science (Dr. Bob222)
Nitrogen gas has values of Cv and Cp of 20.8 and 29.1 J K-1 mol-1, respectively. When a certain amount of nitrogen is heated at constant pressure, what fraction of the heat Q is used to increase the internal energy of the gas, and how is the remaining energy used? A) 3/2 of Q ...

Chemistry - Science (Dr. Bob222)
Hydrazine is used as a rocket fuel because its reaction with oxygen is extremely exothermic: N2H4(liquid) + O2(g)  N2(g) + 2H2O(liquid) ΔH(reaction) = -615 kJ mol-1 What is the enthalpy of this reaction if water were produced in the gaseous rather than the liquid ...

(12)Chemistry - Science (Dr. Bob222)
This problem is quite confusing. Thank you for your contribution and elucidation!

(12)Chemistry - Science (Dr. Bob222)
...not sure how to derive it

(12)Chemistry - Science (Dr. Bob222)
I have solved it this way too and I got answer A: -7740 J, but the correct answer is actually C :(

(12)Chemistry - Science (Dr. Bob222)
Thank you Devron for this clarification.

(12)Chemistry - Science (Dr. Bob222)
Calculate delta E for a process in which 88.0 g of nitrous oxide gas (N2O) is cooled from 165 ˚C to 65 ˚C at a constant pressure of 5.00 atm. The molecular weight of nitrous oxide is 44.02 g/mol, and its heat capacity at constant pressure, Cp, is 38.70 J/molK. A) - 7...

(23.Chemistry - Science (Dr. Bob222)
This Q. seemed too easy to me, and I though it must be a trick question or something, nonetheless thank you for explaining.

(23.Chemistry - Science (Dr. Bob222)
Thank you Devron for explication.

(23.Chemistry - Science (Dr. Bob222)
The correct answer is D. But my question is how is it possible to have an initial voltage of 1.1V for the cell is with concentration of 1M, if E standard for the cell is 0.48. I am sure I am missing something here.

(23.Chemistry - Science (Dr. Bob222)
An electrochemical battery made from Sn and Cu electrodes under standard conditions shows an initial voltage of V= 1.1 V. If the concentration of both Cu2+ and Sn2+ solutions is increased to 2 M from 1 M, the observed voltage will: (Hint: use the Nernst equation) A. increase ...

(19) Chemistry - Science (Dr. Bob222)
Good morning, Could you please let me know how did you calculated K for answer D and C. Thank you.

(19) Chemistry - Science (Dr. Bob222)
Use the following information to answer this question: Cu+(aq) + e- → Cu(s) E° = 0.521V Cu2+ (aq) + e- → Cu+ (aq) E° = 0.153 V. Given these half cell reactions, an aqueous solution of Cu+ ion in the absence of O2(g) : A. will be thermodynamically stable B. ...

(11) Chemistry - Science (Dr. Bob222)
Yes, A! Thank you for making it easy to understand.

(11) Chemistry - Science (Dr. Bob222)
The correct answer is A, which I got it right, but I was torn between A & B. could you please explain why B is incorrect. Thank you.

(11) Chemistry - Science (Dr. Bob222)
In the following hypothetical reaction A + B → C + D, the equilibrium constant, Keq is less than 1.0 at 25°C and decreases by 35% on changing the temperature to 45°C. What must be true according to this information? A. The ΔH° for the reaction is negati...

Chemistry - Science (Dr. Bob222)
Thank you!

Chemistry - Science (Dr. Bob222)
Hello, how are you? The correct answer to this Q is E. but I have chosen B. Could you please explain why all of them cannot be true? Thank you

Chemistry - Science (Dr. Bob222)
The following reaction has a positive value of ΔG°. 2H2O(g) → 2H2(g) + O2(g) Which of the following statements must be true? A. The reaction is slow. B. The reaction will not occur. That is, when H2O(g) is introduced into a flask, no O2 or H2 will form even over...

(5) Chemistry - Science (Dr. Bob222)
aha very interesting, thank you so much for this detailed explanation, now I get it.

(5) Chemistry - Science (Dr. Bob222)
Also, could you tell me please how you have solved for X?

(5) Chemistry - Science (Dr. Bob222)
P.S. I just found out that our calculation were right all along for Zn/Cu cell problem... indeed the answer is 1.09V =) Thank you!

(5) Chemistry - Science (Dr. Bob222)
This is a beautiful way of thinking, thank you for sharing. The problem is that at the test I am not given the Ka value for the acid. I solved it this way: I used HH equation, then since we are dealing with the same acid the value of Ka would not change (i thought of it as coa...

(5) Chemistry - Science (Dr. Bob222)
Consider a buffer made from 0.13 M sodium acetate and 0.10 M acetic acid in 1L. What amount of KOH must be added to cause an increase of the pH by 0.14? A) 0.048 mol B) 0.038 mol C) 0.028 mol D) 0.018 mol E) 0.008 mol

Chemistry - Science (Dr. Bob222)
Ammonia is a weak base with a Kb of 1.8 x 10-5. A 100.0 mL sample of 0.13 M aqueous solution of ammonia (NH3) is mixed with 87 mL of 0.15 M solution of the strong acid HCl, calculate the pH of the final solution. A) 2.9 B) 11.1 C) 8.8 D) 5.2 E) None of the above

Chemistry - Science (Dr. Bob222)
Thank you! I finally have solved it

Chemistry - Science (Dr. Bob222)
the correct answer is 5.2 mmol; however, I get lost in the calculations. It seems easy to solve: I have pH, pKb, and HH eq, but then I get stuck to derive x correctly

Chemistry - Science (Dr. Bob222)
How many mmol ( millimoles) of HCl must be added to 130.0 mL of a 0.40M solution of methyl amine (pKb = 3.36) to give a buffer having a pH of 11.59? Thank you for your help!

Chemistry - Science (Dr. Bob222)
Posted by Ana on Saturday, May 3, 2014 at 11:23am. A zinc-copper battery is constructed as follows (standard reduction potentials given below): Zn | Zn2+ (0.10 M) || Cu2+ (2.50 M) | Cu Zn2+ + 2 e- → Zn(s) Eº = -0.76 V Cu2+ + 2 e- → Cu(s) Eº = 0.34 V The m...

Math
If a navigation error puts a plane 2 degrees off course, how far off course is the plane after flying 121 miles? Round to the nearest tenth of a mile. Just explain how to solve, please.

Math
A boat travels 74 miles on a course with direction 34 degrees and then changes its course to travel 58 miles at 53 degrees. How far north and how far east has the boat traveled on its 132-mile trip? A 87.7 miles east and 44.3 miles north B 35.7 miles east and 96.3 miles north ...

Math
An airplane, after 1 hour in the air, arrives at a point 350 miles south of its departure point. There was a steady wind of exactly 25 mph from the northwest during the entire flight. Which represents the airplane's average air speed?

Chemistry - Science (Dr. Bob222)
thank you!!

Chemistry - Science (Dr. Bob222)
Ammonium metavanadate reacts with sulfur dioxide in acidic solution as follows (hydrogen ions and H2O omitted): xVO3^–^ + ySO2 → xVO^2+^ + ySO4^2–^ What is the ratio of x : y? A. 1 : 1 B. 1 : 2 C. 2 : 1 D. 1 : 3 E. 3 : 1

Chemistry - Science (Dr. Bob222)
Thank you for such a great response! You are a legend!

Chemistry - Science (Dr. Bob222)
the correct answer is D, but i am confused on the rational here. Not sure what the professor wants me to understand here, the concept behind...

Chemistry - Science (Dr. Bob222)
Use the following information to answer this question: Cu+(aq) + e- → Cu(s) E° = 0.521V Cu2+ (aq) + e- → Cu+ (aq) E° = 0.153 V. Given these half cell reactions, an aqueous solution of Cu+ ion in the absence of O2(g) : A. will be thermodynamically stable B. ...

chemistry - Science
Disregard of 1M solution, it's a typo. The volume of 1.00L is relevant

chemistry - Science
A zinc-copper battery is constructed as follows (standard reduction potentials given below): Zn | Zn2+ (0.10 M) || Cu2+ (2.50 M) | Cu Zn2+ + 2 e- → Zn(s) Eº = -0.76 V Cu2+ + 2 e- → Cu(s) Eº = 0.34 V The mass of each electrode is 200 g. Each half-cell cont...

chemistry - Science
A zinc-copper battery is constructed as follows (standard reduction potentials given below): Zn | Zn2+ (0.10 M) || Cu2+ (2.50 M) | Cu Zn2+ + 2 e- → Zn(s) Eº = -0.76 V Cu2+ + 2 e- → Cu(s) Eº = 0.34 V The mass of each electrode is 200 g. Each half-cell cont...

Chemistry - Science
A fuel cell designed to react grain alcohol with oxygen has the following net reaction: C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) The maximum work that 1 mol of alcohol can yield by this process is 1320 kJ. What is the theoretical maximum voltage this cell can achieve?

chemistry - (Dr. Bob222)
Thank you so much! This makes much more sense now. Indeed a great tool to know

chemistry - (Dr. Bob222)
Thank you very much! The formula is very useful,but if it's no trouble for you could you please explain the concept?

chemistry - (Dr. Bob222)
A student attempted to synthesize malonic acid which has a molecular weight of 104 g/mol by the same method used to synthesize aspirin. A titration was performed to find the equivalent weight. 0.125 g of malonic acid product was used for a titration that required 24 mL of 0.10...

College Chemistry (DrBob222)
Thank you! You are legendary!

College Chemistry (DrBob222)
The decomposition of HCO2H follows first-order kinetics. HCO2H(g) CO2(g) + H2(g) The half-life for the reaction at a certain temperature is 44 seconds. How many seconds are needed for the formic acid concentration to decrease by 73%?

chemistry - (Dr. Bob222)
No, they did not provide any reaction for this problem. If I'll find the solution, I'll post it here. Thank you for your help.

chemistry - (Dr. Bob222)
I did that and but I got 1.52 mol/L rather 0.97 (as the answer key provides it)

chemistry - (Dr. Bob222)
The rate constant for a second order reaction has the value of 2.5 x 10–3 L·mol–1·s–1. If the initial concentration of reactant is 3.5 mol·L-1, what will be the molar concentration of the reactant after 2.5 minutes?

Chemistry - Science (Dr. Bob222)
I have calculated K1 and K2 by dividing initial rate to initial concentration [A2], and I solved for Ea but for some reason I don't get the right answer, (which is 10.2KJ)

Chemistry - Science (Dr. Bob222)
Consider the kinetic data given in the table below for the first order reaction: What is the value of the activation energy? A_2_--> 2A Expt. Initial [A2] Temp. Initial Rate mol/L (°C) [A2]·s–1 1 0.10 100 1.2 x 10–3 2 0.20 200 4.8 x 10–3 3 0.15 ? 4...

Chemistry - Science (Dr. Bob222)
Consider the kinetic data given in the table below for the first order reaction: What is the value of the activation energy? A_2_--> 2A Expt. Initial [A2] Temp. Initial Rate mol/L (°C) [A2]·s–1 1 0.10 100 1.2 x 10–3 2 0.20 200 4.8 x 10–3 3 0.15 ? 4...

chemistry
a 0.0500 mol sample of a nutrient substance is burned in a bomb calorimeter containing 2.00 x 10^2g H2O. If the formula weight of this nutrient substance is 114g/mol, what is the fuel value (in nutrient Cal) if the temperature of the water increased 5.70C

Math
Use synthetic division to determine which pair of integers provide both a lower and an upper bound for the zeros of f(x)= x^5-2x^4-25x^3+50x^2+144x-290 PLEASE SHOW WORK!!!

Subtracting Fractions with like Denominators
If Lori's neighbor gave her sixths eighths cup of milk, would she then have enough milk to make her 2 pancakes?

french
Do this sentence is direct or indirect je vais voir mes cousins

Physics
if you throw a 0.2 kg ball straight up at 8 m/s how high will it go

physics
What are the principles behind seatbelts and air bags that make passengers safer in a collision?

physics
If a motorboat travels 25km/h towards the sea, down a river whose velocity is 4km/h what is the boats velocity related to the shore? A, 21 km/h B, 29km/h C, 25 km/h D, 4 km/h

physics
if an airplane is traveling at 550 km/h into a head wind with a velocity of 40km/h what is the airplanes velocity relative to the ground

Physics
If a motorboat travels 25km/h towards the sea, down a river whose velocity is 4km/h what is the boats velocity related to the shore?

Chemistry
How many copper atoms are in a pure copper statue with a mass of 139kg{\rm kg}

Chemistry
Iron ores have different amounts of iron per kilogram of ore. Calculate the mass percent composition of iron for each iron ore: Fe2O3{\rm Fe_2O_3} (hematite), Fe3O4{\rm Fe_3O_4} (magnetite), FeCO3{\rm FeCO_3} (siderite).

Chemistry
Citric acid, the compound responsible for the sour taste of lemons, has the following elemental composition: C{\rm C}, 37.51%\%; H{\rm H}, 4.20%\%; O{\rm O}, 58.29%\%.Calculate the empirical formula of citric acid

statistics
Suppose a manufacturer claims that each family-size bag of pretzels sold weighs 12 ounces on average with a standard deviation of 0.8 ounces. A consumer's group decides to test this claim. If a simple random sample of 49 bags of pretzels gives a sample mean of 11.8 ounces,...

chemistryyyy
(a) What is the pH of a 6.1 ✕ 10-5 M Ca(OH)2 solution? (b) What is the H3O+ concentration of the solution? I already know the answer to part A, I just don't understand how you could use that information to find the concentration of H30+ when its not in the ionic equ...

chemistryyyy
Thanks! I got part A but how are you supposed to know the concentration of H30+ if its not in the equation?

chemistryyyy
a. What is the pH of a 6.1 ✕ 10-5 M Ca(OH)2 solution? b. What is the H3O+ concentration of the solution? I just cant figure out the ionic equation.

Physics
Canadian geese migrate essentially along a north-south direction for well over a thousand kilometers in some cases, traveling at speeds up to about 100 km/h. If one such bird is flying at 100 km/h relative to the air, but there is a 38.0km/h wind blowing from west to east. a) ...

Physics
A canoe has a velocity of 0.410m/s southeast relative to the earth. The canoe is on a river that is flowing at 0.510m/s east relative to the earth. Find the magnitude of the velocity v⃗ c/r of the canoe relative to the river

Algebra 2
A ball is dropped from 400 ft what is the height of the ball on the 6th bounce? 1 bounce =280 ft 2 bounce= 196 ft 3 bounce = 137.2 How do I figure this out?

Biology
what is independent variable definition?

english
Please HELP Type the word that the underlined phrase modifies or renames. Store the records OF PAYMENTS in the file cabinet. Question 24.. Type the word that the underlined phrase modifies or renames. The house, AN OLD FASHIONED COTTAGE SURROUNDED BY CREPE MYRTLESs, was charming.

chemistry
Acetic acid (CH3CO2H) is a weak acid. As a result, a solution of sodium acetate (NaCH3CO2) will be _____.

Math
(1) 8/1 divided (-3 2/5) My answer is 68/1 (2) 3 2/3 divided by -8 6/7 answer 682/21 3) 41/5 x -8/5 =32/25 Please I need help i'm so confused please show work so I can understand these other 27 problems that i have to complete. Thank you Ms. Sue

Compters
The major reason for the predominance of the PCI bus in the latest models of PCs is that A. the size and form factor make it easy to package. B. it's exclusively manufactured in the USA. C. the technology was released as open source. D. it uses ASSEMBLER language commands.

Math
If x over three minus y over two= negative three. Which statement best explains the value of y changes each time x is increased by one unit? A. The value of y increase by three over two units. B. The value of y increase by two over three units. C. The value of y decrease by th...

Science
How is Earth like a system?

french
Tu viens d'ou? Comment est CE que le Prof skie? Ou est-CE que tu vas? les crêpe coutent combines? Vous allez a l' Ecole, n'est CE pas?Avec qui est- CE que tu joues au foot? Tu es le professeur match the question question with the letter appropriate answer.tre...

french
Match the question with the letter of the appropriate answer pourquoi est - CE que tu e' tudies le francais

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