Ice-cream

For the dissociation reaction of the acid HF: HF(aq) --> H+(aq) + F-(aq) DeltaS is observed to be negative. The BEST explanation for this is: a) This is the expected result since each of the HF molecule produces two ions when it dissociates. b) Hydration of the ions produces the negative value of deltaS. c) The reaction is expected to be exothermic and thus deltaS should be negtaive. d) The reaction is expected to be endothermic and thus deltaS should be negative. e) None of these explain the negative value of deltaS. Can someone please help me with this question? What I know so far is that if deltaS is negative, the reaction must not be spontaneous. I know the formula deltaS(surroundings) = -deltaH / temperature....but that is for the entropy of the surroundings and not for the system....so I think maybe c) and d) are probably both incorrect because the deltaS they are referring to should be for the system. I really have no idea what a) and b) are talking about.... Any help would be greatly appreciated. Thanks

Does that mean its Cl+...coz electrophiles want e- so they would be positively charged?...i dont think its AlCl4+...is that right?

Can anyone help me with this question? Which is the active chlorinating species in aromatic chlorination reactions using chlorine in the presence of aluminium chloride? AlCl4+ Cl- AlCl4- Cl+ HCl

"a garden hose is attached to a water faucet on one end and a spray nozzle on the other end. The water faucet is turned on but the nozzle is turned off so that no water flows through the hose. The hose lies horizontally on the ground and a stream of water sprays vertically out of a small leak to a hieght of 0.75m. What is the pressure inside the hose? [ans: 7.4kPa]" i really have absolutely no idea with this question.i know this is to do with bernoulli's equation but i really still don't have a clue. does anyone have any idea? also, "an object executing simple harmonic motion has a maximum speed v[max] and a maximum acceleration a[max], find the period of this motion. express your answers in terms of v[max] and a[max]." im also having trouble with this question. i can find the time by going v / a...but thats time, not period...any ideas guys?

Can anyone help me with these 2 questions? 1. "You step into an elevator holding a glass of water filled to a depth of 6.5cm. After a moment, the elevator moves upward with constant acceleration, increasing its speed from zero to 2.2m/s in 3.1s." a) During the acceleratrion, is the pressure exerted on the bottom of the glass greater than, less than, or the same as before the elevator began to move? Explain. (I know it should be greater...but I didn't come to that conclusion by thinking in terms of forces, pressure, depth etc...in a physics way. can someone explain it in the "physics" way?) b) Find the pressure exerted on the bottom of the glass as the elevator accelerates. (I think that the initial pressure would be the atmospheric pressure + density x gravity x height...but i'm not sure what would happen during the acceleration. I can find the value of the acceleration...but...how does it fit in?) 2. A 0.12kg balloon is filled with helium (density = 0.179kg/m^3). If the balloon is a sphere with a radius of 5.2m, what is the maximum weight it can lift? (i thought that all i'd have to do is use density = m/v where density is given and volume is 4/3 pi r^3 but i get 105.43kg which means the weight is 1054N but the answer is 5.7kN. can any1 see what i'm doing wrong??)

Four point charges, each of magnitude q are located at the corners of a sqaure with sides of length a. Two of the charges are +q and two are -q. The charges are arranged in one of the following two ways: 1. The charges alternate in sign (+q,-q,+q,-q) as you go around the sqaure. 2. The top two corners of the square have positive charges (+q,+q) and the bottom two corners have negative charges (-q,-q). a) Which case will the electric field at the centre of the square have the greatest magnitude? b) Calculate the electric field at the centre of the square for each of these two cases. I really have no idea for the parts of this question. Can any1 give me any starters tips or just point me in the right direction for thinking? also, i have another question: Two identical point charges in free space are connected by a string 6.6cm long. The tension in the string is 0.21N. Find the tension in the string if +1.0microC of charge is transferred from one point charge to the other. what im not sure is what they mean by the charge being "transferred from one point charge to another"...can any1 explain? thanx

hey thanx! i get now!

"A point charge q = -0.35nC is fixed at the origin. Where must an electron be placed in order for the electric force acting on it to be exactly opposite to its weight? (Let the y axis be vertical and x axis be horizontal)" [ans: 240km above q] my question is, i've found 240km using coloumb's law...but im not sure about the direction...how com the answer is 240km "above q"??

with the equilibrium constant, when K<1 the reactants are favoured, when K>1 the products are favoured but when K=1...what happens? also, does any1 know whether the terms "carbanion" and "carbocation" refer to a whole molecule or just to the C in the molecule?

hey does any1 know that out of acyl chloride, amide, acyl anhydride, ketone and ester...which one won't undergo hydrolysis? do carboxylic acids and their derivatives always undergo hydrolysis? thanx

1. the radius of an argon atom is 4.2e-8 cm. What percent of the total volume of a 1 mol sample of argon gas at STP is occupied by the argon atoms? [0.83] im really stuck on this one! 2. calculate the P[total] in atom for a mixture of 3 gases that have partial pressures of 72cmHg, 400mmHg and 0.65mHg respectively.[ans:2.33] dont i just add those up and then divide by 760 to change to atm?? coz that doesnt give me the right ans. 3. A volume of 10cm^3 each of O2 gas and CO gas at STP are mixed in a 20cm^3 container and allowed to react at constant temperature to yield CO2. Calculate P[total] in atm after the reaction is complete. [ans: 0.75] i thought P1V1 = P2V2 so for one of the gases, say O2, P2 would be 0.5 coz P1 = 1atm, V1 = 10, V2 = 20...then since volumes of both gases are equal, both would have partial pressure of 0.5 so total pressure would be 1.

hey can any1 explain to me briefly what anabolic steroids do in relation to GnRH, i think something about them causing the GnRH to release more estrogens and testosterones and that they ignore the negative feedback mechanism in our body...but im not too sure...

hey i have this question relating to probability plots... my teacher said that if you see a j shape (where the head of the j would be at the top right corner and the tail of the j would be at the bottom left corner, along the diagonal probability plot) in a probability plot, then that means the data is skewed...except she said that its skewed in the direction of the j...does any1 know any websites that would explain it better, or can any1 explain it to me? thanx

wow! thanks heaps! i can't believe i didn't see that, no wonder i was getting all these similar Q wrong!

hey guys, ive got this question which i know it should be pretty straight forward but for some reason, i cant get the answer: Calculate the ionisation energy in kJ for a mole of hydrogen atomst that are in the n=2 energy level. I think i just use E = -2.18e-18 Ze2 (1/nfinal - 1/ninitial) what i did was substitute 1 for Z, infiinity for n final, so that becomes zero, then n = 2 into n initial. my answer ended up being 5.45e-19J, which is way too small for the answer...the answer provided was 328kJ. can any1 point out what im doing wrong? thanx

plz help me with this logartihm question: --- given that..... log xy = 2 log x + 2 determine the value of y for the following without using a calculator x = 3, 5, 10, 12 --- btw, i think the left side of the equation is actually: logx multiplied by y and not: log (xy) plz help!!

hey can any1 help me with dipole moments because im having trouble with deciding whether a molecule has a dipole moment or not.?

so that means Ag(NH3)2 2+ would be a lewis acid coz its positively charged...is that right?

any1 got any ideas for these 2 questions? 1. Identify the Lewis acid in the following reaction. Ag+(aq) + 2NH3(aq) --> Ag(NH3)2 2+(aq) 2. What is the concentration of hydroxide ions in a 0.035M solution of Ba(OH)2? (For Q1, I think Ag+ would be a lewis acid but what about the Ag(NH3)2 2+?) (For Q2, I think it's just 0.035 x 2 but...I'm not sure if that's right coz its sort of a guess...) thanx

can any1 give me some help on this question: What pressure would have to be applied to steam at 300 degrees C to condense it into liquid water (delta H(vap) = 40.7 kJ/mol)? Ans. 97.6 atm I really have no idea wat to do, i can't even start it!! i don't even know which formulae would be used...any1 got any ideas?

can any1 help me with this? "Which of the following will have the lowest total vapour pressure at 25 degrees C? a) pure water (vapour pressure = 23.8 torr at 25 degrees C) b) a solution of glucose in water with X(C6H12O6) = 0.01) c) a solution of sodium chloride in water with X(NaCl) = 0.01) d) a solution of methanol in water with X(CH3OH) = 0.2 (Consider the vapour pressure of both methanol [143 torr at 25 degrees C] and water)" I'm not sure whether it would be right if, say for b), I go P(total) = 0.99 x 23.8 = 23.562 (coz P of water would be 1 - 0.01 = 23.8)...i don't know becuase if that's right, then I will get the same answer for both b) and c)...but the answer at the back of the textbook says solution C will have the lowest total vapour pressure. so can any1 tell me what's going on?!?!

25ml 0.2 NaOH solution is added to 50ml of 0.1M acetic acid solution. What is the pH of the solution (Ka for acetic acid = 1.75e-5). i got an answer of pH = 9.378. does any1 agree? (my working out is so long that I thought if quite a few ppl agree with my ans. then i must be using the correct method...otherwise, if any of u guys reckon i've got the wrong ans, plz tell me so that i can figure out if my method is wrong) thanx

Can any1 help me with this? In a coffee-cup calorimeter, 50ml of 0.1M AgNO3 and 50ml of 0.1M HCl are mixed to yield the following reaction: Ag+(aq) + Cl-(aq) --> AgCl(s) The 2 solutions were initially at 22.6 degrees C and the final temperature is 23.4 degrees C. Calculate the heat that accompanies this reaction in kJ/mol of AgCl formed. Assume that the combined solution has a mass of 100g and a specific heat capacity of 4.18 J/degrees C g. I used q = ms(detaT) = 100 x 4.18 x 0.8 = 334.4J. I then thought since there are 0.01 mols altogether, then that means for 0.01 moles it's 334.4J, so 1 mole is 33440J. but that's the wrong answer. I think it's the moles part that's wrong - i'm not sure if it's ok to find moles of AgNO3, moles of HCl and then just add them up... then answer's -66kJ/mol

can any1 at all give me some help?

so doesn't any1 agree with my answers??