a Canadian

I did a lab today in class and part of the lab is to experimentally find the enthalpy for the dissolution of ammonium chloride by dissolving 4.0 g of NH4Cl(s) in 50.0 mL of H2O(l). I got a -5°C temperature change and calculated delta H to be 15 kJ/mol. Ac...

12 years ago

"Describe the characteristics of each graph (for example, . . . ., zero or non-zero intercept value)." I guess a zero intercept value would be if the line is on the point (0,0)/the origin. But what if the line starts at (0,1) or (2,0). Because then the x...

12 years ago

Had a recent mix-up when I re-read my chemistry notes, and trying to clear things up properly; is this right?: When bonds form, energy is released, and so the reaction absorbs energy. I have two different things written... a bond breaking results in energ...

12 years ago

Is this right?: Energy is absorbed in order to break bonds because bond breaking requires energy. Or are these two statements completely separate?: "energy is absorbed when bonds break" and "breaking bonds require energy"

12 years ago

I'm trying to write a sentence like this: Exothermic reactions have a negative enthalpy change value because the enthalpy of the reactants are greater than the enthalpy of the products since the reactants have weaker bonds.... Why do weaker bonds have hig...

12 years ago

Why is the enthalpy of the reactants greater than the enthalpy of the products in an exothermic reaction? If it has something to do with the reactants having weaker bonds, why do weaker bonds have higher energy/enthalpy? It doesn't really make sense to me...

12 years ago

Why wouldn't you do this reaction directly in a lab (and would rather use Hess' Law to determine the enthalpy of formation)?: 1/2N2(g) + 2H2(g)+ 1/2Cl2(g) -> NH4Cl(s) I don't think the reactants are that dangerous...? It's still pretty safe to do in a lab...

12 years ago

I wrote an introduction for a lab report for the first time, and I was given no samples (my teacher said "feel free to ask your friends who had chemistry last semester if you can see their introductions... none of my friends took it last semester, so I ha...

12 years ago

Firstly, is this right?: Exothermic reactions have a negative enthalpy change value because the enthalpy of the reactants are greater than the enthalpy of the products *since the reactants have weaker bonds.* (especially the starred part, I'm wondering ab...

12 years ago

Hi, here's my (almost) 2-paged lab report introduction (hopefully you remember it from yesterday). I went to class today, and actually a lot of my other classmates' introductions were over 2 pages! Now I'm feeling kind of insecure about mine, and I'm not...

12 years ago

Can you check my calculations, please? It's for a lab we did in order to find the the enthalpy of formation of NH4Cl(s). My final answer was -299.4 kJ, while the theoretical, or actual, value is -314.4 kJ. It was the closest value out of everyone in the e...

12 years ago

You know how when you do calculations for the enhaloy change of a reaction you start sort of like this?: NH3(aq) + HCl(aq) → NH4Cl(aq) 25 mL 25 mL 1.0 mol/L 1.0 mol/L n = c x v = 1 mol/L x 0.025L = 0.025 mol How come you only need the moles of one of the...

12 years ago

I had a quiz today and one of the multiple choice questions was something like, "find the final temperature of aluminum when it is cooled" and then it gave you the specific heat capacity of aluminum, the mass of the aluminum, initial temperature, and enth...

12 years ago

This is a chemistry lab report, but I was wondering if someone could edit the grammar and look at the sentence structure, etc. I know it's really long and boring, but even if you just look over a bit of it, I would really appreciate it. And I'm assuming y...

12 years ago

Mg + 2HCl -> MgCl2 + H2 Over an interval of 1.00s, the mass of Mg changes by -0.011g What is the corresponding rate of consumption of HCl (in mol/s)? I got 9.0E-4 mol/s and that's the right answer. But I'm having problems with the next question. Calculate...

12 years ago

A horse runs 15 m [N 23° E] and then 32 m [S 35° E]. What is the total displacement of the horse? I can't even visualise this... My friend told me the basic steps on how to solve it, but I got the wrong answer anyways... d1 = 15 m [N 23° E] d1x = 15m sin...

12 years ago

There's something wrong with this sentence but I can't put my finger on it!! The federal government has put into effect a mandate that requires all gasoline in Canada to contain 5 percent ethanol.

12 years ago

50 mL of copper(II) sulfate reacts with 50 mL of sodium hydroxide. Their concentrations are 0.3 M and 0.6 M respectively. The temperature increased to 23.6 C from 23.4 C. Determine the enthalpy change for the reaction in kJ/mol of sodium hydroxide. Q=mcΔT...

12 years ago

Factors affecting reaction rate. Use collision theory to explain. Factor: nature of the reactant Affect on rate: more or less reactive based on its chemical identity. reactivity: aq>g>l>s Explanation: For the other factors, we had to explain it based on w...

12 years ago

In the equation Q = mc(deltaT), I learned that Q means heat transfer. Is it the heat transfer from the system to the surroundings, i.e. the system loses/absorbs heat or is it from the surroundings to the system? A couple of places on the Internet say that...

12 years ago

Sodium methanoate, NaHCOO, and methanoic acid, HCOOH, can be used to make a buffer solution. Explain how this combination resists changes in pH when small amounts of acid or base are added. Buffers kind of confuse me and I'm not sure how to start this. Ca...

12 years ago

Ca(OH)2, CaF2, NH4NO3, KNO3, HNO3 - Arrange the solutions from most basic to most acidic. I know Ca(OH)2 will be most basic and HNO3 will be most acidic, but how do you determine for the other ones?

12 years ago

The Ksp for nickel(II) hydroxide is 5.47E-16. What is the base dissociation constant for nickel(II) hydroxide? So I started off doing Ni(OH)2 (s) <-> Ni2+ (aq) + 2OH- (aq) I ..........................0 .................0 C ........................+x ........

12 years ago

I'm reviewing for a test and I'm on Le Chatelier's principle. Decreasing the temperature of an exothermic reaction shifts the equilibrium to the right? I understood this weeks ago but now I can't remember. Wouldn't decreasing the temperature cause there t...

12 years ago

Okay, I feel like this question should be really easy because it's a multiple choice question but how do you figure it out?? I'm completely drawing a blank. Consider the following equilibrium N2O4(g) <-> 2NO2(g) Kc = 4.8E-3 Which set of concentrations rep...

12 years ago

20.00mL of a 1.100E-4 mol/L Pb(NO3)2 is mixed with 80.00mL of 4.450E-2 mol/L CaI2. Will a precipitate form? Here's what I did... [Pb2+] c=n/v = (1.1E-4 mol/L x 0.02L)/(0.02L + 0.08L) = 2.2E-5 mol/L [I-] c=n/v = (4.45E-2 mol/L x 0.08L)/0.1L = 3.56E-2 mol/L...

12 years ago

Explain why iron corrodes more quickly in seawater than in freshwater. I'm getting conflicting answers from searching on Google; is it because the corrosion of iron is a redox reaction, which involves a transfer of electrons, and therefore this transfer o...

12 years ago

Name each compound. /\/\NH2 (that's suppose to be a line diagram...) I got 1-pentanamine, but that's wrong. CH3CH2-O-CHCH2CH3 .....................| ..................CH3 I'm not sure how great this will turn out, but there's supposed to be a CH3 branchin...

12 years ago

How do you draw N,N-dimethylheptanamine? The N,N part is confusing me most.

12 years ago

I'm having a lot of trouble with Naming organic compounds when given things like HCOOCH2CH2CH3. Can you recommend some steps? How do you identify the branches?? And would the example I have above be a carboxylic acid? My teacher said that it might help to...

12 years ago

................CH3 ..................| CH3-CH2-N-CH2-CH2-CH3 Hoping this turns out okay, but it's an amine and branching off of the N (on top) is a CH3. The name is N-ethyl-N-methylpropanamine but I don't get why. How do you know which ones to treat as b...

12 years ago

I understood this at one point and now I'm confused again! :( What's the difference between 2,2-dimethyl and 2-ethyl? It's hard to find proper drawings online... For example, for naming CH3CH2C(CH3)2CH2NH2, Why wouldn't it be 2-ethyl-1-butanamine rather t...

12 years ago

Apoarently the name of this compound is 4-ethyl-4-methylheptane: ........................CH3 ..........................| CH3-CH2-CH2-C-CH2-CH3 ..........................| .......................CH2 ..........................| .......................CH2 .....

12 years ago

How would you be able to recognise that C5H8 was an alkyne? And how would you know that CH3COCH3 was a ketone? (I thought it was an ether)

12 years ago

Reviewing for exams and completely forgot how to do this and looking back at my notes doesn't help for this one... Can you please explain how to assign oxidation numbers for Pb(OH)4^2- I guess what's confusing me is the hydroxide... I haven't come across...

12 years ago

(delta)Eg = -14.7J Therefore, Ek = -(delta)Eg = 14.7J I don't understand how you'd come to the above conclusion? Does Ek just always equal -(delta)Eg?

12 years ago

So for the neutralisation one I'm way off, right? Is it unacceptably off? Because my teacher said we'd have tomorrow to continue if we didn't finish, so I might just do that part again. That makes more sense, thanks so much for answering (for all the othe...

12 years ago

i.e. is energy absorption a result of breaking bonds, or is energy absorbed in order to break bonds? So like... Energy is required to break bonds. Energy is somehow obtained, the bonds break... and this results in the absorption of *different* energy (whi...

12 years ago

This question came up because I'm trying to write for the introduction in my lab report, "Energy is required to break bonds, so when bonds break, energy is absorbed". But that sounded off (because that's like saying the absorption of energy when bonds bre...

12 years ago

Sorry, I think this sentence should be alright, "Energy is required to break bonds, and when the bonds break, energy is absorbed." Don't know why I had to go through all that trouble to reach this simple sentence, but...

12 years ago

Basically, ignore the rest of my question if the above sentence is okay.

12 years ago

It's just that I have to include both ideas together in a paragraph and I writing, "Energy is required to break a bond. Breaking a bond requires energy." doesn't have "flow" and would work better in one sentence.

12 years ago

I'm basically trying to explain why, in exothermic reactions, enthalpy of the products are greater than the enthalpy of the reactants (resulting in a negative enthalpy change). And I obviously don't know myself. Can someone please explain? I can't seem to...

12 years ago

But that would happen AFTER a reaction... Why would a reaction end up being expthermic if, originally, the enthalpy of the reactants are greater than the enthalpy of the products. And also, why do weaker bonds have more enthalpy/energy?

12 years ago

I thought it might be kind of obnoxious of me to just post two pages worth of stuff and ask someone to read it, but thank you so much for being willing to look at it, I'll definitely repost tomorrow! Thanks for answering, and good night!

12 years ago

Oh no! :( I tried to sum up the stuff as best as I could and be brief since I felt that two pages was way too long, but now I feel like I shouldn't have done that... I'll ask her tomorrow how much detail she expects, etc. because I don't really think mine...

12 years ago

Oh, oops ! I forgot to put x100 and then the rest of my answer, 4.8% (or 5%) I think it's a small miracle that I didn't make any mistakes when calculating the enthalpy of formation, there were a ton of steps! Thank you so much!

12 years ago

So if you find the enthalpy change for one reactant, it's the enthalpy change for the other reactant (and products??), i.e. you know the enthalpy change for the entire reaction? So enthalpy change of one reactant (or product also?) = enthalpy change of en...

12 years ago

That's what I don't really understand. If it's of the total reaction, shouldn't you add, in my example, the moles of both reactants? i.e. 0.025 +0.025 = 0.05 mol. Then use that value when doing deltaH = -Q/n? How come you only use The moles of one?

12 years ago

Thanks; I obviously got it wrong, but what was my teacher talking about when she said that when you have a solid reacting, you don't use the mass of the solid for Q=mc(deltaT), only the mass of liquids or solutions? Why wouldn't that apply in this case?

12 years ago

Hi Writeacher, I was wondering if you could take a look at my question jiskha(dot)com/display.cgi?id=1361488610 I don't know if you already have and decided not to answer it (never mind if you already did look at it), it's just that I've seen you edit som...

12 years ago

That's alright, thanks though.

12 years ago

I actually already got one to read it and he said, "I see nothing 'wrong'." so I guess nothing "wrong" with quotes would mean there are some technical issues or something, I don't know. but this time around I was loOking more for a grammar check, but I ca...

12 years ago

I don't mean to sound rude, but you couldn't have read that all in less than a minute and so you couldn't have truly come to that conclusion. Please don't give false feedback.

12 years ago

(which is why I put it under English this time, rather than chemistry)

12 years ago

If it is feedback on only a small portion of it which could be read quickly, then thank you, but it did not come off that way.

12 years ago

Maybe another "that" after "requires"?? The "...that ____ that..." bothers me though. Too many 'that's!

12 years ago

and if another "that" was added then "to" would change to "must", I guess?

12 years ago

The example problem I gave is the root of all my confusion... Before, I always though when you do Q=mc(deltaT), you're getting the amount of heat absorbed/released by the SURROUNDINGS, and so when you want to get deltaH, you'd have to make Q negative in o...

12 years ago

Oh okay so they have two distinct jobs, but they're still together in the solution? For example in a lab or something, both chemicals would be mixed inside one beaker? Is this explanation right?: If an acid is added, the H3O+ ions will be removed by NaHCO...

12 years ago

Oh, are the other three salts? And you just have to see whether they're acidic or basic or neutral salts? I got that KNO3 was neutral, CaF2 was basic and NH4NO3 was acidic? So.. Ca(OH)2, CaF2, KNO3, NH4NO3, HNO3? Is there another way I should be doing thi...

12 years ago

I forgot to write ^2 on the [I-] for Qsp. Just a typo though, I did square it when I punched it in my calculator.

12 years ago

..........CH3...................................CH3 ............|..........................................| CH3 -- C -- C =(triple bond)= C -- C -- CH3 ............|..........................................| ...........CH3..................................

12 years ago

And how would you know something was a cyclic hydrocarbon when given something like CH3CH2COOH? (I know that one isn't a cyclic hydrocarbon but I mean like when you get questions saying "name the organic compound" and they give stuff like CH3CH2COOH and C...

12 years ago

No, sorry, it'd be an ester right?

12 years ago

And how would you know if there's double bonds?

12 years ago

Also, if there's branches coming off of it, what do you do? For example, if the left part had a branch: CH3 ...| CH3-CH2-N Or would that just be extending the branch? And it would make the "N-ethyl" into "N-propyl"?

12 years ago

Sorry, I keep thinking of more stuff... Complications always magically arise right before an evaluation and never while I can actually ask my teacher :( Can there be more than three in a branch? So far we've only done ones with methyl, ethyl, and propyl,...

12 years ago