Please tell me what I did wrong on these. (dS for formulas)?

Calculate DS in units of J/K for the formation of 1 mol of HI(g) from its elements in their standard states.

Work:

H(g) + I(g) > HI(g)

1mol HI 206.33J/K - ( 1mol H(g)114.60J/K + 1mol I(g)*180.67) =

-88.94 J/K

Calculate DS for the formation of 1 mole of PCl5(g) from the elements P4(s, white) and Cl2(g).

Work:

P4(s) + 10CL2(g) > 4PCl5

4353J/K - (41.1 J/K + 10223 J/K) = -859 J/K

Sulfur dioxide is released in the combustion of coal. Scrubbers remove much of the SO2 from the flue gases by reaction with lime slurries containing solid calcium hydroxide to form solid calcium sulfite and liquid water. Calculate So in units of J/K for the reaction of exactly one mole of sulfur dioxide gas in this scrubbing process at 298 K.

[So of calcium sulfite(s) = 101.4 J/mol.K]

My Work:

SO2 + calcium sulfite > CaSO4+H2O

(107+69.94) - (248.1+101.4) = -173 J/K

being that its at 298K I dont think i need to use G=H-TS

I think my problems lay with possibly the formula's I used to look up dS values. They look alright.

Oh yea, and I don't want people to think i'm asking someone to do my homework for me, this is just 3 out of 28 that I already finished and got corrected.

If someone could just look over my work and tell me where I went wrong, that would be awesome.

Thanks 🙂

Oh wow...duh, yea that was one big brain ƒᴀʀт. Started looking back over my equations after you guys pointed some stuff out, everything is all fixed now 🙂

Thankfully you hinted at what I was doing wrong, otherwise I would have been going wtf tommorow. (TEST!!)

3 Answers

  • You might want to try to re-read the questions. You don't appear to be understanding what is written there. (I call it a brain ƒᴀʀт, but three out of 28 indicates a little lack of understanding)

    If you have re-read the problems, then I offer the below:

    You might want to go over your notes about what a mole is. It is an amount and a number. It is a fundamental conceptual building block for the study of chemistry.

    It looks like you expect to be able to plug and chug on these. Which you can, once you start thinking in terms of atoms and molecules. Plugging and chugging BEFORE you understand what these little pieces are doing is a recipe for a C.

    It IS the ATOMIC theory of matter, don't you know.

    So, once you've absorbed that, re-read these three problems.

    Still no joy? Read on, Gunga DIn

    First H(g) is NOT the element's standard state! I thought everybody learned in grade school about H2 gas - the simplest molecule? Iodine, I leave to you (hint a gas???!!! not)

    Second lets see you're making umpteen moles of something and calculate the dS. that was not the question. (hint: something about ONE mole)

    Third read the problem. your chemical equation is from I don't know where but not from what is in the problem. (hint: products on the LEFT???)

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  • 1. It's H2 + I2 ----> 2HI.

    1. SO2 + Ca(OH)2 ---> CaSO3 + H2O

    Now you can get them right!

    Source(s): MA(Oxon)

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