[Twisted_Nucleics]

Hello!

This is my first time posting to the chemistry forums, so go easy on me!

I was doing an experiment on deducing the molar enthalpy of water, and the professor wants me to propagate the error for a single calculated value.

So ΔH(vap) = [(m.w.)(s)(m1)(dT/dt)(Δt)]/Δm
I find the molar enthalpy to be 40.09, and the theoretical value is 40.68 KJ/mole

If I go through and do a total differentiation on the above equation and apply the rules for propagation (i.e. squaring, negating cross terms, etc), I get:

σ_H = root[(Δm)(Δt)(dT/dt)σ_M1 + (m1)(Δt)(dT/dt)σ_Δm+(Δm)(m1)(dT/dt)σ_Δt + (Δm)(Δt)(m1)σ_dT/dt]

note: All terms under the root are squared, just trying to save myself some effort here.

But I don't know where to go from here and the whole idea is a bit confusing to me. I have seen it done on smaller functions, but nothing like this and not with real experimental variables, so I am lacking a solid example. Plus I always get hung up on error stuff. So many people just make up the error bars and take the small ding to their grade, but that gets you nowhere. I want to understand! I want to know!

I ask for help and I feel like I know what I am doing but I leave and woosh, it's lost again :/

Can anyone help me out?

Thanks.

[Vidya]

http://www.rit.edu/~w-uphysi/uncertainties/Uncertaintiespart2.html

Go through it .