ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: werdna on July 17, 2008, 05:31:50 pm

Title: Is change in enthalpy (delta H) counted for sig figs?
Post by: werdna on July 17, 2008, 05:31:50 pm

You know for RAMs, avogadro's no., gas constant 8.31, and other physical constants, you dont consider them for determining least sig figs. You only use experimental data yeah?
I'm not sure about the change in enthalpy they give in thermochemical Eqns
Any help would be good thanks

Title: Re: Is change in enthalpy (delta H) counted for sig figs?
Post by: Collin Li on July 17, 2008, 06:41:35 pm

All those constants are determined by experiments, so you should consider them. It's just that since those constants are so important, they're experimentally determined to a high accuracy, and hence the significant figures shouldn't be limiting - and don't matter (in practice you wouldn't use a value of R with 3 significant figures).

You should use the significant figures as given for R (3), RAMs (2-4, since VCAA only give to 1 decimal place) and other physical constants. This also includes reaction enthalpies.

Title: Re: Is change in enthalpy (delta H) counted for sig figs?
Post by: Pandemonium on August 05, 2008, 07:36:49 pm

If it doesn't involve the delta H, then it doesn't matter because it's not incorporated into the equation.

eg. If you're determining new concentration fractions at equilibrium, you wouldn't use delta H for the calculation, thus it is not included for significant figures.

However, if you're doing one of the calorimetry questions, then that would include delta H.