Suggested Answers - Illuminati

[thushan]

H(enthalpy)= U + pV
Hence saying pressure difference should be is correct

Oh yeah! thats also valid

[illuminati]

Wait so Illuminati, do you think the 2 mol/1mol ratio of combustion argument is ok? or not?

EDIT: This is for the deltaH question btw

I think it could work cos they were ambiguous

[Nobby]

H(enthalpy)= U + pV
Hence saying pressure difference should be is correct

Oh yeah! thats also valid

Pressure affects enthalpy? I thought that was just entropy?

[thushan]

*not in course

The definition of enthalpy is actually

H = U + PV

U is internal chemical energy, the "real" chemical energy.

Usually, change in H = change in U, as chemical reactions are generally done under atmospheric pressure.

Anyway, heat released = -change in enthalpy, when the reaction is done at constant pressure.
Heat released = -change in internal energy, when the reaction is done at constant VOLUME (as in a bomb calorimeter).

You are not taught this in VCE, you were taught to use enthalpy change to determine heat release in bomb calorimetry.

[Nobby]

For SA. 6)c)ii) would you pay an answer explaining how a catalyst increases reaction rate, then saying that this allows the cell to draw more current?

[doc2]

Time taken for the calcium carbonate to dissolve will probably be top answer. This is a standard prac technique and assessors are old dudes who remember that stuff.

There are heaps of answers. Temperature change, gas volume, take samples and measure Ca content, measure pH, Ca ion sensitive electrode, ...