Calorimetry SAC

[HarveyD]

Hey guys

We performed an experiment whereby we calibrated a calorimeter (by heating up water)
Just wondering what kind of questions would be asked on the SAC cause theres not much in textbook...

Anyone know any errors as well?
I was thinking water being splashed out might be one...

[luken93]

Hahah I shall continue answering your questions

Basically, know how to determine the calibration factor, be able to apply this to measure different things, perhaps determine thermochemical equations.

As for errors, if it isn't properly insulated, too much/not enough stirring, not accurate volumes/measurements, faulty voltmeters etc.

[HarveyD]

hmm yeah, i guess it would have to be more general question for this SAC rather than talking about observations
I'll ask my teacher just to make sure though

thanks for that

[HarveyD]

with the insulation as an error, what effect would it have on the results?
Since change in T will be smaller, will it therefore decrease calibration factor and increase enthalpy value? (calculated values i mean)

also, if we were to sketch a graph on it, would the insulated calorimeter just remain constant after the temp rise, while non insulted one start decreasing (exponentially im guessing?)

and lastly, any other ways to minimise the source of error besides making sure the calorimeter is insulated?

[azn_dj]

The calibration factor will increase if there is poor insulation, as it will take more energy to heat the inside of the container. However, you will use the calibration factor to work out your answer, but you can't tell how much heat you lose because you can't control it! It does produce a random error because you cant measure what's lost. Graphically its the same, because you can't draw that precisely either.

Another possible source of error is if you don't stir it. The heat won't evenly distribute itself throughout the container.

[HarveyD]

hmm but when we did the prac, we kept the energy constant for all 3 trials (using same voltage)? so it wouldn't have any effect?
wouldnt an insulated calorimeter reach a higher temp than a non-insulated because energy will continuously be lost in the non insulted?
:S

[HarveyD]

can anyone confirm? :/

[luken93]

hmm but when we did the prac, we kept the energy constant for all 3 trials (using same voltage)? so it wouldn't have any effect?
wouldnt an insulated calorimeter reach a higher temp than a non-insulated because energy will continuously be lost in the non insulted?
:S

Remember that when calculating the Calibration Factor, it is Joules divided by change in temp. Hence;
Poorly insulated = Not much temp increase = Higher CB (lower denominator)
Well insulated = More temp increase - Lower CB (higher denominator)

[HarveyD]

ahh yeah, my bad
so would an insulated calorimeter increase the enthalpy change (since change in t is larger and t is the numerator for the delta H formula)?

Also would i be correct in saying that if I sketched a temp vs time graph for an insulated and poor insulted calorimeter, the well insulated one would remain constant after heating is finished, while the poorly insulated would increase then drop away after heating has stopped?

[HarveyD]

hmm so how would the enthalpy change if it wasnt well insulated?
Wouldn't the affected calibration factor be negated by the affected temperature change? (since they're both on the top in the formula for delta H)

[luken93]

Change in enthalpy differences will be the same as the calibration factor, as it is CB per mol. Since the mol calculation will be the same for both, it'll be the same..

Poorly insulated = Not much temp increase = Higher CB (lower denominator) = Higher Enthalpy
Well insulated = More temp increase - Lower CB (higher denominator) = Lower Enthalpy

Woops, my bad, forgot the enthalpy EQ 

I can't think off the top of my head, you'd probably have to do a couple of calculations to see if there is a predetermined effect, however, the change in temp is the denominator on the CB, but on the top for enthalpy, so if my maths is right the effect would cancel out?

[HarveyD]

ohh okay so when we are using the enthalpy change formula for the second reaction, the effect of the insulation on the temperature change can be considered negligible? ( delta H = CF x change in temp / number of mol )
Only the CF determined will affect our calculations

[luken93]

See edited post above.

[HarveyD]

dont think it wouldnt cancel out, cause the enthalpy change formula is used for the second reaction which would have a different change in temperature to the initial one which we used to calibrate it

its kinda confusing lol, hopefully my teacher only asks us about errors relating to the calibration factor

probably just say parallax errors when reading off the thermometer if she doesnt

[luken93]

dont think it wouldnt cancel out, cause the enthalpy change formula is used for the second reaction which would have a different change in temperature to the initial one which we used to calibrate it

its kinda confusing lol, hopefully my teacher only asks us about errors relating to the calibration factor

probably just say parallax errors when reading off the thermometer if she doesnt

Ha my bad again, I'm just gonna stop talking now, I need to go to sleep!